Audio Signal Decoder, Audio Signal Encoder, Method for providing an Upmix Signal
Representation, Method for Providing a Downmix Signal Representation, Computer
Program and Bitstream using a Common Inter-Object-Correlation Parameter Value
Description
Technical Field
Embodiments according to the invention are related to an audio signal decoder for
providing an upmix signal representation on the basis of a downmix signal representation
and an object-related parametric information and in dependence on a rendering
information.
Other embodiments according to the invention relate to an audio signal encoder for
providing a bitstream representation on the basis of a plurality of audio object signals.
Other embodiments according to the invention relate to a method for providing an upmix
signal representation on the basis of a downmix signal representation and an object-related
parametric information and in dependence on a rendering information.
Other embodiments according to the invention relate to a method for providing a bitstream
representation on the basis of a plurality of audio object signals.
Other embodiments according to the invention are related to a computer program for
performing said methods.
Other embodiments according to the invention are related to a bitstream representing a
multi-channel audio signal.
Background of the Invention
In the art of audio processing, audio transmission and audio storage, there is an increasing
desire to handle multi-channel contents in order to improve the hearing impression. Usage
of multi-channel audio content brings along significant improvements for the user. For
example, a 3-dimensional hearing impression can be obtained, which brings along an
improved user satisfaction in entertainment applications. However, multi-channel audio

contents are also useful in professional environments, for example in telephone
conferencing applications, because the speaker intelligibility can be improved by using a
multi-channel audio playback.
However, it is also desirable to have a good tradeoff between audio quality and bitrate
requirements in order to avoid an excessive resource load caused by multi-channel
applications.
Recently, parametric techniques for the bitrate-efficient transmission and/or storage of
audio scenes containing multiple audio objects have been proposed, for example, Binaural
Cue Coding (Type I) (see, for example reference [BCC]), Joint Source Coding (see, for
example, reference [JSC]), and MPEG Spatial Audio Object Coding (SAOC) (see, for
example, references [SAOC1], [SAOC2] and non-prepublished reference [SAOC]).
These techniques aim at perceptually reconstructing the desired output audio scene rather
than a waveform match.
Fig. 8 shows a system overview of such a system (here: MPEG SAOC). In addition, Fig.
9a shows a system overview of such a system (here: MPEG SAOC).
The MPEG SAOC system 800 shown in Fig. 8 comprises an SAOC encoder 810 and an
SAOC decoder 820. The SAOC encoder 810 receives a plurality of object signals x1 to XN,
which may be represented, for example, as time-domain signals or as time-frequency-
domain signals (for example, in the form of a set of transform coefficients of a Fourier-
type transform, or in the form of QMF subband signals). The SAOC encoder 810 typically
also receives downmix coefficients d1 to dN, which are associated with the object signals x1
to xN. Separate sets of downmix coefficients may be available for each channel of the
downmix signal. The SAOC encoder 810 is typically configured to obtain a channel of the
downmix signal by combining the object signals x1 to xN in accordance with the associated
downmix coefficients d1 to dN. Typically, there are less downmix channels than object
signals x1 to xN. In order to allow (at least approximately) for a separation (or separate
treatment) of the object signals at the side of the SAOC decoder 820, the SAOC encoder
810 provides both the one or more downmix signals (designated as downmix channels)
812 and a side information 814. The side information 814 describes characteristics of the
object signals x1 to XN, in order to allow for a decoder-sided object-specific processing.
The SAOC decoder 820 is configured to receive both the one or more downmix signals
812 and the side information 814. Also, the SAOC decoder 820 is typically configured to

receive a user interaction information and/or a user control information 822, which
describes a desired rendering setup. For example, the user interaction information/user
control information 822 may describe a speaker setup and the desired spatial placement of
the objects, which provide the object signals x1 to XN.
The SAOC decoder 820 is configured to provide, for example, a plurality of decoded
upmix channel signals ŷ1 to ŷM. The upmix channel signals may for example be associated
with individual speakers of a multi-speaker rendering arrangement. The SAOC decoder
820 may, for example, comprise an object separator 820a, which is configured to
reconstruct, at least approximately, the object signals x1 to XN on the basis of the one or
more downmix signals 812 and the side information 814, thereby obtaining reconstructed
object signals 820b. However, the reconstructed object signals 820b may deviate
somewhat from the original object signals x1 to xN, for example, because the side
information 814 is not quite sufficient for a perfect reconstruction due to the bitrate
constraints. The SAOC decoder 820 may further comprise a mixer 820c, which may be
configured to receive the reconstructed object signals 820b and the user interaction
information/user control information 822, and to provide, on the basis thereof, the upmix
channel signals ŷ1 to ŷM. The mixer 820 may be configured to use the user interaction
information /user control information 822 to determine the contribution of the individual
reconstructed object signals 820b to the upmix channel signals ŷ1 to ŷM. The user
interaction information/user control information 822 may, for example, comprise rendering
parameters (also designated as rendering coefficients), which determine the contribution of
the individual reconstructed object signals 822 to the upmix channel signals ŷ1 toŷM-
However, it should be noted that in many embodiments, the object separation, which is
indicated by the object separator 820a in Fig. 8, and the mixing, which is indicated by the
mixer 820c in Fig. 8, are performed in single step. For this purpose, overall parameters
may be computed which describe a direct mapping of the one or more downmix signals
812 onto the upmix channel signals ŷ1 to ŷM. These parameters may be computed on the
basis of the side information and the user interaction information/user control information
820.
Taking reference now to Figs. 9a, 9b and 9c, different apparatus for obtaining an upmix
signal representation on the basis of a downmix signal representation and object-related
side information will be described. Fig. 9a shows a block schematic diagram of a MPEG
SAOC system 900 comprising an SAOC decoder 920. The SAOC decoder 920 comprises,
as separate functional blocks, an object decoder 922 and a mixer/renderer 926. The object
decoder 922 provides a plurality of reconstructed object signals 924 in dependence on the

downmix signal representation (for example, in the form of one or more downmix signals
represented in the time domain or in the time-frequency-domain) and object-related side
information (for example, in the form of object meta data). The mixer/renderer 924
receives the reconstructed object signals 924 associated with a plurality of N objects and
provides, on the basis thereof, one or more upmix channel signals 928. In the SAOC
decoder 920, the extraction of the object signals 924 is performed separately from the
mixing/rendering, which allows for a separation of the object decoding functionality from
the mixing/rendering functionality but brings along a relatively high computational
complexity.
Taking reference now to Fig. 9b, another MPEG SAOC system 930 will be briefly
discussed, which comprises an SAOC decoder 950. The SAOC decoder 950 provides a
plurality of upmix channel signals 958 in dependence on a downmix signal representation
(for example, in the form of one or more downmix signals) and an object-related side
information (for example, in the form of object meta data). The SAOC decoder 950
comprises a combined object decoder and mixer/renderer, which is configured to obtain
the upmix channel signals 958 in a joint mixing process without a separation of the object
decoding and the mixing/rendering, wherein the parameters for said joint upmix process
are dependent both on the object-related side information and the rendering information.
The joint upmix process depends also on the downmix information, which is considered to
be part of the object-related side information.
To summarize the above, the provision of the upmix channel signals 928, 958 can be
performed in a one-step process or a two-step process.
Taking reference now to Fig. 9c, an MPEG SAOC system 960 will be described. The
SAOC system 960 comprises an SAOC to MPEG Surround transcoder 980, rather than an
SAOC decoder.
The SAOC to MPEG Surround transcoder comprises a side information transcoder 982,
which is configured to receive the object-related side information (for example, in the form
of object meta data) and, optionally, information on the one or more downmix signals and
the rendering information. The side information transcoder is also configured to provide an
MPEG Surround side information (for example, in the form of an MPEG Surround
bitstream) on the basis of a received data. Accordingly, the side information transcoder 982
is configured to transform an object-related (parametric) side information, which is
relieved from the object encoder, into a channel-related (parametric) side information,

taking into consideration the rendering information and, optionally, the information about
the content of the one or more downmix signals.
Optionally, the SAOC to MPEG Surround transcoder 980 may be configured to manipulate
the one or more downmix signals, described, for example, by the downmix signal
representation, to obtain a manipulated downmix signal representation 988. However, the
downmix signal manipulator 986 may be omitted, such that the output downmix signal
representation 988 of the SAOC to MPEG Surround transcoder 980 is identical to the input
downmix signal representation of the SAOC to MPEG Surround transcoder. The downmix
signal manipulator 986 may, for example, be used if the channel-related MPEG Surround
side information 984 would not allow to provide a desired hearing impression on the basis
of the input downmix signal representation of the SAOC to MPEG Surround transcoder
980, which may be the case in some rendering constellations.
Accordingly, the SAOC to MPEG Surround transcoder 980 provides the downmix signal
representation 988 and the MPEG Surround bitstream 984 such that a plurality of upmix
channel signals, which represent the audio objects in accordance with the rendering
information input to the SAOC to MPEG Surround transcoder 980 can be generated using
an MPEG Surround decoder which receives the MPEG Surround bitstream 984 and the
downmix signal representation 988.
To summarize the above, different concepts for decoding SAOC-encoded audio signals can
be used. In some cases, a SAOC decoder is used, which provides upmix channel signals
(for example, upmix channel signals 928, 958) in dependence on the downmix signal
representation and the object-related parametric side information. Examples for this
concept can be seen in Figs. 9a and 9b. Alternatively, the SAOC-encoded audio
information may be transcoded to obtain a downmix signal representation (for example, a
downmix signal representation 988) and a channel-related side information (for example,
the channel-related MPEG Surround bitstream 984), which can be used by an MPEG
Surround decoder to provide the desired upmix channel signals.
In the MPEG SAOC system 800, a system overview of which is given in Fig. 8, and also in
the MPEG SAOC system 900, a system overview of which is given in Fig. 9, the general
processing is carried out in a frequency selective way and can be described as follows
within each frequency band:
• N input audio object signals x1 to XN are downmixed as part of the SAOC encoder
processing. For a mono downmix, the downmix coefficients are denoted by d1 to dN. In

addition, the SAOC encoder 810, 910 extracts side information 814 describing the
characteristics of the input audio objects. An important part of this side information
consists of relations of the object powers and correlations with respect to each other,
i.e., object-level differences (OLDs) in inter-object-correlations (IOCs).
• Downmix signal (or signals) 812, 912 and side information 814, 914 are transmitted
and/or stored. To this end, the downmix audio signal may be compressed using well-
known perceptual audio coders such as MPEG-1 Layer II or III (also known as
".mp3"), MPEG Advanced Audio Coding (AAC), or any other audio coder.
• On the receiving end, the SAOC decoder 820, 920 conceptually tries to restore the
original object signals ("object separation") using the transmitted side information 814,
914 (and, naturally, the one or more downmix signals 812, 912). These approximated
object signals (also designated as reconstructed object signals 820b, 924) are then
mixed into a target scene represented by M audio output channels (which may, for
example, be represented by the upmix channel signals ŷi to ŷM, 928) using a rendering
matrix. For a mono output, the rendering matrix coefficients are given by r1 to rN
• Effectively, the separation of the object signals is rarely executed (or even never
executed), since both the separation step (indicated by the object separator 820a, 922)
and the mixing step (indicated by the mixer 820c, 926) are combined into a single
transcoding step, which often results in an enormous reduction in computational
complexity.
It has been found that such a scheme is tremendously efficient, both in terms of
transmission bitrate (it is only necessary to transmit a few downmix channels plus some
side information instead of N object audio signals) and computational complexity (the
processing complexity relates mainly to the number of output channels rather than the
number of audio objects). Further advantages for the user on the receiving end include the
freedom of choosing a rendering setup of his/her choice (mono, stereo, surround,
virtualized headphone playback, and so on) and the feature of user interactivity: the
rendering matrix, and thus the output scene, can be set and changed interactively by the
user according to will, personal preference or other criteria. For example, it is possible to
locate the talkers from one group together in one spatial area to maximize discrimination
from other remaining talkers. This interactivity is achieved by providing a decoder user
interface:

For each transmitted sound object, its relative level and (for non-mono rendering) spatial
position of rendering can be adjusted. This may happen in real-time as the user changes the
position of the associated graphical user interface (GUI) sliders (for example: object-level
= +5dB, object position = -30deg).
In the following, a short reference will be given to techniques, which have been applied
previously in the field of channel-based audio coding.
US 11/032,689 describes a process for combining several cue values into a single
transmitted one in order to save side information.
This technique is also applied to "multi-channel hierarchal audio coding with compact side
information" in US 60/671,544.
However, it has been found that the object-related parametric information, which is used
for an encoding of a multi-channel audio content, comprises a comparatively high bit rate
in some cases.
Accordingly, it is an objective of the present invention to create a concept, which allows
for a provision, storage or transmission of a multi-channel audio content with a compact
side information.
Summary of the Invention
This objective is achieved by an audio signal decoder, an audio signal encoder, a method
for providing an upmix signal representation, a method for providing a bitstream
representation, a computer program and a bitstream as defined by the independent claims.
An embodiment according to the invention creates an audio signal decoder for providing
an upmix signal representation on the basis of a downmix signal representation and an
object-related parametric information and in dependence on a rendering information. The
apparatus comprises an object-parameter determinator configured to obtain inter-object-
correlation values for a plurality of pairs of audio objects. The object-parameter
determinator is configured to evaluate a bitstream signalling parameter in order to decide
whether to evaluate individual inter-object-correlation bitstream parameter values to obtain
inter-object-correlation values for a plurality of pairs of related audio objects or to obtain
inter-object-correlation values for a plurality of pairs of related audio objects using a
common inter-object-correlation bitstream parameter value. The audio signal decoder also

comprises a signal processor configured to obtain the upmix signal representation on the
basis of the downmix signal representation and using the inter-object-correlation values for
a plurality of pairs of related audio objects and the rendering information.
This audio signal decoder is based on the key idea that a bit rate required for encoding
inter-object-correlation values can be excessively high in some cases in which correlations
between many pairs of audio objects need to be considered in order to obtain a good
hearing impression, and that a bit rate required to encode the inter-object-correlation values
can be significant reduced in such cases by using a common inter-object-correlation
bitstream parameter value rather than individual inter-object-correlation bitstream
parameter values without significantly compromising the hearing impression.
It has been found that in situations in which there are notable inter-object-correlations
between many pairs of audio objects, which should be considered in order to obtain a good
hearing impression, a consideration of the inter-object-correlations would normally result
in a high bitrate requirement for the inter-object-correlation bitstream parameter values.
However, it has been found that in such situations, in which there is a non-negligible inter-
object-correlation between many pairs of audio objects, a good hearing impression can be
achieved by merely encoding a single common inter-object-correlation bitstream parameter
value, and by deriving the inter-object-correlation values for a plurality of pairs of related
audio objects from such a common inter-object-correlation bitstream parameter value.
Accordingly, the correlation between many audio objects can be considered with sufficient
accuracy in most cases, while keeping the effort for the transmission of the inter-object-
correlation bitstream parameter value sufficiently small.
Therefore, the above-discussed concept results in a small bit rate demand for the object-
related side information in some acoustic environments in which there is a non-negligible
inter-object-correlation between many different audio object signals, while still achieving a
sufficiently good hearing impression.
In a preferred embodiment, the object-parameter determinator is configured to set the inter-
object-correlation value for all pairs of different related audio objects to a common value
defined by the common inter-object-correlation bitstream parameter value. It has been
found that this simple solution brings along a sufficiently good hearing impression in many
relevant situations.
In a preferred embodiment, the object-parameter determinator is configured to evaluate an
object-relationship information describing whether two objects are related to each other or

not. The object-parameter determinator is further configured to selectively obtain inter-
object-correlation values for pairs of audio objects for which the object-relationship
information indicates a relationship using the common inter-object-correlation bitstream
parameter value, and to set inter-object-correlation values for pairs of audio objects for
which the object-relationship information indicates no relationship to a predefined value
(for example, to zero). Accordingly, it can be distinguished, with high bitrate efficiency,
between related and unrelated audio objects. Therefore, an allocation of a non-zero inter-
object-correlation value to pairs of audio objects, which are (approximately) unrelated, is
avoided. Accordingly, a degradation of a hearing impression is avoided and a separation
between such approximately unrelated audio objects is possible. Moreover, the signalling
of related and unrelated audio objects can be performed with very high bitrate efficiency,
because the audio object relationship is typically time-invariant over a piece of audio, such
that the required bitrate for this signalling is typically very low. Thus, the described
concept brings along a very good trade-off between bitrate efficiency and hearing
impression.
In a preferred embodiment, the object parameter determinator is configured to evaluate an
object-relationship information comprising a one-bit flag for each combination of different
audio objects, wherein the one-bit flag associated to a given combination of different audio
objects indicates whether the audio objects of the given combination are related or not.
Such an information can be transmitted very efficiently and results in a significant
reduction of the required bit rate to achieve a good hearing impression.
In a preferred embodiment, the object-parameter determinator is configured to set the inter-
object-correlation values for all pairs of different related audio objects to a common value
defined by the common inter-object-correlation bitstream parameter value.
In a preferred embodiment, the object-parameter determinator comprises a bitstream parser
configured to parse a bitstream representation of an audio content to obtain the bitstream
signalling parameter and the individual inter-object-correlation bitstream parameters or the
common inter-object-correlation bitstream parameter. By using a bitstream parser, the
bitstream signalling parameter and the individual inter-object-correlation bitstream
parameters or the common inter-object-correlation bitstream parameter can be obtained
with good implementation efficiency.
In a preferred embodiment, the audio signal decoder is configured to combine an inter-
object-correlation value associated with a pair of related audio objects with an object-level
difference parameter value describing an object level of a first audio object of the pair of

related audio objects and with an object-level difference parameter value describing an
object level of a second audio object of the pair of related audio objects to obtain a
covariance value associated with the pair of related audio objects. Accordingly, it is
possible to derive the covariance value associated to a pair of related audio objects such
that the covariance value is adapted to the pair of audio objects even though a common
inter-object-correlation parameter is used. Therefore, different covariance values can be
obtained for different pairs of audio objects. In particular, a large number of different
covariance values can be obtained using the common inter-object-correlation bitstream
parameter value.
In a preferred embodiment, the audio signal decoder is configured to handle three or more
audio objects. In this case, the object-parameter determinator is configured to provide
inter-object-correlation values for every pair of different audio objects. It has been found
that meaningful values can be obtained using the inventive concept even if there are a
relatively large number of audio objects, which are all related to each other. Obtaining
inter-object-correlation values from many combinations of audio objects is particularly
helpful when encoding and decoding audio object signals using an object-related
parametric side information.
In a preferred embodiment, the object-parameter determinator is configured to evaluate the
bitstream signalling parameter, which is included in a configuration bitstream portion, in
order to decide whether to evaluate individual inter-object-correlation bitstream parameter
values to obtain inter-object-correlation values for a plurality of pairs of related audio
objects or to obtain inter-object-correlation values for a plurality of pairs of related audio
objects using a common inter-object-correlation bitstream parameter value. In this
embodiment, the object-parameter determinator is configured to evaluate an object
relationship information, which is included in the configuration bitstream portion, to
determine whether the audio objects are related. In addition, the object-parameter
determinator is configured to evaluate a common inter-object-correlation bitstream
parameter value, which is included in a frame data bitstream portion, for every frame of the
audio content if it is decided to obtain inter-object-correlation values for a plurality of pairs
of related audio objects using a common inter-object-correlation bitstream parameter
value. Accordingly, a high bitrate efficiency is obtained, because the comparatively large
object relationship information is evaluated only once per audio piece (which is defined by
the presence of a configuration bitstream portion), while the comparatively small common
inter-object-correlation bitstream parameter value is evaluated for every frame of the audio
piece, i.e. multiple times per audio piece. This reflects the finding that the relationship
between audio objects typically does not change within an audio piece or only changes

very rarely. Accordingly, a good hearing impression can be obtained at a reasonably low
bitrate.
Alternatively, however, the usage of a common inter-object-correlation bitstream
parameter value could be signaled in a frame data bitstream portion, which would, for
example, allow for a flexible adaptation to varying audio contents.
An embodiment according to the invention creates an audio signal encoder for providing a
bitstream representation on the basis of a plurality of audio object signals. The audio signal
encoder comprises a downmixer configured to provide a dowmix signal on the basis of the
audio object signals and in dependence on downmix parameters describing contributions of
the audio object signals to be one or more channels of the downmix signal. The audio
signal encoder also comprises a parameter provider configured to provide a common inter-
object-correlation bitstream parameter value associated with a plurality of pairs of related
audio object signals and to also provide a bitstream signalling parameter indicating that the
common inter-object-correlation bitstream parameter value is provided instead of a
plurality of individual inter-object-correlation bitstream parameters. The audio signal
encoder also comprises a bitstream formatter configured to provide a bitstream comprising
a representation of the downmix signal, a representation of the common inter-object-
correlation bitstream parameter value and the bitstream signalling parameter.
This embodiment, according to the invention, allows for a provision of a bitstream
representing a multi-channel audio content with compact side information. By providing a
common inter-object-correlation bitstream parameter value, the object-related side
information is held compact, while still providing efficient information for a reproduction
of the multi-channel audio content with a good hearing impression. In addition, it should
be noted that the audio signal encoder described here provides for the same advantages
which have been discussed with respect to the audio signal decoder.
In a preferred embodiment, the parameter provider is configured to provide the common
inter-object-correlation bitstream parameter value in dependence on a ratio between a sum
of cross-power terms and a sum of average power terms. It has been found that such an
inter-object-correlation bitstream parameter value can be computed with moderate
computational effort, while still providing an accurate hearing impression in most cases.
In another embodiment according to the invention, the parameter provider is configured to
provide a predetermined constant value as the common inter-object-correlation bitstream
parameter value. It has been found that in some cases, the provision of a constant value

makes sense. For example, for certain standard microphone arrangements in certain types
of conference rooms, a constant value may be very well suited to represent a desired
hearing impression. Accordingly, the computational effort can be minimized while
providing a good hearing impression in many standard applications of the inventive
concept.
In another preferred embodiment, the parameter provider is configured to also provide an
object-relationship information describing whether two audio objects are related to each
other. Such an object-relationship information can be exploited by the audio decoder, as
discussed above. Accordingly, it can be ensured that the common inter-object-correlation
bitstream parameter value is only applied for such audio objects, which are, indeed, related
to each other, but is not applied to entirely unrelated audio objects.
In a preferred embodiment, the parameter provider is configured to selectively evaluate an
inter-object-correlation of audio objects for which the object-relationship information
indicates a relationship for a computation of the common inter-object-correlation bitstream
parameter value. This allows to have a particularly meaningful inter-object-correlation
bitstream parameter value.
Further embodiments according to the invention create a method for providing an upmix
signal representation and a method for providing a bitstream representation. These methods
are based on the same ideas as the above-discussed audio decoder and audio encoder.
Another embodiment according to the invention creates a bitstream representing a multi-
channel audio signal. The bitstream comprises a representation of a downmix signal
combining audio signals of a plurality of audio objects. The bitstream also comprises an
object-related parametric side information describing characteristics of the audio objects.
The object-related parametric side information comprises a bitstream signaling parameter
indicating whether the bitstream comprises individual inter-object-correlation bitstream
parameter values or a common inter-object-correlation bitstream parameter value.
Accordingly, the bitstream allows for a flexible usage for the transmission of different
types of audio-channel contents. In particular, the bitstream allows for both the
transmission of the individual inter-object-correlation bitstream parameter values or of the
common inter-object-correlation bitstream parameter value, whichever is more suited for
the auditory scene. Accordingly, the bitstream is well-suited for handling both cases in
which there is a comparatively small number of related audio objects for which detailed
(object-individual) inter-object-correlation information should be transmitted and for cases
in which there is a comparatively large number of related audio objects for which a

transmission of individual inter-object-correlation bitstream parameter values would result
in an excessively high bitrate demand and for which a common inter-object-correlation
bitstream parameter value still allows for a reproduction with a good hearing impression.
Brief Description of the Figs.
Embodiments according to the invention will subsequently be described taking reference to
the enclosed Figs, in which:
Fig. 1 shows a block schematic diagram of an audio signal decoder according to an
embodiment of the invention;
Fig. 2 shows a block schematic diagram of an audio signal encoder according to an
embodiment of the invention;
Fig. 3 shows a schematic representation of a bitstream according to an
embodiment of the invention;
Fig. 4 shows a block schematic diagram of an MPEG SAOC system using a single
inter-object-correlation parameter calculation;
Fig. 5 shows a syntax representation of an SAOC specific configuration
information, which may be part of a bitstream;
Fig. 6 shows a syntax representation of an SAOC frame information, which may
be part of a bitstream;
Fig. 7 shows a table representing a parameter quantization of the inter-object-
correlation parameter;
Fig. 8 shows a block schematic diagram of a reference MPEG SAOC system;
Fig. 9a shows a block schematic diagram of a reference SAOC system using a
separate decoder and mixer;
Fig. 9b shows a block schematic diagram of a reference SAOC system using an
integrated decoder and mixer; and

Fig. 9c shows a block schematic diagram of a reference SAOC system using an
SAOC-to-MPEG transcoder.
Detailed Description of the Embodiments
1. Audio Signal Decoder according to Fig. 1
In the following, an audio signal decoder 100 will be described taking reference to Fig. 1,
which shows a block schematic diagram of such an audio signal decoder 100.
Firstly, input and output signals of the audio signal decoder 100 will be described.
Subsequently, the structure of the audio signal decoder 100 will be described and, finally,
the functionality of the audio signal decoder 100 will be discussed.
The audio signal decoder 100 is configured to receive a downmix signal representation
110, which typically represents a plurality of audio object signals, for example, in the form
of a one-channel audio signal representation or a two-channel audio signal representation.
The audio signal decoder 100 also receives an object-related parametric information 112,
which typically describes the audio objects, which are included in the downmix signal
representation 110.
For example, the object-related parametric information 112 describes object levels of the
audio objects, which are represented by the downmix signal representation 110, using
object-level difference values (OLD).
In addition, the object-related parametric information 112 typically represents inter-object-
correlation characteristics of the audio objects, which are represented by the downmix
signal representation 110. The object-related parametric information typically comprises a
bitstream signalling parameter (also designated with "bsOnelOC" herein), which signals
whether the object-rated parametric information comprises individual inter-object-
correlation bitstream parameter values associated to individual pairs of audio objects or a
common inter-object-correlation bitstream parameter value associated with a plurality of
pairs of audio objects. Accordingly, the object-related parametric information comprises
the individual inter-object-correlation bitstream parameter values or the common inter-
object-correlation bitstream parameter value, in accordance with the bitstream signalling
parameter "bsOnelOC".

The object-related parametric information 112 may also comprise downmix information
describing a downmix of the individual audio objects into the downmix signal
representation. For example, the object-related parametric information comprises a
downmix gain information DMG describing a contribution of the audio object signals to
the downmix signal representation 110. In addition, the object-related parametric
information may, optionally, comprise a downmix-channel-level-difference information
DCLD describing downmix gain differences between different downmix channels.
The signal decoder 100 is also configured to receive a rendering information 120, for
example, from a user interface for inputting said rendering information. The rendering
information describes an allocation of the signals of the audio objects to upmix channels.
For example, the rendering information 120 may take the form of a rendering matrix (or
entries thereof). Alternatively, the rendering information 120 may comprise a description
of a desired rendering position (for example, in terms of spatial coordinates) of the audio
objects and desired intensities (or volumes) of the audio objects.
The audio signal decoder 100 provides an upmix signal representation 130, which
constitutes a rendered representation of the audio object signals described by the downmix
signal representation and the object-related parametric information. For example, the
upmix signal representation may take the form of individual audio channel signals, or may
take the form of a downmix signal representation in combination with a channel-related
parametric side information (for example, MPEG-Surround side information).
The audio signal decoder 100 is configured to provide the upmix signal representation 130
on the basis of the downmix signal representation 110 and the object-related parametric
information 112 and in dependence on the rendering information 120. The apparatus 100
comprises an object-parameter determinator 140, which is configured to obtain inter-
object-correlation values (at least) for a plurality of pairs of related audio objects on the
basis of the object-related parametric information 112. For this purpose, the object-
parameter determinator 140 is configured to evaluate the bitstream signalling parameter
("bsOnelOC") in order to decide whether to evaluate individual inter-object-correlation
bitstream parameter values to obtain the inter-object-correlation values for a plurality of
pairs of related audio objects or to obtain the inter-object-correlation values for a plurality
of pairs of related audio objects using a common inter-object-correlation bitstream
parameter value. Accordingly, the object-parameter determinator 140 is configured to
provide the inter-object-correlation values 142 for a plurality of pairs of related audio
objects on the basis of individual inter-object-correlation bitstream parameter values if the
bitstream signaling parameter indicates that a common inter-object-correlation bitstream

parameter value is not available. Similarly, the object-parameter determinator determines
the inter-object-correlation values 142 for a plurality of pairs of related audio objects on
the basis of the common inter-object-correlation bitstream parameter value if the bitstream
signaling parameter indicates that such a common inter-object-correlation bitstream
parameter value is available.
The object-parameter determinator also typically provides other object-related values, like,
for example, object-level-difference values OLD, downmix-gain values DMG and
(optionally) downmix-channel-level-difference values DCLD on the basis of the object-
related parametric information 112.
The audio signal decoder 100 also comprises an signal processor 150, which is configured
to obtain the upmix signal representation 130 on the basis of the downmix signal
representation 110 and using the inter-object-correlation values 142 for a plurality of pairs
of related audio objects and the rendering information 120. The signal processor 150 also
uses the other object-related values, like object-level-difference values, downmix-gain
values and downmix-channel-level-difference values.
The signal processor 150 may, for example, estimate statistic characteristics of a desired
upmix signal representation 130 and process the downmix signal representation such that
the upmix signal representation 130 derive from the downmix signal representation
comprises the desired statistic characteristics. Alternatively, the signal processor 150 may
try to separate the audio object signals of the plurality of audio objects, which are
combined in the downmix signal representation 110, using the knowledge about the object
characteristics and the downmix process. Accordingly, the signal processor may calculate a
processing rule (for example, a scaling rule or a linear combination rule), which would
allow for a reconstruction of the individual audio object signals or at least of audio signals
having similar statistical characteristics as the individual audio object signals. The signal
processor 150 may then apply the desired rendering to obtain the upmix signal
representation. Naturally, the computation of reconstructed audio object signals, which
approximate the original individual audio object signals, and the rendering can be
combined in a single processing step in order to reduce the computational complexity.
To summarize the above, the audio signal decoder is configured to provide the upmix
signal representation 130 on the basis of the downmix signal representation 110 and the
object-related parametric information 112 using the rendering information 120. The object-
related parametric information 112 is evaluated in order to have a knowledge about the
statistical characteristics of the individual audio object signals and of the relationship

between the individual audio object signals, which is required by the signal processor 150.
For example, the object-related parametric information 112 is used in order to obtain an
estimated variance matrix describing estimated covariance values of the individual audio
object signals. The estimated covariance matrix is then applied by the signal processor 150
in order to determine a processing rule (for example, as discussed above) for deriving the
upmix signal representation 130 from the downmix signal representation 110, wherein,
naturally, other object-related information may also be exploited.
The object-parameter determinator 140 comprises different modes in order to obtain the
inter-object-correlation values for a plurality of pairs of related audio objects, which
constitutes an important input information for the signal processor 150. In a first mode, the
inter-object-correlation values are determined using individual inter-object-correlation
bitstream parameter values. For example, there may be one individual inter-object-
correlation bitstream parameter value for each pair of related audio objects, such that the
object-parameter determinator 140 simply maps such an individual inter-object-correlation
bitstream parameter value onto one or two inter-object-correlation values associated with a
given pair of related audio objects. On the other hand, there is also a second mode of
operation, in which the object-parameter determinator 140 merely reads a single common
inter-object-correlation bitstream parameter value from the bitstream and provides a
plurality of inter-object-correlation values for a plurality of different pairs of related audio
objects on the basis of this single common inter-object-correlation bitstream parameter
value. Accordingly, the inter-object-correlation values for a plurality of pairs of related
audio objects may, for example, be identical to the value represented by the single common
inter-object-correlation bitstream parameter value, or may be derived from the same
common inter-object-correlation bitstream parameter value. The object-parameter
determinator 140 is switchable between said first mode and said second mode in
dependence on the bitstream signalling parameter ("bsOnelOC").
Accordingly, there are different modes for the provision of the inter-object-correlation
values, which can be applied by the object-parameter determinator 140. If there is a
relatively small number of pairs of related audio objects, the inter-object-correlation values
for said pairs of related audio objects are typically (in dependence on the bitstream
signaling parameter) determined individually by the object-parameter determinator, which
allows for a particularly precise representation of the characteristics of said pairs of related
audio objects and, consequently, brings along the possibility of reconstructing the
individual audio object signals with good accuracy in the signal processor 150. Thus, it is
typically possible to provide a good hearing impression in such a case in which only

correlations between a comparatively small number of pairs of related audio objects are
relevant.
The second mode of operation of the object-parameter determinator, in which a common
inter-object-correlation bitstream parameter value is used to obtain inter-object-correlation
values for a plurality of pairs of related audio objects, is typically used in cases in which
there are non-negligible correlations between a plurality of pairs of audio objects. Such
cases could conventionally not be handled without excessively increasing the bitrate of a
bitstream representing both the downmix signal representation 110 and the object-related
parametric information 112. The usage of a common inter-object-correlation bitstream
parameter value brings along specific advantages if there are non-negligible correlations
between a comparatively large number of pairs of audio objects, which correlations do not
comprise acoustically significant variations. In this case, it is possible to consider the
correlations with moderate bitrate effort, which brings along a reasonably good
compromise between bitrate requirement and quality of the hearing impression.
Accordingly, the audio signal decoder 100 is capable of efficiently handling different
situations, namely situations in which there are only a few pairs of related audio objects,
the inter-object-correlation of which should be taken into consideration with high
precision, and situations in which there is a large number of pairs of related audio objects,
the inter-object-correlations of which should not be neglected entirely but have some
similarity . The audio signal decoder 100 is capable of handling both situations with a good
quality of the hearing impression.
2. Audio Signal Encoder according to Fig. 2
In the following, an audio signal encoder 200 will be described taking reference to Fig. 2,
which shows a block schematic diagram of such an audio signal encoder 200.
The audio signal encoder 200 is configured to receive a plurality of audio object signals
210a to 210N. The audio object signals 210a to 210N may, for example, be one-channel
signals or two-channel signals representing different audio objects.
The audio signal encoder 200 is also configured to provide a bitstream representation 220,
which describes the auditory scene represented by the audio object signals 210a to 210N in
a compact and bitrate-efficient manner.

The audio signal encoder 200 comprises a downmixer 220, which is configured to receive
the audio object signals 210a to 210N and to provide a downmix signal 232 on the basis of
the audio object signals 210a to 210N. The downmixer 230 is configured to provide the
downmix signal 232 in dependence on downmix parameters describing contributions of the
audio object signals 210a to 210N to the one or more channels of the downmix signal.
The audio signal encoder also comprises a parameter provider 240, which is configured to
provide a common inter-object-correlation bitstream parameter value 242 associated with a
plurality of pairs of related audio object signals 210a to 210N. The parameter provider 240
is also configured to provide a bitstream signalling parameter 244 indicating that the
common inter-object-correlation bitstream parameter value 242 is provided instead of a
plurality of individual inter-object-correlation bitstream parameters (individually
associated with different pairs of audio objects).
The audio signal encoder 200 also comprises a bitstream formatter 250, which is
configured to provide a bitstream representation 250 comprising a representation of the
downmix signal 232 (for example, an encoded representation of the downmix signal 232),
a representation of the common inter-object-correlation bitstream parameter value 242 (for
example, a quantized and encoded representation thereof) and the bitstream signalling
parameter 244 (for example, in the form of a one-bit parameter value).
The audio signal decoder 200 consequently provides a bitstream representation 220, which
represents the audio scene described by the audio object signals 210a to 210N with good
accuracy. In particular, the bitstream representation 220 comprises a compact side
information if many of the audio object signals 210a to 210N are related to each other, i.e.
comprise a non-negligible inter-object-correlation. In this case, the common inter-object-
correlation bitstream parameter value 242 is provided instead of individual inter-object-
correlation bitstream parameter values individually associated with pairs of audio objects.
Accordingly, the audio signal encoder can provide a compact bitstream representation 220
in any case, both if there are many related pairs of audio object signals 210a to 210N and if
there are only a few pairs of related audio object signals 210a to 210N. In particular the
bitstream representation 220 may comprise the information required by the audio signal
decoder 100 as an input information, namely the downmix signal representation 110 and
the object-related parametric information 112. Thus, the parameter provider 240 may be
configured to provide additional object-related parametric information describing the audio
object signals 210a to 210N as well as the downmix process performed by the downmixer
230. For example, the parameter provider 240 may additionally provide an object-level-
difference information OLD describing the object levels (or object-level differences) of the

audio object signals 210a to 210N. Furthermore, the parameter provider 240 may provide a
downmix-gain information DMG describing downmix gains applied to the individual
audio object signals 210a to 210N when forming the one or more channels of the downmix
signal 232. Downmix-channel-level-difference values DCLD, which describe downmix
gain differences between different channels of the downmix signal 232, may also,
optionally, be provided by the parameter provider 240 for inclusion into the bitstream
representation 220.
To summarize the above, the audio signal encoder efficiently provides the object-related
parametric information required for a reconstruction of the audio scene described by the
audio object signals 210a to 210N with a good hearing impression, wherein a compact
common inter-object-correlation bitstream parameter value is used if there is a large
number of related pairs of audio objects. This is signaled using the bitstream signaling
parameter 244. Thus, an excessive bitstream load is avoided in such a case.
Further details regarding the provision of a bitstream representation will be described
below.
3. Bitstream according to Fig. 3
Fig. 3 shows a schematic representation of a bitstream 300, according to an embodiment of
the invention.
The bitstream 300 may, for example, serve as an input bitstream of the audio signal
decoder 100, carrying the downmix signal representation 110 and the object-related
parametric information 112. The bitstream 300 may be provided as an output bitstream 220
by the audio signal encoder 200.
The bitstream 300 comprises a downmix signal representation 310, which is a
representation of a one-channel or multi-channel downmix signal (for example, the
downmix signal 232) combining audio signals of a plurality of audio objects. The bitstream
300 also comprises object-related parametric side information 320 describing
characteristics of the audio objects, the audio object signals of which are represented, in a
combined form, by the downmix signal representation 310. The object-related parametric
side information 320 comprises a bitstream signaling parameter 322 indicating whether the
bitstream comprises individual inter-object-correlation bitstream parameters (individually
associated with different pairs of audio objects) or a common inter-object-correlation
bitstream parameter value (associated with a plurality of different pairs of audio objects).

The object-related parametric side information also comprises a plurality of individual
inter-object-correlation bitstream parameter values 324a, which is indicated by a first state
of the bitstream signaling parameter 322, or a common inter-object-correlation bitstream
parameter value, which is indicated by a second state of the bitstream signaling parameter
322.
Accordingly, the bitstream 300 may be adapted to the relationship characteristics of the
audio object signals 210a to 210N by adapting the format of the bitstream 300 to contain a
representation of individual inter-object-correlation bitstream parameter values or a
representation of a common inter-object-correlation bitstream parameter value.
The bitstream 300 may, consequently, provide the chance of efficiently encoding different
types of audio scenes with a compact side information, while maintaining the change of
obtaining a good hearing impression for the case that there are only a few strongly-
correlated audio objects.
Further details regarding the bitstream will subsequently be discussed.
4. The MPEG SAOC System according to Fig. 4
In the following, an MPEG SAOC system using a single IOC parameter calculation will be
described taking reference to Fig. 4.
The MPEG SAOC system 400 according to Fig. 4 comprises an SAOC encoder 410 and an
SAOC decoder 420.
The SAOC encoder 410 is configured to receive a plurality of, for example, L audio object
signals 420a to 420N. The SAOC encoder 410 is configured to provide a downmix signal
representation 430 and a side information 432, which are preferably, but not necessarily,
included in a bitstream.
The SAOC encoder 410 comprises an SAOC downmix processing 440, which receives the
audio object signals 420a to 420N and provides the downmix signal representation 430 on
the basis thereof. The SAOC encoder 410 also comprises a parameter extractor 444, which
may receive the object signals 420a to 420N and which may, optionally, also receive an
information about the SAOC downmix processing 440 (for example, one or more
downmix parameters). The parameter extractor 444 comprises a single inter-object-
correlation calculator 448, which is configured to calculate a single (common) inter-object-

correlation value associated with a plurality of pairs of audio objects. In addition, the single
inter-object-correlation calculator 448 is configured to provide a single inter-object-
correlation signaling 452, which indicates if a single inter-object-correlation value is used
instead of object-pair-individual inter-object-correlation values. The single inter-object-
correlation calculator 448 may, for example, decide on the basis of an analysis of the audio
object signals 420a to 420N whether a single common inter-object-correlation value (or,
alternatively, a plurality of individual inter-object-correlation parameter values associated
individually with pairs of audio object signals) are provided. However, the single inter-
object-correlation calculator 448 may also receive an external control information
determining whether a common inter-object-correlation value (for example, a bitstream
parameter value) or individual inter-object-correlation values (for example, bitstream
parameter values) should be calculated.
The parameter extractor 444 is also configured to provide a plurality of parameters
describing the audio object signals 420a to 420N, like, for example, object-level difference
parameters. The parameter extractor 444 is also preferably configured to provide
parameters describing the downmix, like, for example, a set of downmix-gain parameters
DMG and a set of downmix-channel-level-difference parameters DCLD.
The SAOC encoder 410 comprises a quantization 456, which quantizes the parameters
provided by the parameter extractor 444. For example, the common inter-object-correlation
parameter may be quantized by the quantization 456. In addition, the object-level-
difference parameters, the downmix-gain parameters and the downmix-channel-level-
difference parameters may also be quantized by the quantization 456. Accordingly, the
quantized parameters are obtained by the quantization 456.
The SAOC encoder 410 also comprises a noiseless coding 460, which is configured to
encode the quantized parameters provided by the quantization 456. For example, the
noiseless coding may noiselessly encode the quantized common inter-object-correlation
parameter and also the other quantized parameters (for example, OLD, DMG and DCLD).
Accordingly, the SAOC decoder 410 provides the side information 432 such that the side
information comprises the single IOC signaling 452 (which may be considered as a
bitstream signaling parameter) and the noiselessly-coded parameters provided by the
noiseless coding 480 (which may be considered as bitstream parameter values).

The SAOC decoder 420 is configured to receive the side information 432 provided by the
SAOC encoder 410 and the downmix signal representation 430 provided by the SAOC
encoder 410.
The SAOC decoder 420 comprises a noiseless decoding 464, which is configured to
reverse the noiseless coding 460 of the side information 432 performed in the encoder 410.
The SAOC decoder 420 also comprises a de-quantization 468, which may also be
considered as an inverse quantization (even though, strictly speaking, quantization is not
invertible with perfect accuracy), wherein the de-quantization 468 is configured to receive
the decoded side information 466 from the noiseless decoding 464. The de-quantization
468 provides the dequantized parameters 470, for example, the decoded and de-quantized
common inter-object-correlation value provided by the single inter-object-correlation
calculator 448 and also decoded and de-quantized object-level difference values OLD,
decoded and de-quantized downmix-gain values DMG and decoded and de-quantized
downmix-channel-level-difference values DCLD. The SAOC decoder 420 also comprises
a single inter-object-correlation expander 474, which is configured to provide a plurality of
inter-object-correlation values associated with a plurality of pairs of related audio objects
on the basis of the common inter-object-correlation value. However, it should be noted that
the single inter-object-correlation expander 474 may be arranged before the noiseless
decoding 464 and the de-quantization 468 in some embodiments. For example, the single
inter-object-correlation expander 474 may be integrated into a bitstream parser, which
receives a bitstream comprising both the downmix signal representation 430 and the side
information 432.
The SAOC decoder 420 also comprises an SAOC decoder processing and mixing 480,
which is configured to receive the downmix signal representation 430 and the decoded
parameters included (in an encoded form) in the side information 432. Thus, the SAOC
decoder processing and mixing 480 may, for example, receive one or two inter-object-
correlation values for every pair of (different) audio objects, wherein the one or two inter-
object-correlation values may be zero for non-related audio objects and non-zero for
related audio objects. In addition, the SAOC decoder processing and mixing 480 may
receive object-level-difference values for every audio object. In addition, the SAOC
decoder processing and mixing 480 may receive downmix-gain values and (optionally)
downmix-channel-level-difference values describing the downmix performed in the SAOC
downmix processing 440. Accordingly, the SAOC decoder processing and mixing 480
may provide a plurality of channel signals 484a to 484N in dependence on the downmix
signal representation 430, the side information parameters included in the side information
432 and an interaction information 482, which describes a desired rendering of the audio

objects. However, it should be noted that the channels 484a to 484N may be represented
either in the form of individual audio channel signals or in the form of a parametric
representation, like, for example, a multi-channel representation according to the MPEG
Surround standard (comprising, for example, an MPEG Surround downmix signal and
channel-related MPEG Surround side information). In other words, both an individual
channel audio signal representation and a parametric multi-channel audio signal
representation will be considered as an upmix signal representation within the present
description.
In the following, some details regarding the functionality of the SAOC encoder 410 and of
the SAOC decoder 420 will be described.
The SAOC side information, which will be discussed in the following, plays an important
role in the SAOC encoding and the SAOC decoding. The SAOC side information
describes the input objects (audio objects) by means of their time/frequency variant
covariance matrix. The N object signals 420a to 420N (also sometimes briefly designated
as "objects") can be written as rows in a matrix:

Here, the entries Si(l) designate spectral values of an audio object having audio object index
i for a plurality of temporal portions having time indices 1. A signal block of L samples
represents the signal in a time and frequency interval which is a part of the perceptually
motivated tiling of the time-frequency plane that is applied for the description of signal
properties.
Hence, the covariance matrix is given as


with

The covariance matrix is typically used by the SAOC decoder processing and mixing 480
in order to obtain the channel signals 484a to 484N.
The diagonal elements can directly be reconstructed at the SAOC decoder side with the
OLD data, and the non-diagonal elements are given by the inter-object-correlations (IOCs)
as

It should be noted that the object-level-difference values describe sm and sn.
The number of inter-object-correlation values needed to convey the whole covariance
matrix is N*N/2-N/2. As this number can get large (for example, for a large number N of
object signals), resulting in a high bit demand, the SAOC encoder 410 (as well as the audio
signal encoder 200) can, optionally, transmit only selected inter-object-correlation values
for object pairs, which are signaled to be "related to" each other. This optional "related to"
information is, for example, statically conveyed in an SAOC-specific configuration syntax
element of the bitstream, which may, for example, be designated with
"SAOCSpecificConfigO". Objects, which are not related to each other, are, for example,
assumed to be uncorrelated, i.e. their inter-object-correlation is equal to zero.
However, there exist application scenarios where all objects (or almost all objects) are
related to each other. An example of such an application scenario is a telephone conference
with a microphone setup and room acoustics with a high degree of inter-microphone cross
talk. In these cases, the transmission of all IOC values would be necessary (if the above-
mentioned conventional mechanism was used), but usually would exceed the desired bit
budget. As an alternative, assuming that all objects are uncorrelated would induce a large
error in the model and, therefore, would yield sub-optimal audio quality of the rendered
scene.
The underlying assumption of the proposed approach is that for certain SAOC application
scenarios, uncorrelated sound sources result in correlated SAOC input objects due to the
acoustic environment they are located in and due to the applied recording techniques.

Considering a telephone conference setup, for instance, the impact of the room
reverberation and the imperfect isolation of the individual speakers leads to correlated
SAOC objects although the talking of the individual subjects is uncorrelated. These
acoustical circumstances and the resulting correlation can be approximately described with
a single frequency- and time-varying value.
Thus, the proposed method successfully circumvents the high bitrate demand of conveying
all desired object correlations. This is done by calculating a single time/frequency
dependent single IOC value in a dedicated "single IOC calculator" module 448 in the
SAOC encoder (see Fig. 4). Use of the "single IOC" feature is signaled in the SAOC
information (for example, using the bitstream signaling parameter "bsOnelOC"). The
single IOC value per time/frequency tile is then transmitted instead of all separate IOC
values (for example, using the common inter-object-correlation bitstream parameter value).
In a typical application, the bitstream header (for example, the "SAOCSpecificConfigO"
element according to the non-prepublished SAOC Standard [SAOC]) includes one bit
indicating if "single IOC" signaling or "normal" IOC signaling is used. Some details
regarding this issue will be discussed below.
The payload frame data (for example, the "SAOCFrame()" element in the non-
prepublished SAOC Standard [SAOC]) then includes IOCs common for all objects or
several IOCs depending on the "single IOCs" or "normal" mode.
Hence, a bitstream parser (which may be part of the SAOC decoder) for the payload data
in the decoder could be designed according to the example below (which is formulated in a
pseudo C code):
if (iocMode == SINGLEJOC)
{
readIocDataFromBitstream(l);
}
else
{
readlocDataFromBitstream (numberOfTransmittedlocs);
}

According to the above example, the bitstream parser checks whether a flag "iocMode"
(also designated with "bsOnelOC" in the following) indicates that there is only a single
inter-object-correlation bitstream parameter value (which is signaled by the parameter
value "SINGLEIOC"). If the bitstream parser finds that there is only a single inter-object-
correlation value, the bitstream parser reads one inter-object-correlation data unit (i.e., one
inter-object-correlation bitstream parameter value) from the bitstream, which is indicated
by the operation "readlocDataFromBitstream(l)". If, in contrast, the bitstream parser finds
that the flag "iocMode" does not indicate the usage of a single (common) inter-object-
correlation value, the bitstream parser reads a different number of inter-object-correlation
data units (e.g., inter-object-correlation bitstream parameter values) from the bitstream,
which is indicated by the function "readlocDataFromBitstream
(numberOfTransmittedlocs)"). The number ("numberOfTransmittedlocs") of inter-object-
correlation data units read in this case is typically determined by a number of pairs of
related audio objects.
Alternatively, the "single IOC" signalling can be present in the payload frame (for
example, in the so-called "SAOCFrameO" element in the non-prepublished SAOC
Standard) to enable dynamical switching between single IOC mode and normal IOC mode
on a per-frame basis.
5. Encoder-Sided Implementation of the Calculation of a Common Inter-Object-
Correlation Bitstream Parameter
In the following, some preferred implementations for the single IOC (IOCSingie) calculation
will be described.
5.1. Calculation using Cross-Power Terms
In a preferred embodiment of the SAOC encoder 410, the common inter-object-correlation
bitstream parameter value IOCSjngie can be computed according to the following equation:


with the cross power terms

where n and k are the time and frequency instances (or time and frequency indices) for
which the SAOC parameter applies.
In other words, the common inter-object-correlation bitstream parameter value IOCSingie
can be computed in dependence on a ratio between a sum of cross-power terms nrgjj
(wherein the object index i is typically different from the object index j) and a sum of
average energy values (which average energy values represent, for example, a
geometrical mean between the energy values nrga and nrgjj).
The summation may be performed, for example, for all pairs of different audio objects, or
for pairs of related audio objects only.
The cross-power term nrgjj may, for example, be formed as a sum over complex conjugate
products (with one of the factors being complex-conjugated) of spectral coefficients Sjn',
Sjnk associated with the audio object signals of the pair of audio objects under
consideration for a plurality of time instances (having time indices n) and/or a plurality of
frequency instances (having frequency indices k).
A real part of said ratio may be formed (for example, by an operation Re{}) in order to
have a real-valued common inter-object-correlation bitstream parameter value IOCSjngie, as
shown in the above equation.
5.2. Usage of a Constant Value
In another preferred embodiment, a constant value c may be chosen to obtain the common
inter-object-correlation bitstream parameter value IOCSingie in accordance with
IOCsjngie — C,
with c being a constant.

This constant c could, for example, describe a time- and frequency-independent cross talk
of a room with specific acoustics (amount of reverb) where a telephone conference takes
place.
The constant c may, for example, be set in accordance with an estimation of the room
acoustics, which may be performed by the SAOC encoder. Alternatively, the constant c
may be input via a user interface, or may be predetermined in the SAOC encoder 410.
6. Decoder-Sided Determination of the Inter-object-correlation Values for all Object
Pairs
In the following, it will be described how the inter-object-correlation values for all object
pairs can be obtained.
At the decoder side (for example, in the SAOC decoder 420), the single inter-object-
correlation (bitstream) parameter (IOCSingie) is used to determine the inter-object-
correlation values for all object pairs. This is done, for example, in the "Single IOC
Expander" module 474 (see Fig. 4).
A preferred method is a simple copy operation. The copying can be applied with or without
considering the "related to" information conveyed, for example, in the SAOC bitstream
header (for example, in the portion "SAOCSpecificConfiguration()").
In a preferred embodiment, a copying without "related to" information (i.e., without
transferring or considering a "related to" information) may be performed in the following
manner:
for all m, n with m ^ n.
Thus, all inter-object-correlation values for pairs of different audio objects are set to the
common inter-object-correlation (bitstream) parameter value.
In another preferred embodiment, a copying with "related to" information (i.e., taking into
consideration the "related to" information) is performed, for example, in the following
manner:


Accordingly, one or even two inter-object-correlation values associated with a pair of
audio objects (having audio object indices m and n) are set to the value IOCSingie specified,
for example, by the common inter-object-correlation bitstream parameter value, if the
object relationship information "relatedTo(m,n)" indicates that said audio objects are
related to each other. Otherwise, i.e. if the object relationship information "relatedTo(m,n)"
indicates that the audio objects of a pair of audio objects are not related, one or even two
inter-object-correlation values associated with the pair of audio objects are set to a
predetermined value, for example, to zero.
However, different distribution methods are possible, for example, taking the object
powers into account. For example, inter-object-correlation values relating to objects with
relatively low power could be set to high values, such as 1 (full correlation), to minimize
the influence of the decorrelation filter in the SAOC decoder.
7. Decoder Concept using Bitstream Elements according to Figs. 5 and 6
In the following, a decoder concept of an audio signal decoder using the bitstream syntax
elements according to Figs. 5 and 6 will be described. It should be noted here that the
bitstream syntax and bitstream evaluation concept, which will be described with reference
to Figs. 5 and 6, can be applied, for example, in the audio signal decoder 100 according to
Fig. 1 and in the audio signal decoder 420 according to Fig. 4. In addition, it should be
noted that the audio signal encoder 200 according to Fig. 2 and the audio signal decoder
410 according to Fig. 4 can be adapted to provide bitstream syntax elements as discussed
with respect to Figs. 5 and 6.
Accordingly, the bitstream comprising the downmix signal representation 110 and the
object-related parametric information 112 and/or the bitstream representation 220 and/or
the bitstream 300 and/or a bitstream comprising the downmix information 430 and the side
information 432, may be provided in accordance with the following description.
An SAOC bitstream, which may be provided by the above-described SAOC encoders and
which may be evaluated by the above-described SAOC decoders may comprise an SAOC
specific configuration portion, which will be described in the following taking reference to
Fig. 5, which shows a syntax representation of such an SAOC specific configuration
portion "SAOCSpecificConfigQ".

The SAOC specific configuration information comprises, for example, sampling frequency
configuration information, which describes a sampling frequency used by an audio signal
encoder and/or to be used by an audio signal decoder. The SAOC specific configuration
information also comprises a low delay mode configuration information, which describes
whether a low delay mode has been used by an audio signal encoder an/or should be used
by an audio signal decoder. The SAOC specific configuration information also comprises a
frequency resolution configuration information, which describes a frequency resolution
used by an audio signal encoder and/or to be used by an audio signal decoder. The SAOC
specific configuration information also comprises a frame length configuration information
describing a frame length of audio frames used by the SAOC encoder and/or to be used by
the SAOC decoder. The SOAC specific configuration information also comprises an object
number configuration information which describes a number of audio objects. This object
number configuration information, which is also designated with "bsNumObjects", for
example describes the value N, which has been used above.
The SAOC specific configuration information also comprises an object relationship
configuration information. For example, there may be one bitstream bit for every pair of
different audio objects. However, the relationship of audio objects may be represented, for
example, by a square N x N matrix having a one-bit entry for every combination of audio
objects. Entries of said matrix describing the relationship of an object with itself, i.e.,
diagonal elements, may be set to one, which indicates that an object is related to itself.
Two entries, namely a first entry having a first index i and a second index j, and a second
entry having a first index j and a second index i, may be associated with each pair of
different audio objects having audio object indices i and j. Accordingly, a single bitstream
bit determines the values of two entries of the object relationship matrix, which are set to
identical values.
As can be seen, a first audio object index i runs from i = 0 to i = bsNumObjects (outer for-
loop). A diagonal entry "bsRelatedTo[i][i]" is set to one for all values of i. For a first audio
object index i, bits describing a relationship between audio object i and audio objects j
(having audio object index j) are included in the bit stream for j = i + 1 to j =
bsNumObjects. Accordingly, entries of the relationship matrix "bsRelatedTo[i][j]", which
describe a relationship between the audio objects having audio object indices i and j, are
set to the value given in the bit stream. In addition, an object relationship matrix entry
"bsRelatedTo[j][i]" is set to the same value, i.e., to the value of the matrix entry
"bsRelatedTo[i][j]". For details, reference is made to the syntax representation of Fig. 5.

The SAOC specific configuration information also comprises an absolute energy
transmission configuration information, which describes whether an audio encoder has
included an absolute energy information into the bit stream, and/or whether an audio
decoder should evaluate an absolute energy transmission configuration information
included in the bit stream.
The SAOC specific configuration information also comprises a downmix-channel-number
configuration information, which describes a number of downmix channels used by the
audio encoder and/or to be used by the audio decoder. The SAOC specific configuration
information may also comprise additional configuration information, which is not relevant
for the present application, and which can optionally be omitted.
The SAOC specific configuration information also comprises a common inter-object-
correlation configuration information (also designated as a "bitstream signaling parameter"
herein) which describes whether a common inter-object-correlation bitstream parameter
value is included in the SAOC bitstream, or whether object-pair-individual inter-object-
correlation bitstream parameter values are included in the SAOC bitstream. Said common
inter-object-correlation configuration information may, for example, be designated with
"bsOnelOC, and may be a one-bit value.
The SAOC specific configuration information may also comprise a distortion control unit
configuration information.
In addition, the SAOC specific configuration information may comprise one or more fill
bits, which are designated with "ByteAlignQ", and which may be used to adjust the lengths
of the SAOC specific configuration information. In addition, the SAOC specific
configuration information may comprise optional additional configuration information
"SAOCExtensionConfigO" which is not of relevance for the present application and which
will not be discussed here for this reason.
It should be noted here that the SAOC specific configuration information may comprise
more or less than the above described configuration information. In other words, some of
the above described configuration information may be omitted in some embodiments, and
additional configuration information may also be also included in some embodiments.
However, it should be noted that the SAOC specific configuration information may, for
example, be included once per piece of audio in an SAOC bitstream. However, the SAOC
specific configuration information may optionally be included more often in the bitstream.

Nevertheless, the SAOC specific configuration information is typically provided for a
plurality of SAOC frames, because the SAOC specific configuration information provides
a significant bit load overhead.
In the following, the syntax of an SAOC frame will be described taking reference to Fig. 6,
which shows a syntax representation of such an SAOC frame. The SAOC frame comprises
encoded object-level-difference values OLD, which may be included band-wise and per
audio object.
The SAOC frame also comprises encoded absolute energy values NRG, which may be
considered as optional, and which may be included band-wise.
The SAOC frame also comprises encoded inter-object-correlation values IOC, which may
be provide band-wise, i.e., separately for a plurality of frequency bands, and for a plurality
of combinations of audio objects.
In the following, the bitstream will be described with respect to the operations which may
be performed by a bitstream parser parsing the bitstream.
The bitstream parser may, for example, initialize variables k, iocldxl, iocldx2 to a value of
zero in a first preparatory step.
Subsequently, the bitstream parser may perform a parsing for a plurality of values of the
first audio object index i between i = 0 and i = bsNumObjects (outer for-loop). The
bitstream parser may, for example, set an inter-object-correlation index value idxIoc[i][i]
describing a relationship between the audio object having audio object index i and itself to
zero which indicates a full correlation.
Subsequently, a bitstream parser may evaluate the bitstream for values j of a second audio
object index between i + 1 and bsNumObjects. If audio objects having audio object indices
i and j are related, which is indicated by a non-zero value of the object relationship matrix
entry "bsRelatedTo[i][j]", the bitstream parser performs an algorithm 610, and otherwise,
the bitstream parser sets the inter-object-correlation index associated with the audio objects
having audio object indices i and j to five (operation "idxIOC[i][j] = 5"), which describes a
zero correlation. Thus, for pairs of audio objects, for which the object relationship matrix
indicates no relationship, the inter-object-correlation value is set to zero. For related pairs
of audio objects, however, the bitstream signaling parameter "bsOnelOC", which is
included in the SAOC specific configuration, is evaluated to decide how to proceed. If the

bitstream signaling parameter "bsOnelOC" indicates that there are object-pair-individual
inter-object-correlation bitstream parameter values, a plurality of inter-object-relationship
indices idxIOC[i][j] (which may be considered as inter-object-relationship bitstream
parameter values) are extracted from the bitstream for "numBands" frequency bands using
the function "EcDataSaoc", wherein said function may be used to decode the inter-object-
relationship indices.
However, if the bitstream signaling parameter "bsOnelOC" indicated that a common inter-
object-correlation bitstream parameter value is used for a plurality of pairs of audio
objects, and id the bitstream parameter "bsRelatedTo[i][j]" indicates that the audio objects
having audio object indices i and j are related, a single set of a plurality of inter-object-
correlation indices "idxIOC[i][j]" is read from the bitstream using the function
"EcDataSaoc" for a plurality of numBands frequency bands, wherein only a single inter-
object-correlation index is read for any given frequency band. However upon re-execution
of the algorithm 610, a previously read inter-object-correlation index
idxIOC[iocldxl][iocldx2] is copied without evaluating the bitstream. This is ensured by
use of the variable k, which is initialized to zero and incremented upon evaluation of the
first set of inter-object-correlation indices idxIOC[i][j].
To summarize, for each combination of two audio objects, it is first evaluated whether the
two audio objects of such a combination are signaled as being related to each other (for
example, by checking whether the value ubsRelatedTo[i][j]" takes the value zero or not). If
the audio objects of the pair of audio objects are related, the further processing 610 is
performed. Otherwise, the value "idxIOC[i][j]" associated to this pair of (substantially
unrelated) audio objects is set to a predetermined value, for example, to a predetermined
value indicating a zero inter-object-correlation.
In the processing 610, a bitstream value is read from the bitstream for every pair of audio
objects (which is signaled to comprise related audio objects) if the signaling "bsOnelOC"
is inactive. Otherwise, i.e., if the signaling "bsOnelOC" is active, only one bitstream value
is read for one pair of audio objects, and the reference to said single pair is maintained by
setting the index values iocldxl and ioddx2 to point at this read out value. The single read
out value is reused for other pairs of audio objects (which are signaled as being related to
each other) if the signaling "bsOnelOC" is active.
Finally, it is also ensured that a same inter-object-correlation index value is associated to
both combinations of two given different audio objects, irrespective of which of the two

given audio objects is the first audio object and which of the two given audio objects is the
second audio object.
In addition, it should be noted that the SAOC frame typically comprises the encoded
downmix gain values (DMG) on a per-audio-object basis.
In addition, the SAOC frame typically comprises encoded downmix-channel-level-
differences (DCLD), which may optionally be included on a per-audio-object basis.
The SAOC frame further optionally comprises encoded post-processing-downmix-gain
values (PDG), which may be included in a band wise-manner and per downmix channel.
In addition, the SAOC frame may comprise encoded distortion-control-unit parameters,
which determine the application of distortion control measures.
Moreover, the SAOC frame may comprise one or more fill bits "ByteAlign()".
Furthermore, an SAOC frame may comprise extension data "SAOCExtensionFrame()'which, however, are not relevant for the present application and will not be discussed in
detail here for this reason.
Taking reference now to Fig. 7, an example for an advantageous quantization of the inter-
object-correlation parameter will be described.
As can be seen, a first row 710 of a table of Fig. 7 describes the quantization index idx,
which is in a range between zero and seven. This quantization index may be allocated to
the variable "idxIOC[i][j]". A second row 720 of the table of Fig. 7 shows the associated
inter object correlation value, and are in a range between -0.99 and 1. Accordingly, the
values of the parameters "idxIOC[i][j]" may be mapped onto inversely quantized inter-
object-correlation values using the mapping of the table of Fig. 7.
To conclude, an SAOC configuration portion "SAOCSpecificConfigO" preferably
comprises a bitstream parameter "bsOnelOC" which indicates if only a single IOC
parameter is conveyed common to all objects which have relation with each other, signaled
by "bsRelatedTo[i][j] =1". The inter-object-correlation values are included in the bitstream
in encoded form "EcDataSaoc (IOC,k,numBands)". An array "idxIOC[i][j]" is filled on the
basis of one or more encoded inter-object-correlation values. The entries of the array
"idxIOC[i][j]" are mapped onto inversely quantized values using the mapping table of Fig.

7, to obtain inversely quantized inter-object-correlation values. The inversely quantized
inter-object-correlation values, which are designated with IOCij, are used to obtain entries
of a covariance matrix. For this purpose, inversely quantized object-level-difference
parameters are also applied, which are designated with OLDj.
The covariance matrix E of size N x N with elements etj represents an approximation of
the original signal covariance matrix E « SS* and is obtained from the OLD and IOC
parameters as

7. Implementation Alternatives
Although some aspects have been described in the context of an apparatus, it is clear that
these aspects also represent a description of the corresponding method, where a block or
device corresponds to a method step or a feature of a method step. Analogously, aspects
described in the context of a method step also represent a description of a corresponding
block or item or feature of a corresponding apparatus. Some or all of the method steps may
be executed by (or using) a hardware apparatus, like for example, a microprocessor, a
programmable computer or an electronic circuit. In some embodiments, some one or more
of the most important method steps may be executed by such an apparatus.
The inventive encoded audio signal can be stored on a digital storage medium or can be
transmitted on a transmission medium such as a wireless transmission medium or a wired
transmission medium such as the Internet.
Depending on certain implementation requirements, embodiments of the invention can be
implemented in hardware or in software. The implementation can be performed using a
digital storage medium, for example a floppy disk, a DVD, a Blu-Ray, a CD, a ROM, a
PROM, an EPROM, an EEPROM or a FLASH memory, having electronically readable
control signals stored thereon, which cooperate (or are capable of cooperating) with a
programmable computer system such that the respective method is performed. Therefore,
the digital storage medium may be computer readable.

Some embodiments according to the invention comprise a data carrier having
electronically readable control signals, which are capable of cooperating with a
programmable computer system, such that one of the methods described herein is
performed.
Generally, embodiments of the present invention can be implemented as a computer
program product with a program code, the program code being operative for performing
one of the methods when the computer program product runs on a computer. The program
code may for example be stored on a machine readable carrier.
Other embodiments comprise the computer program for performing one of the methods
described herein, stored on a machine readable carrier.
In other words, an embodiment of the inventive method is, therefore, a computer program
having a program code for performing one of the methods described herein, when the
computer program runs on a computer.
A further embodiment of the inventive methods is, therefore, a data carrier (or a digital
storage medium, or a computer-readable medium) comprising, recorded thereon, the
computer program for performing one of the methods described herein. The data carrier,
the digital storage medium or the recorded medium are typically tangible and/or non-
trans itionary.
A further embodiment of the inventive method is, therefore, a data stream or a sequence of
signals representing the computer program for performing one of the methods described
herein. The data stream or the sequence of signals may for example be configured to be
transferred via a data communication connection, for example via the Internet.
A further embodiment comprises a processing means, for example a computer, or a
programmable logic device, configured to or adapted to perform one of the methods
described herein.
A further embodiment comprises a computer having installed thereon the computer
program for performing one of the methods described herein.
In some embodiments, a programmable logic device (for example a field programmable
gate array) may be used to perform some or all of the functionalities of the methods
described herein. In some embodiments, a field programmable gate array may cooperate

with a microprocessor in order to perform one of the methods described herein. Generally,
the methods are preferably performed by any hardware apparatus.
The above described embodiments are merely illustrative for the principles of the present
invention. It is understood that modifications and variations of the arrangements and the
details described herein will be apparent to others skilled in the art. It is the intent,
therefore, to be limited only by the scope of the impending patent claims and not by the
specific details presented by way of description and explanation of the embodiments
herein.

8. References
[BCC] C. Faller and F. Baumgarte, "Binaural Cue Coding - Part II: Schemes and
applications," IEEE Trans, on Speech and Audio Proc, vol. 11, no. 6, Nov. 2003
[JSC] C. Faller, "Parametric Joint-Coding of Audio Sources", 120th AES Convention,
Paris, 2006, Preprint 6752
[SAOC1] J. Herre, S. Disch, J. Hilpert, O. Hellmuth: "From SAC To SAOC - Recent
Developments in Parametric Coding of Spatial Audio", 22nd Regional UK AES
Conference, Cambridge, UK, April 2007
[SAOC2] J. Engdegard, B. Resch, C. Falch, O. Hellmuth, J. Hilpert, A. Holzer, L.
Terentiev, J. Breebaart, J. Koppens, E. Schuijers and W. Oomen: " Spatial Audio Object
Coding (SAOC) - The Upcoming MPEG Standard on Parametric Object Based Audio
Coding", 124th AES Convention, Amsterdam 2008, Preprint 7377
[SAOC] ISO/IEC, "MPEG audio technologies - Part 2: Spatial Audio Object
Coding (SAOC)," ISO/IEC JTC1/SC29/WG11 (MPEG) FCD 23003-2.

We Claim:
1. An audio signal decoder (100; 420) for providing an upmix signal representation
(130; 484a to 484M) on the basis of a downmix signal representation (110; 430)
and an object-related parametric information (112; 432), and depending on a
rendering information (120; 482), the apparatus comprising:
an object parameter determinator (140; 464, 468, 474) configured to obtain inter-
object-correlation values (142; IOCij) for a plurality of pairs of audio objects,
wherein the object parameter determinator is configured to evaluate a bitstream
signaling parameter (bsOnelOC) in order to decide whether to evaluate individual
inter-object-correlation bitstream parameter values, to obtain inter-object-
correlation values for a plurality of pairs of related audio objects, or to obtain inter-
object-correlation values for a plurality of pairs of related audio objects using a
common inter-object-correlation bitstream parameter value; and
a signal processor (150; 480) configured to obtain the upmix signal representation
on the basis of the downmix signal representation and using the inter-object-
correlation values for a plurality of pairs of related audio objects and the rendering
information;
wherein the object-related parametric information (112;432) comprises the
bitstream signaling parameter (bsOnelOC) and the individual inter-object-
correlation bitstream parameter values or the common inter-object-correlation
bitstream parameter value;
wherein the object parameter determinator (140; 464, 468, 474) is configured to
evaluate an object-relationship-information (bsRelatedTo), describing whether two
audio objects are related to each other; and
wherein the object parameter determinator is configured to selectively obtain inter-
object-correlation values for pairs of audio objects, for which the object-
relationship-information indicates a relationship, using the common inter-object-
correlation bitstream parameter value and to set inter-object-correlation values for

pairs of audio objects, for which the object-relationship information indicates no
relationship, to a predefined value.
2. The audio decoder according to claim 1, wherein the object parameter determinator
(140; 464, 468, 474) is configured to evaluate the object-relationship information
comprising a one-bit flag for each combination of different audio objects, wherein
the one-bit flag associated to a given combination of different audio objects
indicates whether the audio objects of the given combination are related or not.
3. The audio decoder according to one of claims 1 to 2, wherein the object parameter
determinator (140; 464, 468, 474) is configured to set the inter-object-correlation
value for all pairs of different related audio objects to a common value defined by
the common inter-object-correlation bitstream parameter value, or to a value
derived from the common value defined by the common inter-object-correlation
bitstream parameter value.
4. The audio decoder according to one of claims 1 to 3, wherein the object parameter
determinator (140; 464, 468, 474) comprises a bitstream parser configured to parse
a bitstream representation of an audio content, to obtain the bitstream signaling
parameter (bsOneIOC) and the individual inter-object-correlation bitstream
parameter values or the common inter-object-correlation bitstream parameter value.
5. The audio decoder according to one of claims 1 to 4, wherein the audio signal
decoder is configured to combine an inter-object-correlation value IOCij associated
with a pair of related audio objects with an object level difference value OLDi
describing an object level of a first audio object of the pair of related audio objects
and with an object level difference value OLDj describing an object level of a
second audio object of the pair of related audio objects, to obtain a covariance value
eij associated with the pair of related audio objects;
wherein the audio decoder is configured to obtain an element eij of a covariance
matrix according to
6. The audio signal decoder according to one of claims 1 to 5, wherein the audio
signal decoder is configured to handle three or more audio objects; and

wherein the object parameter determinator (140; 464, 468, 474) is configured to
provide an inter-object-correlation value for every pair of different audio objects.
7. The audio signal decoder according to one of claims 1 to 6, wherein the object
parameter determinator (140; 464, 468, 474) is configured to evaluate the bitstream
signaling parameter, which is included in a configuration bitstream portion
(SAOCSpecificConfig), in order to decide whether to evaluate the individual inter-
object-correlation bitstream parameter values to obtain the inter-object-correlation
values for a plurality of pairs of related audio objects, or to obtain the inter-object-
correlation values for a plurality of pairs of related audio objects using the common
inter-object-correlation bitstream parameter value; and
wherein the object parameter determinator is configured to evaluate an object
relationship information (bsRelatedTo[i][j]), which is included in the configuration
bitstream portion, to determine whether two audio objects are related; and
wherein the object parameter determinator is configured to evaluate a common
inter-object-correlation bitstream parameter value, which is included in a frame
data bitstream portion (SAOCFrame) for every frame of the audio content, if it is
decided to obtain inter-object-correlation values for a plurality of pairs of related
audio objects using a common inter-object-correlation bitstream parameter value.
8. An audio signal encoder (200; 410) for providing a bitstream representation on the
basis of a plurality of audio object signals (210a to 210N, 420a to 420N), the audio
signal encoder comprising:
a downmixer (230; 440) configured to provide a downmix signal (232; 430) on the
basis of the audio object signals and in dependence on downmix parameters (DMG,
DCLD) describing contributions of the audio object signals to one or more channels
of the downmix signal; and
a parameter provider (240; 444, 450, 460) configured to provide a common inter-
object-correlation bitstream parameter value (242) associated with a plurality of
pairs of related audio object signals, and to also provide a bitstream signaling
parameter (bsOnelOC; 244; 452) indicating that the common inter-object-
correlation bitstream parameter value is provided instead of a plurality of individual
inter-object-correlation bitstream parameter values;

wherein the parameter provider is configured to also provide an object relationship
information (bsRelatedTo) describing whether two audio objects are related to each
other; and
a bitstream formatter (250) configured to provide a bitstream comprising a
representation of the downmix signal, a representation of the common inter-object-
correlation bitstream parameter value and the bitstream signaling parameter.
9. The audio signal encoder according to claim 8, wherein the parameter provider is
configured to provide the common inter-object-correlation bitstream parameter
value in dependence on a ratio between a sum of cross power terms and a sum of
average power terms.
10. The audio signal encoder according to claim 9, wherein the parameter provider is
configured to compute the cross power term for a given pair of audio objects by
evaluating a sum of products of spectral coefficients associated with the audio
objects of the given pair of audio objects over a plurality of time instances, or over
a plurality of frequency instances; and
wherein the parameter provider is configured to compute the average power term
for a given pair of audio objects by evaluating a geometric mean of a power value
representing the power of a first audio object over a plurality of time instances or
over a plurality of frequency instances, and of a power value representing the power
of a second audio object over a plurality of time instances or over a plurality of
frequency instances.
11. The audio signal encoder according to claim 9 or claim 10, wherein the parameter
provider is configured to provide a common inter-object-correlation bitstream
parameter value IOCsingle according to


wherein,

wherein n and k describe time and frequency instances for which an SAOC
parameter applies; and
wherein Sin,k is a spectral value associated with time instance n and frequency
instance k of the audio object having audio object index i;
wherein Sjnk is a spectral value associated with time instance n and frequency
instance k of the audio object having audio object index j;
wherein N designates a total number of audio objects.
12. The audio signal encoder according to claim 8, wherein the parameter provider is
configured to provide a predetermined constant value as the common inter-object-
correlation bitstream parameter value.
13. The audio signal encoder according to one of claims 8 to 12, wherein the parameter
provider is configured to selectively evaluate an inter-object-correlation of audio
objects, for which the object relationship information indicates a relationship, for a
computation of the common inter-object-correlation bitstream parameter value.
14. A method for providing an upmix signal representation on the basis of a downmix
signal representation and an object-related parametric information and in
dependence on a rendering information, the method comprising:
obtaining inter-object-correlation values for a plurality of pairs of audio objects,
wherein a bitstream signaling parameter is evaluated in order to decide whether to
evaluate individual inter-object-correlation bitstream parameter values, to obtain
inter-object-correlation values for a plurality of pairs of related audio objects, or to
obtain inter-object-correlation values for a plurality of pairs of related audio objects
using a common inter-object-correlation bitstream parameter value; and

obtaining the upmix signal representation on the basis of the downmix signal
representation and using the inter-object-correlation values for a plurality of pairs
of related audio objects and the rendering information;
wherein an object-relationship information (bsRelatedTo), describing whether two
audio objects are related to each other, is evaluated, and
wherein the inter-object-correlation values are selectively obtained for pairs of
audio objects, for which the object relationship-information indicates a relationship,
using the common inter-object-correlation bitstream parameter value, and
wherein the inter-object-correlation values are set to a predefined value for pairs of
audio objects, for which the object-relationship information indicates no
relationship; and
wherein the object-related parametric information comprises the bitstream signaling
parameter (bsOnelOC) and the individual inter-object-correlation bitstream
parameter values or the common inter-object-correlation bitstream parameter value.
15. A method for providing a bitstream representation on the basis of a plurality of
audio object signals, the method comprising:
providing a downmix signal on the basis of the audio object signals and in
dependence on downmix parameters describing contributions of the audio object
signals to the one or more channels of the downmix signal; and
providing a common inter-object-correlation bitstream parameter value associated
with a plurality of pairs of related audio object signals; and
providing a bitstream signaling parameter indicating that the common inter-object-
correlation bitstream parameter value is provided instead of a plurality of individual
inter-object-correlation bitstream parameter values; and
providing an object-relationship information describing whether two audio objects
are related to each other,

providing a bitstream comprising a representation of the downmix signal, a
representation of the common inter-object-correlation bitstream parameter value
and the bitstream signaling parameter.
16. A computer program for performing the method according to claim 14 or claim 15
when the computer program runs on a computer.
17. A bitstream representing a multi-channel audio signal, the bitstream comprising:
a representation of a downmix signal combining audio signals of a plurality of
audio objects; and
an object-related parametric side information describing characteristics of the audio
objects, wherein the object-related parametric side information comprises a
bitstream signaling parameter indicating whether the bitstream comprises individual
inter-object-correlation bitstream parameter values or a common inter-object-
correlation bitstream parameter value, and an object-relationship information
describing whether two audio objects are related to each other.
18. An audio signal decoder (100; 420) for providing an upmix signal representation
(130; 484a to 484M) on the basis of a downmix signal representation (110; 430)
and an object-related parametric information (112; 432), and depending on a
rendering information (120; 482), the apparatus comprising:
an object parameter determinator (140; 464, 468, 474) configured to obtain inter-
object-correlation values (142; IOCij) for a plurality of pairs of audio objects,
wherein the object parameter determinator is configured to evaluate a bitstream
signaling parameter (bsOneIOC) in order to decide whether to evaluate individual
inter-object-correlation bitstream parameter values, to obtain inter-object-
correlation values for a plurality of pairs of related audio objects, or to obtain inter-
object-correlation values for a plurality of pairs of related audio objects using a
common inter-object-correlation bitstream parameter value; and
a signal processor (150; 480) configured to obtain the upmix signal representation
on the basis of the downmix signal representation and using the inter-object-

correlation values for a plurality of pairs of related audio objects and the rendering
information;
wherein the audio signal decoder is configured to combine an inter-object-
correlation value IOCij associated with a pair of related audio objects with an object
level difference value OLD; describing an object level of a first audio object of the
pair of related audio objects and with an object level difference value OLDj
describing an object level of a second audio object of the pair of related audio
objects, to obtain a covariance value eij associated with the pair of related audio
objects;
wherein the audio decoder is configured to obtain an element eij of a covariance
matrix according to
19. A method for providing an upmix signal representation on the basis of a downmix
signal representation and an object-related parametric information and in
dependence on a rendering information, the method comprising:
obtaining inter-object-correlation values for a plurality of pairs of audio objects,
wherein a bitstream signaling parameter is evaluated in order to decide whether to
evaluate individual inter-object-correlation bitstream parameter values, to obtain
inter-object-correlation values for a plurality of pairs of related audio objects, or to
obtain inter-object-correlation values for a plurality of pairs of related audio objects
using a common inter-object-correlation bitstream parameter value; and
obtaining the upmix signal representation on the basis of the downmix signal
representation and using the inter-object-correlation values for a plurality of pairs
of related audio objects and the rendering information;
wherein an inter-object-correlation value IOCij associated with a pair of related
audio objects is combined with an object level difference value OLDi describing an
object level of a first audio object of the pair of related audio objects and with an
object level difference value OLDj describing an object level of a second audio
object of the pair of related audio objects, to obtain a covariance value eij
associated with the pair of related audio objects;

wherein an element eij of a covariance matrix is obtained according to

ABSTRACT
An audio signal decoder for providing an upmix signal representation on the basis of a
downmix signal representation and an object-related parametric information and in
dependence on a rendering information comprises an object parameter determinator. The
object parameter determinator is configured to obtain inter-object-correlation values for a
plurality of pairs of audio objects. The object parameter determinator is configured to
evaluate a bitstream signaling parameter in order to decide whether to evaluate individual
inter-object-correlation bitstream parameter values to obtain inter-object-correlation values
for a plurality of pairs of related audio objects, or to obtain inter-object-correlation values
for a plurality of pairs of related audio objects using a common inter-object-correlation
bitstream parameter value. The audio signal decoder also comprises a signal processor
configured to obtain the upmix signal representation on the basis of the downmix signal
representation and using the inter-object-correlation values for a plurality of pairs of
related objects and the rendering information.