Apparatus and Method for Multi-Channel Parameter
Transformation
Field of the Invention
The present invention relates to a transformation of multi-channel
parameters, and in particular to the generation of
coherence parameters and level parameters, which indicate
spatial properties between two audio signals, based on an
object-parameter based representation of a spatial audio
scene.
Background of the Invention and Prior Art
There are several approaches for parametric coding of
multi-channel audio signals, such as 'Parametric Stereo
(PS)', 'Binaural Cue Coding (BCC) for Natural Rendering'
and 'MPEG Surround', which aim at representing a multi-channel
audio signal by means of a down-mix signal (which
could be either monophonic or comprise several channels)
and parametric side information ('spatial cues')
characterizing its perceived spatial sound stage.
Those techniques could be called channel-based, i.e. the
techniques try to transmit a multi-channel signal already
present or generated in a bitrate-efficient manner. That
is, a spatial audio scene is mixed to a predetermined
number of channels before transmission of the signal to
match a predetermined loudspeaker set-up and those
techniques aim at the compression of the audio channels
associated to the individual loudspeakers.
The parametric coding techniques rely on a down-mix channel
carrying audio content together with parameters, which
describe the spatial properties of the original spatial
audio scene and which are used on the receiving side to

reconstruct the multi-channel signal or the spatial audio
scene.
A closely related group of techniques, e.g. 'BCC for
Flexible Rendering', are designed for efficient coding of
individual audio objects rather than channels of the same
multi-channel signal for the sake of interactively
rendering them to arbitrary spatial positions and
independently amplifying or suppressing single objects
without any a priori encoder knowledge thereof. In contrast
to common parametric multi-channel audio coding techniques
(which convey a given set of audio channel signals from an
encoder to a decoder), such object coding techniques allow
rendering of the decoded objects to any reproduction setup,
i.e. the user on the decoding side is free to choose a
reproduction setup (e.g. stereo, 5.1 surround) according to
his preference.
Following the object coding concept, parameters can be
defined, which identify the position of an audio object in
space, to allow for flexible rendering on the receiving
side. Rendering at the receiving side has the advantage,
that even non-ideal loudspeaker set-ups or arbitrary
loudspeaker set-ups can be used to reproduce the spatial
audio scene with high quality. In addition, an audio
signal, such as, for example, a down-mix of the audio
channels associated with the individual objects, has to be
transmitted, which is the basis for the reproduction on the
receiving side.
Both discussed approaches rely on a multi-channel speaker
set-up at the receiving side, to allow for a high-quality
reproduction of the spatial impression of the original
spatial audio scene.
As previously outlined, there are several state-of-the-art
techniques for parametric coding of multi-channel audio
signals which are capable of reproducing a spatial sound

image, which is - dependent on the available data rate -
more or less similar to that of the original multi-channel
audio content.
However, given some pre-coded audio material (i.e. spatial
sound described by a given number of reproduction channel
signals), such a codec does not offer any means for a-
posteriori and interactive rendering of single audio
objects according to the liking of the listener. On the
other hand, there are spatial audio object coding
techniques which are specially designed for the latter
purpose, but since the parametric representations used in
such systems are different from those for multi-channel
audio signals, separate decoders are needed in case one
wants to benefit from both techniques in parallel. The
drawback that results from this situation is that, although
the back-ends of both systems fulfill the same task, which
is rendering of spatial audio scenes on a given loudspeaker
setup, they have to be implemented redundantly, i.e. two
separate decoders are necessary to provide both
functionalities.
Another limitation of the prior-art object coding
technology is the lack of a means for storing and / or
transmitting pre-rendered spatial audio object scenes in a
backwards compatible way. The feature of enabling
interactive positioning of single audio objects provided by
the spatial audio object coding paradigm turns out to be a
drawback when it comes to identical reproduction of a
readily rendered audio scene.
Summarizing, one is confronted with the unfortunate
situation that, although a multi-channel playback
environment may be present which implements one of the
above approaches, a further playback environment may be
required to also implement the second approach. It may be
noted, that according to the longer history, channel-based
coding schemes are much more common, such as, for example,

the famous 5.1 or 7.1/7.2 multi-channel signals stored on
DVD or the like.
That is, even if a multi-channel audio decoder and
associated playback equipment (amplifier stages and
loudspeakers) are present, a user needs an additional
complete set-up, i.e. at least an audio decoder, when he
wants to play back object-based coded audio data. Normally,
the multi-channel audio decoders are directly associated to
the amplifier stages and a user does not have direct access
to the amplifier stages used for driving the loudspeakers.
This is, for example, the case in most of the commonly
available multi-channel audio or multimedia receivers.
Based on existing consumer electronics, a user desiring to
be able to listen to audio content encoded with both
approaches would even need a complete second set of
amplifiers, which is, of course, an unsatisfying situation.
Summary of the Invention
It is therefore desirable to be able to provide a method to
reduce the complexity of systems, which are capable of both
decoding of parametric multi-channel audio streams as well
as parametrically coded spatial audio object streams.
An embodiment of the invention is a multi-channel parameter
transformer for generating a level parameter indicating an
energy relation between a first audio signal and a second
audio signal of a representation of a multi-channel spatial
audio signal, comprising: an object parameter provider for
providing object parameters for a plurality of audio
objects associated to a down-mix channel depending on the
object audio signals associated to the audio objects, the
object parameters comprising an energy parameter for each
audio object indicating an energy information of the object
audio signal; and a parameter generator for deriving the
level parameter by combining the energy parameters and

object rendering parameters related to a rendering
configuration.
According to a further embodiment of the present invention,
the parameter transformer generates a coherence parameter
and a level parameter, indicating a correlation or
coherence and an energy relation between a first and a
second audio signal of a multi-channel audio signal
associated to a multi-channel loudspeaker configuration.
The correlation- and level parameters are generated based
on provided object parameters for at least one audio object
associated to a down-mix channel, which is itself generated
using an object audio signal associated to the audio
object, wherein the object parameters comprise an energy
parameter indicating an energy of the object audio signal.
To derive the coherence and the level parameter, a
parameter generator is used, which combines the energy
parameter and additional object rendering parameters, which
are influenced by a playback configuration. According to
some embodiments, the object rendering parameters comprise
loudspeaker parameters indicating the location of the
playback loudspeakers with respect to a listening position.
According to some embodiments, the object rendering
parameters comprise object location parameters indicating
the location of the objects with respect to a listening
position. To this end, the parameter generator takes
advantage of synergy effects resulting from both spatial
audio coding paradigms.
According to a further embodiment of the present invention,
the multi-channel parameter transformer is operative to
derive MPEG Surround compliant coherence and level
parameters (ICC and CLD), which can furthermore be used to
steer an MPEG Surround decoder. It is noted that Inter-
channel coherence/cross-correlation (ICC) -represents the
coherence or cross-correlation between the two input
channels. When time differences are not included, coherence
and correlation are the same. Stated differently, both

terms point to the same characteristic, when inter channel
time differences or inter channel phase differences are not
used.
In this way, a multi-channel parameter transformer together
with a standard MPEG Surround-transformer can be used to
reproduce an object-based encoded audio signal. This has
the advantage, that only an additional parameter
transformer is required, which receives a spatial audio
object coded (SAOC) audio signal and which transforms the
object parameters such, that they can be used by a standard
MPEG SURROUND-decoder to reproduce the multi-channel audio
signal via the existing playback equipment. Therefore,
common playback equipment can be used without major
modifications to also reproduce spatial audio object coded
content.
According to a further embodiment of the present invention,
the generated coherence and level parameters are
multiplexed with the associated down-mix channel into a
MPEG SURROUND compliant bitstream. Such a bitstream can
then be fed to a standard MPEG SURROUND-decoder without
requiring any further modifications to the existing
playback environment.
According to a further embodiment of the present invention,
the generated coherence and level parameters are directly
transmitted to a slightly modified MPEG Surround-decoder,
such that the computational complexity of a multi-channel
parameter transformer can be kept low.
According to a further embodiment of the present invention,
the generated multi-channel parameters (coherence parameter
and level parameter) are stored after the generation, such
that a multi-channel parameter transformer can also be used
as a means for preserving the spatial information gained
during scene rendering. Such scene rendering can, for
example, also be performed at the music-studio while

generating the signals, such that a multi-channel
compatible signal can be generated without any additional
effort, using a multi-channel parameter transformer as
described in more detail in the following paragraphs. Thus,
pre-rendered scenes could be reproduced using legacy
equipment.
Brief Description of the Drawings
Prior to a more detailed description of several embodiments
of the present invention, a short review of the multi-channel
audio coding and object audio coding techniques and
spatial audio object coding techniques will be given. To
this end, reference will also be made to the enclosed
Figures.
Fig. la shows a prior art multi-channel audio coding
scheme;
Fig. lb shows a prior art object coding scheme;
Fig. 2 shows a spatial audio object coding scheme;
Fig. 3 shows an embodiment of a multi-channel parameter
transformer;
Fig. 4 shows an example for a multi-channel loudspeaker
configuration for playback of spatial audio
content; and
Fig. 5 shows an example for a possible multi-channel
parameter representation of spatial audio
content;
Figs. 6a and 6b show application scenarios for spatial
audio object coded content;

Fig. 7 shows an embodiment of a multi-channel parameter
transformer; and
Fig. 8 shows an example of a method for generating a
coherence parameter and a correlation parameter.
Detailed Description of Preferred Embodiments
Fig. la shows a schematic view of a multi-channel audio
encoding and decoding scheme, whereas Fig. lb shows a
schematic view of a conventional audio object coding
scheme. The multi-channel coding scheme uses a number of
provided audio channels, i.e. audio channels already mixed
to fit a predetermined number of loudspeakers. A multi-channel
encoder 4 (SAC) generates a down-mix signal 6,
being an audio signal generated using audio channels 2a to
2d. This down-mix signal 6 can, for example, be a
monophonic audio channel or two audio channels, i.e. a
stereo signal. To partly compensate for the loss of
information during the down-mix, the multi-channel encoder
4 extracts multi-channel parameters, which describe the
spatial interrelation of the signals of the audio channels
2a to 2d. This information is transmitted, together with
the down-mix signal 6, as so-called side information 8 to a
multi-channel decoder 10. The multi-channel decoder 10
utilizes the multi-channel parameters of the side
information 8 to create channels 12a to 12d with the aim of
reconstructing channels 2a to 2d as precisely as possible.
This can, for example, be achieved by transmitting level
parameters and correlation parameters, which describe an
energy relation between individual channel pairs of the
original audio channels 2a and 2d and which provide a
correlation measure between pairs of channels of the audio
channels 2a to 2d.
When decoding, this information can be used to redistribute
the audio channels comprised in the down-mix signal to the

reconstructed audio channels 12a to 12d. It may be noted,
that the generic multi-channel audio, scheme is implemented
to reproduce the same number of reconstructed channels 12a
to 12d as the number of original audio channels 2a to 2d
input into the multi-channel audio encoder 4. However,
other decoding schemes can also be implemented, reproducing
more or less channels than the number of the original audio
channels 2a to 2d.
In a way, the multi-channel audio techniques schematically
sketched in Fig. la (for example the recently standardized
MPEG spatial audio coding scheme, i.e. MPEG Surround) can
be understood as bitrate-efficient and compatible extension
of existing audio distribution infrastructure towards
multi-channel audio/surround sound.
Fig. lb details the prior art approach to object-based
audio coding. As an example, coding of sound objects and
the ability of "content-based interactivity" is part of the
MPEG-4 concept. The conventional audio object coding
technique schematically sketched in Fig. lb follows a
different approach, as it does not try to transmit a number
of already existing audio channels but to rather transmit a
complete audio scene having multiple audio objects 22a to
22d distributed in space. To this end, a conventional audio
object coder 20 is used to code multiple audio objects 22a
to 22d into elementary streams 24a to 24d, each audio
object having an associated elementary stream. The audio
objects 22a to 22d (sound sources) can, for example, be
represented by a monophonic audio channel and associated
energy parameters, indicating the relative level of the
audio object with respect to the remaining audio objects in
the scene. Of course, in a more sophisticated
implementation, the audio objects are not limited to be
represented by monophonic audio channels. Instead, for
example, stereo audio objects or multi-channel audio
objects may be encoded.

A conventional audio object decoder 28 aims at reproducing
the audio objects 22a to 22d, to derive reconstructed audio
objects 28a to 28d. A scene composer 30 within a
conventional audio object decoder allows for a discrete
positioning of the reconstructed audio objects 28a to 28d
(sources) and the adaptation to various loudspeakers set-
ups. A scene is fully defined by a scene description 34 and
associated audio objects. Some conventional scene composers
30 expect a scene description in a standardized language,
e.g. BIFS (binary format for scene description) . On the
decoder side, arbitrary loudspeaker set-ups may be present
and the decoder provides audio channels 32a to 32e to
individual loudspeakers, which are optimally tailored to
the reconstruction of the audio scene, as the full
information on the audio scene is available on the decoder
side. For example, binaural rendering is feasible, which
results in two audio channels generated to provide a
spatial impression when listened to via headphones.
An optional user interaction to the scene composer 30
enables a repositioning/repanning of the individual audio
objects on the reproduction side. Additionally, positions
or levels of specifically selected audio objects can be
modified, to, for example, increase the intelligibility of
a talker, when ambient noise objects or other audio objects
related to different talkers in a conference are
suppressed, i.e. decreased in level.
In other words, conventional audio object coders encode a
number of audio objects into elementary streams, each
stream associated to one single audio object. The
conventional decoder decodes these streams and composes an
audio scene under the control of a scene description (BIFS)
and optionally based on user interaction. In terms of
practical application, this approach suffers from several
disadvantages:

Due to the separate encoding of each individual audio
(sound) object, the required citrate for transmission of
the whole scene is significantly higher than rates used for
a monophonic/stereophonic transmission of compressed audio.
Obviously, the required bitrate grows approximately
proportionally with the number of transmitted audio
objects, i.e. with the complexity of the audio scene.
Consequently, due to the separate decoding of each sound
object, the computational complexity for the decoding
process significantly exceeds that one of a regular
mono/stereo audio decoder. The required computational
complexity for decoding grows approximately proportionally
with the number of transmitted objects as well(assuming a
low complexity composition procedure). When using advanced
composition capabilities, i.e. using different
computational nodes, these disadvantages are further
increased by the complexity associated with the
synchronization of corresponding audio nodes and with the
overall complexity in running a structured audio engine.
Furthermore, since the total system involves several audio
decoder components and a BIFS-based composition unit, the
complexity of the required structure is an obstacle to the
implementation in real-world applications. Advanced
composition capabilities furthermore require the
implementation of a structured audio engine with the above-
mentioned complications.
Fig. 2 shows an embodiment of the inventive spatial audio
object coding concept, allowing for a highly efficient
audio object coding, circumventing the previously mentioned
disadvantages of common implementations.
As it will become apparent from the discussion of Fig. 3
below, the concept may be implemented by modifying an
existing MPEG Surround structure. However, the use of the
MPEG Surround-framework is not mandatory, since other

common multi-channel encoding/decoding frameworks can also
be used to implement the inventive concept.
Utilizing existing multi-channel audio coding structures,
such as MPEG Surround, the inventive concept evolves into a
bitrate-efficient and compatible extension of existing
audio distribution infrastructure towards the capability of
using an object-based representation. To distinguish from
the prior approaches of audio object coding (AOC) and
spatial audio coding (multi-channel audio coding) ,
embodiments of the present invention will in the following
be referred to using the term spatial audio object coding
or its abbreviation SAOC.
The spatial audio object coding scheme shown in Fig. 2 uses
individual input audio objects 50a to 50d. Spatial audio
object encoder 52 derives one or more down-mix signals 54
(e.g. mono or stereo signals) together with side
information 55 having information of the properties of the
original audio scene.
The SAOC-decoder 56 receives the down-mix signal 54
together with the side information 55. Based on the down-
mix signal 54 and the side information 55, the spatial
audio object decoder 56 reconstructs a set of audio objects
58a to 58d. Reconstructed audio objects 58a to 58d are
input into a mixer/rendering stage 60, which mixes the
audio content of the individual audio objects 58a to 58d to
generate a desired number of output channels 62a and 62b,
which normally correspond to a multi-channel loudspeaker
set-up intended to be used for playback.
Optionally, the parameters of the mixer/renderer 60 can be
influenced according to a user interaction or control 64,
to allow interactive audio composition and thus maintain
the high flexibility of audio object coding.

The concept of spatial audio object coding shown in Fig. 2
has several great advantages as compared to other multi-channel
reconstruction scenarios.
The transmission is extremely bitrate-efficient due to the
use of down-mix signals and accompanying object parameters.
That is, object based side information is transmitted
together with a down-mix signal, which is composed of audio
signals associated to individual audio objects. Therefore,
the bit rate demand is significantly decreased as compared
to approaches, where the signal of each individual audio
object is separately encoded and transmitted. Furthermore,
the concept is backwards compatible to already existing
transmission structures. Legacy devices would simply render
(compose) the downmix signal.
The reconstructed audio objects 58a to 58d can be directly
transferred to a mixer/renderer 60 (scene composer). In
general, the reconstructed audio objects 58a to 58d could
be connected to any external mixing device (mixer/renderer
60), such that the inventive concept can be easily
implemented into already existing playback environments.
The individual audio objects 58a ... d could principally be
used as a solo presentation, i.e. be reproduced as a single
audio stream, although they are usually not intended to
serve as a high quality solo reproduction.
In contrast to separate SAOC decoding and subsequent
mixing, a combined SAOC-decoder and mixer/renderer is
extremely attractive because it leads to very low
implementation complexity. As compared to the straight
forward approach, a full decoding/reconstruction of the
objects 58a to 58d as an intermediate representation can be
avoided. The necessary computation is mainly related to the
number of intended output rendering channels 62a and 62b.
As it becomes apparent from Fig. 2, mixer/renderer 60
associated to the SAOC-decoder can in principle be any
algorithm suitable of combining single audio objects into a

scene, i.e. suitable of generating output audio channels
62a and 6b associated to individual loudspeakers of a
multi-channel loudspeaker set-up. This could, for example,
include mixers performing amplitude panning (or amplitude
and delay panning), vector based amplitude panning (VBAP
schemes) and binaural rendering, i.e. rendering intended to
provide a spatial listening experience utilizing only two
loudspeakers or headphones. For example, MPEG Surround
employs such binaural rendering approaches.
Generally, transmitting down-mix signals 54 associated with
corresponding audio object information 55 can be combined
with arbitrary multi-channel audio coding techniques, such
as, for example, parametric stereo, binaural cue coding or
MPEG Surround.
Fig. 3 shows an embodiment of the present invention, in
which object parameters are transmitted together with a
down-mix signal. In the SAOC decoder structure 120, a MPEG
Surround decoder can be used together with a multi-channel
parameter transformer, which generates MPEG parameters
using the received object parameters. This combination
results in an spatial audio object decoder 120 with
extremely low complexity. In other words, this particular
example offers a method for transforming (spatial audio)
object parameters and panning information associated with
each audio object into a standards compliant MPEG Surround
bitstream, thus extending the application of conventional
MPEG Surround decoders from reproducing multi-channel audio
content towards the interactive rendering of spatial audio
object coding scenes. This is achieved without having to
apply modifications to the MPEG Surround decoder itself.
The embodiment shown in Fig. 3 circumvents the drawbacks of
conventional technology by using a multi-channel parameter
transformer together with an MPEG Surround decoder. While
the MPEG Surround decoder is commonly available technology,
a multi-channel parameter transformer provides a

transcoding capability from SAOC to MPEG Surround. These
will be detailed in the following paragraphs, which will
additionally make reference to Figs. 4 and 5, illustrating
certain aspects of the combined technologies.
In Fig. 3, an SAOC decoder 120 has an MPEG Surround decoder
100 which receives a down-mix signal 102 having the audio
content. The downmix signal can be generated by an encoder-
side downmixer by combining (e.g. adding) the audio object
signals of each audio object in a sample by sample manner.
Alternatively, the combining operation can also take place
in a spectral domain or filterbank domain. The downmix
channel can be separate from the parameter bitstream 122 or
can be in the same bitstream as the parameter bitstream.
The MPEG Surround decoder 100 additionally receives spatial
cues 104 of an MPEG Surround bitstream, such as coherence
parameters ICC and level parameters CLD, both representing
the signal characteristics between two audio signals within
the MPEG Surround encoding/decoding scheme, which is shown
in Fig. 5 and which will be explained in more detail below.
A multi-channel parameter transformer 106 receives SAOC
parameters (object parameters) 122 related to audio
objects, which indicate properties of associated audio
objects contained within Downmix Signal 102. Furthermore,
the transformer 106 receives object rendering parameters
via an object rendering parameters input. These parameters
can be the parameters of a rendering matrix or can be
parameters useful for mapping audio objects into a
rendering scenario. Depending on the object positions
exemplarily adjusted by the user and input into block 12,
the rendering matrix will be calculated by block 112. The
output of block 112 is then input into block 106 and
particularly into the parameter generator 108 for
calculating the spatial audio parameters. When the
loudspeaker configuration changes, the rendering matrix or
generally at least some of the object rendering parameters

change as well. Thus, the rendering parameters depend on
the rendering configuration, which comprises the
loudspeaker configuration/playback configuration or the
transmitted or user-selected object positions, both of
which can be input into block 112.
A parameter generator 108 derives the MPEG Surround spatial
cues 104 based on the object parameters, which are provided
by object parameter provider (SAOC parser) 110. The
parameter generator 108 additionally makes use of rendering
parameters provided by a weighting factor generator 112.
Some or all of the rendering parameters are weighting
parameters describing the contribution of the audio objects
contained in the down-mix signal 102 to the channels
created by the spatial audio object decoder 120. The
weighting parameters could, for example, be organized in a
matrix, since these serve to map a number of N audio
objects to a number M of audio channels, which are
associated to individual loudspeakers of a multi-channel
loudspeaker set-up used for playback. There are two types
of input data to the multi-channel parameter transformer
(SAOC 2 MPS transcoder). The first input is an SAOC
bitstream 122 having object parameters associated to
individual audio objects, which indicate spatial properties
(e.g. energy information) of the audio objects associated
to the transmitted multi-object audio scene. The second
input is the rendering parameters (weighting parameters)
124 used for mapping the N objects to the M audio-channels.
As previously discussed, the SAOC bitstream 122 contains
parametric information about the audio objects that have
been mixed together to create the down-mix signal 102 input
into the MPEG Surround decoder 100. The object parameters
of the SAOC bitstream 122 are provided for at least one
audio object associated to the down-mix channel 102, which
was in turn generated using at least an object audio signal
associated to the audio object. A suitable parameter is,
for example, an energy parameter, indicating an energy of

the object audio signal, i.e. the strength of the
contribution of the object audio signal to the down-mix
102. In case a stereo downmix is used, a direction
parameter might be provided, indicating the location of the
audio object within the stereo downmix. However, other
object parameters are obviously also suited and could
therefore be used for the implementation.
The transmitted downmix does not necessarily have to be a
monophonic signal. It could, for example, also be a stereo
signal. In that case, 2 energy parameters might be
transmitted as object parameters, each parameter indicating
each object's contribution to one of the two channels of
the stereo signal. That is, for example, if 20 audio
objects are used for the generation of the stereo downmix
signal, 40 energy parameters would be transmitted as the
object parameters.
The SAOC bit stream 122 is fed into an SAOC parsing block,
i.e. into object parameter provider 110, which regains the
parametric information, the latter comprising, besides the
actual number of audio objects dealt with, mainly object
level envelope (OLE) parameters which describe the time-
variant spectral envelopes of each of the audio objects
present.
The SAOC parameters will typically be strongly time
dependent, as they transport the information, as to how the
multi-channel audio scene changes with time, for example
when certain objects emanate or others leave the scene. To
the contrary, the weighting parameters of rendering matrix
124 do often not have a strong time or frequency
dependency. Of course, if objects enter or leave the scene,
the number of required parameters changes abruptly, to
match the number of the audio objects of the scene.
Furthermore, in applications with interactive user control,
the matrix elements may be time variant, as they are then
deoendina on the actual input of a user.

In a further embodiment of the present invention,
parameters steering a variation of the weighting parameters
or the object rendering parameters or time-varying object
rendering parameters (weighting parameters) themselves may
be conveyed in the SAOC bitstream, to cause a variation of
rendering matrix 124. The weighting factors or the
rendering matri.x elements may be frequency dependent, if
frequency dependent rendering properties are desired (as
for example when a frequency-selective gain of a certain
object is desired).
In the embodiment of Fig. 3, the rendering matrix is
generated (calculated) by a weighting factor generator 112
(rendering matrix generation block) based on information
about the playback configuration (that is a scene
description). This might, on the one hand, be playback
configuration information, as for example loudspeaker
parameters indicating the location or the spatial
positioning of the individual loudspeakers of a number of
loudspeakers of the multi-channel loudspeaker configuration
used for playback. The rendering matrix is furthermore
calculated based on object rendering parameters, e.g. on
information indicating the location of the audio objects
and indicating an amplification or attenuation of the
signal of the audio object. The object rendering parameters
can, on the one hand, be provided within the SAOC bitstream
if a realistic reproduction of the multi-channel audio
scene is desired. The object rendering parameters (e.g.
location parameters and amplification information (panning
parameters)) can alternatively also be provided
interactively via a user interface. Naturally, a desired
rendering matrix, i.e. desired weighting parameters, can
also be transmitted together with the objects to start with
a naturally sounding reproduction of the audio scene as a
starting point for interactive rendering on the decoder
side.

The parameter generator (scene rendering engine) 108
receives both, the weighting factors and the object
parameters (for example the energy parameter OLE) to
calculate a mapping of the N audio objects to M output
channels, wherein M may be larger than, less than or equal
to N and furthermore even varying with time. When using a
standard MPEG Surround decoder 100, the resulting spatial
cues (for example, coherence and level parameters) may be
transmitted to the MPEG-decoder 100 by means of a
standards-compliant surround bitstream matching the down-
mix signal transmitted together with the SAOC bitstream.
Using a multi-channel parameter transformer 106, as
previously described, allows using a standard MPEG Surround
decoder to process the down-mix signal and the transformed
parameters provided by the parameter transformer 106 to
play back the reconstruction of the audio scene via the
given loudspeakers. This is achieved with the high
flexibility of the audio object coding-approach, i.e. by
allowing serious user interaction on the playback side.
As an alternative to the playback of a multi-channel
loudspeaker set-up, a binaural decoding mode of the MPEG
Surround decoder may be utilized to play back the signal
via headphones.
However, if minor modifications to the MPEG Surround
decoder 100 are acceptable, e.g. within a software-
implementation, the transmission of the spatial cues to the
MPEG Surround decoder could also be performed directly in
the parameter domain. I.e., the computational effort of
multiplexing the parameters into an MPEG Surround
compatible bitstream can be omitted. Apart from the
decrease in computational complexity, a further advantage
is to avoid of a quality degradation introduced by the
MPEG-conforming parameter quantization, since such
quantization of the generated spatial cues would in this
case no longer be necessary. As already mentioned, this

benefit calls for a more flexible MPEG Surround decoder
implementation, offering the possibility of a direct
parameter feed rather than a pure bitstream feed.
In another embodiment of the present invention, an MPEG
Surround compatible bitstream is created by multiplexing
the generated spatial cues and the down-mix signal, thus
offering the possibility of a playback via legacy
equipment. Multi-channel parameter transformer 106 could
thus also serve the purpose of transforming audio object
coded data into multi-channel coded data at the encoder
side. Further embodiments of the present invention, based
on the multi-channel parameter transformer of Fig. 3 will
in the following be described for specific object audio and
multi-channel implementations. Important aspects of those
implementations are illustrated in Figs. 4 and 5.
Fig. 4 illustrates an approach to implement amplitude
panning, based on one particular implementation, using
direction (location) parameters as object rendering
parameters and energy parameters as object parameters. The
object rendering parameters indicate the location of an
audio object. In the following paragraphs, angles αi 150
will be used as object rendering (location) parameters,
which describe the direction of origin of an audio object
152 with respect to a listening position 154. In the
following examples, a simplified two-dimensional case will
be assumed, such that one single parameter, i.e. an angle,
can be used to unambiguously parameterize the direction of
origin of the audio signal associated with the audio
object. However, it goes without saying, that the general
three-dimensional case can be implemented without having to
apply major changes. That is, having for exampled a three-
dimensional space, vectors could be used to indicate the
location of the audio objects within the spatial audio
scene. As an MPEG Surround decoder shall in the following
be used to implement the inventive concept, Fig. 4
additionally shows the loudspeaker locations of a five-

channel MPEG multi-channel loudspeaker configuration. When
the position of a centre loudspeaker 156a(C) is defined to
be at 0°, a right front speaker 156b is located at 30°, a
right surround speaker 156c is located at 110°, a left
surround speaker 156d is located at -110° and a left front
speaker 156e is located at -30°.
The following examples will furthermore be based on 5.1-
channel representations of multi-channel audio signals as
specified in the MPEG Surround standard, which defines two
possible parameterisations, that can be visualized by the
tree-structures shown in Fig. 5.
In case of the transmission of a mono-down-mix 160, the
MPEG Surround decoder employs a tree-structure
parameterization. The tree is populated by so-called OTT
elements (boxes) 162a to 162e for the first
parameterization and 164a to 164e for the second
parameterization.
Each OTT element up-mixes a mono-input into two output
audio signals. To perform the up-mix, each OTT element uses
an ICC parameter describing the desired cross-correlation
between the output signals and a CLD parameter describing
the relative level differences between the two output
signals of each OTT element.
Even though structurally similar, the two parameterizations
of Fig. 5 differ in the way the audio-channel content is
distributed from the monophonic down-mix 160. For example,
in the left tree-structure, the first OTT element 162a
generates a first output channel 166a and a second output
channel 166b. According to the visualization in Fig. 5, the
first output channel 166a comprises information on the
audio channels of the left front, the right front, the
centre and the low frequency enhancement channel. The
second output signal 166b comprises only information on the
surround channels, i.e. on the left surround and the right

surround channel. When compared to the second
implementation, the output of the first OTT element differs
significantly with respect to the audio channels comprised.
However, a multi-channel parameter transformer can be
implemented based on either of the two implementations.
Once the inventive concept is understood, it may also be
applied to other multi channel configurations than the ones
described below. For the sake of conciseness, the following
embodiments of the present invention focus on the left
parameterization of Fig. 5, without loss of generality. It
may furthermore be noted, that Fig. 5 only serves as an
appropriate visualization of the MPEG-audio concept and
that the computations are normally not performed in a
sequential manner, as one might be tempted to believe by
the visualizations of Fig. 5. Generally, the computations
can be performed in parallel, i.e. the output channels can
be derived in one single computational step.
In the embodiments briefly discussed in the following
paragraphs, an SAOC bitstream comprises (relative) levels
of each audio object in the down-mixed signal (for each
time-frequency tile separately, as is common practice
within a frequency-domain framework using, for example, a
filterbank or a time-to-frequency transformation).
Furthermore, the present invention is not limited to a
specific level representation of the objects, the
description below merely illustrates one method to
calculate the spatial cues for the MPEG Surround bitstream
based on an object power measure that can be derived from
the SAOC object parameterization.
As is apparent from Fig. 3, the rendering matrix W, which
is generated by weighting parameters and used by the
parameter generator 108 to map the objects Oi to the
required number of output channels (e.g. the number of
loudspeakers) s, has a number of weighting parameters,

which depends on the particular object index i and the
channel index s. As such, a weighting parameter ws,i denotes
the mixing gain of object i (1 ≤ i ≤ N) to loudspeaker s (1
≤ s ≤ M) . That is, W maps objects o = [o1 ... oN]T to
loudspeakers, generating the output signals for each
loudspeaker (here assuming a 5.1 set-up)
y=[ylf yrf yc yLFE yls yRs ]T, thus:
y = Wo .
The parameter generator (the rendering engine 108) utilizes
the rendering matrix W to estimate all CLD and ICC
parameters based on SAOC data σi2. With respect to the
visualizations of Fig. 5, it becomes apparent, that this
process has to be performed for each OTT element
independently. A detailed discussion will focus on the
first OTT element 162a, since the teachings of the
following paragraphs can be adapted to the remaining OTT
elements without further inventive skill.
As it can be observed, the first output signal 166a of OTT
element 162a is processed further by OTT elements 162b,
162c and 162d, finally resulting in output channels LF, RF,
C and LFE. The second output channel 166b is processed
further by OTT element 162e, resulting in output channels
LS and RS. Substituting the OTT elements of Fig. 5 with one
single rendering matrix W can be performed by using the
following matrix W:

The number N of the columns of matrix W is not fixed, as N
is the number of audio objects, which might be varying.

One possibility to derive the spatial cues (CLD and ICC)
for the OTT element 162a is that the respective
contribution of each object to the two outputs of OTT
element 0 is obtained by summation of the corresponding
elements in W. This summation gives a sub-rendering matrix
W0 of OTT element 0:

The problem is now simplified to estimating the level
difference and correlation for sub-rendering matrix W0 (and
for similarly defined sub-rendering matrices W1, W2, W3 and
W4 related to the OTT elements 1, 2, 3 and 4,
respectively).


virtual signals, since these signals represent a
combination of loudspeaker signals and do not constitute
actually occurring audio signals. At this point, it is
emphasized that the tree structures in Fig. 5 are not used
for generation of the signals. This means that in the MPEG
surround decoder, any signals between the one-to-two boxes
do not exist. Instead, there is a big upmix matrix using
the donwnmix and the different parameters to more or less
directly generate the loudspeaker signals.
Below, the grouping or identification of channels for the
left configuration of Fig. 5 is described.
For box 162a, the first virtual signal is the signal
representing a combination of the loudspeaker signals lf,
rf, c, lfe. The second virtual signal is the virtual signal
representing a combination of ls and rs.
For box 162b, the first audio signal is a virtual signal
and represents a group including a left front channel and a
right front channel, and the second audio signal is a
virtual signal and represents a group including a center
channel and an lfe channel.
For box 162e, the first audio signal is a loudspeaker
signal for the left surround channel and the second audio
signal is a loudspeaker signal for the right surround
channel.
For box 162c, the first audio signal is a loudspeaker
signal for the left front channel and the second audio
signal is a loudspeaker signal for the right front channel.
For box 162d, the first audio signal is a loudspeaker
signal for the center channel and the second audio signal

is a loudspeaker signal for the low frequency enhancement
channel.
In these boxes, the weighting parameters for the first
audio signal or the second audio signal are derived by
combining object rendering parameters associated to the
channels represented by the first audio signal or the
second audio signal as will be outlined later on.
Below, the grouping or identification of channels for the
right configuration of Fig. 5 is described.
For box 164a, the first audio signal is a virtual signal
and represents a group including a left front channel, a
left surround channel, a right front channel, and a right
surround channel, and the second audio signal is a virtual
signal and represents a group including a center channel
and a low frequency enhancement channel.
For box 164b, the first audio signal is a virtual signal
and represents a group including a left front channel and a
left surround channel, and the second audio signal is a
virtual signal and represents a group including a right
front channel and a right surround channel.
For box 164e, the first audio signal is a loudspeaker
signal for the center channel and the second audio signal
is a loudspeaker signal for the low frequency enhancement
channel.
For box 164c, the first audio signal is a loudspeaker
signal for the left front channel and the second audio
signal is a loudspeaker signal for the left surround
channel.

For box 164d, the first audio signal is a loudspeaker
signal for the right front channel and the second audio
signal is a loudspeaker signal for the right surround
channel.
In these boxes, the weighting parameters for the first
audio signal or the second audio signal are derived by
combining object rendering parameters associated to the
channels represented by the first audio signal or the
second audio signal as will be outlined later on.
The above mentioned virtual signals are virtual, since they
do not necessarily occur in an embodiment. These virtual
signals are used to illustrate the generation of power
values or the distribution of energy which is determined by
CLD for all boxes e.g. by using different sub-rendering
matrices W1. Again, the left side of Fig. 5 is described
first
Above, the sub-rendering matrix W0 for box 162a has been
shown.
For box 162b, the sub-rendering matrix is defined as:

Depending on the implementation, the respective CLD and ICC
parameter may be quantized and formatted to fit into an
MPEG Surround bitstream, which could be fed into MPEG
Surround decoder 100. Alternatively, the parameter values
could be passed to the MPEG Surround decoder on a parameter
level, i.e. without quantization and formatting into a
bitstream. To not only achieve repanning of the objects,
i.e. distributing these signal energies appropriately,
which can be achieved using the above approach utilizing
the MPEG-2 structure of Fig. 5, but to also implement
attenuation or amplification, so-called arbitrary down-mix
gains may also be generated for a modification of the down-
mix signal energy. Arbitrary down-mix gains (ADG) allow for
a spectral modification of the down-mix signal itself,
before it is processed by one of the OTT elements. That is,
arbitrary down-mix gains are per se frequency dependent.
For an efficient implementation, arbitrary down-mix gains
ADGs are represented with the same frequency resolution and
the same quantizer steps as CLD-parameters. The general
goal of the application of ADGs is to modify the
transmitted down-mix in a way that the energy distribution
in the down-mix input signal resembles the energy of the
down-mix of the rendered system output. Using the weighting
parameters Wk,i of the rendering matrix W and the
transmitted object powers σi2 appropriate ADGs can be
calculated using the following equation:

and it is assumed, that the power of the input down-mix
signal is equal to the sum of the object powers (i = object
index, k = channel index).

As previously discussed, the computation of the CLD and
ICC-parameters utilizes weighting parameters indicating a
portion of the energy of the object audio signal associated
to loudspeakers of the multi-channel loudspeaker
configuration. These weighting factors will generally be
dependent on scene data and playback configuration data,
i.e. on the relative location of audio objects and
loudspeakers of the multi-channel loudspeaker set-up. The
following paragraphs will provide one possibility to derive
the weighting parameters, based on the object audio
parameterization introduced in Fig. 4, using an azimuth
angle and a gain measure as object parameters associated to
each audio object.
As already outlined above, there are independent rendering
matrices for each time/frequency tile; however in the
following only one single time/frequency tile is regarded
for the sake of clarity. The rendering matrix W has got M
lines (one for each output channel) and, N columns (one for
each audio object) where the matrix element in line s and
column i represents the mixing weight with which the
particular audio object contributes to the respective
output channel:

The matrix elements are calculated from the following scene
description and loudspeaker configuration parameters:
Scene description (these parameters can vary over time):
• Number of audio objects: N ≥ 1
• Azimuth angle for each audio object: αi (1 ≤ i ≤ N)
• Gain value for each object: gi (1 ≤ i ≤ N)
Loudspeaker configuration (usually these parameters are
time-invariant):

• Number of output channels (= speakers): M ≥ 2
• Azimuth angle for each speaker: θS (1 ≤ s ≤ M)
• θs ≤ θs+i with 1 s ≤ M-l
The elements of the mixing matrix are derived from these
parameters by pursuing the following scheme for each audio
object i:
• Find index s' (1 ≤ s' ≤ M) with θS- ≤ αi ≤ θSS+1 (θM+1 : =
θ1+2Π)
• Apply amplitude panning (e.g. tangent law) between
speakers s' and s'+l (between speakers M and 1 in case
of s'=M). In the following description, the variables
v are the panning weights, i.e. the scaling factors to
be applied to a signal, when it is distributed between
two channels, as for example illustrated in Fig. 4.:

With respect to the above equations, it may be noted that
in the two-dimensional case, an object audio signal
associated to an audio object of the spatial audio scene
will be distributed between the two speakers of the multi-
channel loudspeaker configuration, which are closest to the
audio object. However, the object parameters chosen for the
above implementation are not the only object parameters
which can be used to implement further embodiments of the
present invention. For example, in' a three-dimensional
case, object parameters indicating the location of the
loudspeakers or the audio objects may be three-dimensional
vectors. Generally, two parameters are required for the
two-dimensional case and three parameters are required for
the three-dimensional case, when the location shall be
unambiguously defined. However, even in the two-dimensional
case, different parameterizations may be used, for example
transmitting two coordinates within a rectangular
coordinate system. It may furthermore be noted, that the
optional panning rule parameter p, which is within a range
of 1 to 2, is an arbitrary panning rule parameter, which is

set to reflect room acoustic properties of a reproduction
system/room, and which is, according to some embodiments of
the present invention, additionally applicable. Finally,
the weighting parameters WS,i can be derived according to
the following formula, after the panning weights V1,i and
V2,i have been derived according to the above equations. The
matrix elements are finally given by the following
equations:

The previously introduced gain factor gi, which is
optionally associated to each audio object, may be used to
emphasize or suppress individual objects. This may, for
example, be performed on the receiving side, i.e. in the
decoder, to improve the intelligibility of individually
chosen audio objects.
The following example of audio object 152 of Fig. 4 shall
again serve to clarify the application of the above
equations. The example utilizes the ITU-R BS.775-1
conforming 3/2-channel setup previously described. It is
the aim to derive the desired panning direction of an audio
object i, characterized by an azimuthal angle αi = 60°,
with an arbitrary panning gain gi of 1, (i.e. 0 dB) . With
this example, the playback room shall exhibit some
reverberation, parameterized by the panning rule parameter
p = 2. According to Fig. 4, it is apparent that the closest
loudspeakers are the right front loudspeaker 156b and the
right surround loudspeaker 156c. Therefore, the panning
weights can be found by solving the following equations:


After some mathematics, this leads to the solution:

Therefore, according to the above instructions, the
weighting parameters (matrix elements) associated to the
specific audio object located in direction αi are derived
to be:

The above paragraphs detail embodiments of the present
invention utilizing only audio objects, which can be
represented by a monophonic signal, i.e. point-like
sources. However, the flexible concept is not restricted to
the application with monophonic audio sources. To the
contrary, one or more objects, which are to be regarded as
spatially "diffuse" do also fit well into the inventive
concept. Multi-channel parameters have to be derived in an
appropriate manner, when non point-like sources or audio
objects are to be represented. An appropriate measure to
quantify an amount of diffuseness between one or more audio
objects, is an object-related cross-correlation parameter
ICC.
In the SAOC system discussed so far all audio objects were
supposed to be point sources, i.e. pair-wise uncorrelated
mono sound sources without any spatial extent. However
there are also application scenarios in which it is
desirable to allow audio objects that comprise more than
only one audio channel, exhibiting to a certain degree
pair-wise (de)correlation. The simplest and probably most
important case out of these is represented by stereo
objects, i.e. objects consisting of two more or less
correlated channels that belong together. As an example,
such an object could represent the spatial image produced
by a symphony orchestra.

In order to smoothly integrate stereo objects into a mono
audio object based system as it is described above, both
channels of a stereo object are treated as individual
objects. The interrelationship of both part objects is
reflected by an additional cross-correlation parameter
which is calculated based on the same time/frequency grid
as is applied for the derivation of the sub-band power
values σi2. In other words: A stereo object is defined by a
set of parameter triplets per
time/frequency tile, where denotes the pair-wise
correlation between the two realizations of one object.
These two realizations are denoted by individual objects i
and j. having a pair-wise correlation ICCi,j.
For the correct rendering of stereo objects an SAOC decoder
must provide means for establishing the correct correlation
between those playback channels that participate in the
rendering of the stereo object, such that the contribution
of that stereo object to the respective channels exhibits a
correlation as claimed by the corresponding
parameter. An SAOC to MPEG Surround transcoder which is
capable of handling stereo objects, in turn, must derive
ICC parameters for the OTT boxes that are involved in
reproducing the related playback signals, such that the
amount of decorrelation between the output channels of the
MPEG Surround decoder fulfills this condition.
In order to do so, compared to the example given in the
previous section of this document, the calculation of the
powers p0,i and p0,2 and the cross-power R0 have to be
changed. Assuming the indices of the two audio objects that
together build a stereo object to be i1 and i2 the formulas
change in the following manner:



It can be observed easily that in case of
i2 and otherwise, these equations are identical to
those given in the previous section.
Having the capability of using stereo objects has the
obvious advantage, that the reproduction quality of the
spatial audio scene can be significantly enhanced, when
audio sources other than point sources can be treated
appropriately. Furthermore, the generation of a spatial
audio scene may be performed more efficiently, when one has
the capability of using premixed stereo signals, which are
widely available for a great number of audio objects.
The following considerations will furthermore show that the
inventive concept allows for the integration of point-like
sources, which have an "inherent" diffuseness. Instead of
objects representing point sources, as in the previous
examples, one or more objects may also be regarded as
spatially 'diffuse'. The amount of diffuseness can be
characterized by an object-related cross-correlation
parameter For , the object i represents a
point source, while for ICCit =0, the object is maximally
diffuse. The object-dependent diffuseness can be integrated
in the equations given above by filling in the correct
values.
When stereo objects are utilized, the derivation of the
weighting factors of the matrix M has to be adapted.
However, the adaptation can be performed without inventive
skill, as for the handling of stereo objects, two azimuth
positions (representing the azimuth values of the left and

the right "edge" of the stereo object) are converted into
rendering matrix elements.
As already mentioned, regardless of the type of audio
objects used, the rendering Matrix elements are generally
defined individually for different time/frequency tiles and
do in general differ from each other. A variation over time
may, for example, reflect a user interaction, through which
the panning angles and gain values for every individual
object may be arbitrarily altered over time. A variation
over frequency allows for different features influencing
the spatial perception of the audio scene, as, for example,
equalization.
Implementing the inventive concept using a multi-channel
parameter transformer allows for a number of completely
new, previously not feasible, applications. As, in a
general sense, the functionality of SAOC can be
characterized as efficient coding and interactive rendering
of audio objects, numerous applications requiring
interactive audio can benefit from the inventive concept,
i.e. the implementation of an inventive multi-channel
parameter transformer or an inventive method for a multi-
channel parameter transformation.
As an example, completely new interactive teleconferencing
scenarios become feasible. Current telecommunication
infrastructures (telephone, teleconferencing etc.) are
monophonic. That is, classical object audio coding cannot
be applied, since this requires the transmission of one
elementary stream per audio object to be transmitted.
However, these conventional transmission channels can be
extended in their functionality by introducing SAOC with a
single down-mix channel. Telecommunication terminals
equipped with an SAOC extension, that is mainly with a
multi-channel parameter transformer or an inventive object
parameter transcoder, are able to pick up several sound
sources (objects)and mix them into a single monophonic

down-mix signal which is transmitted in a compatible way by
using the existing coders (for example speech coders). The
side information (spatial audio object parameters or object
parameters) may be conveyed in a hidden, backwards
compatible way. While such advanced terminals produce an
output object stream containing several audio objects, the
legacy terminals will reproduce the downmix signal.
Conversely, the output produced by legacy terminals (i.e. a
downmix signal only) will be considered by SAOC transcoders
as a single audio object.
The principle is illustrated in Fig. 6a. At a first
teleconferencing site 200, A objects (talkers) may be
present, whereas at a second teleconferencing site 202 B
objects (talkers) may be present. According to SAOC, object
parameters can be transmitted from the first
teleconferencing site 200 together with an associated down-
mix signal 204, whereas a down-mix signal 206 can be
transmitted from the second teleconferencing site 202 to
the first teleconferencing site 200, associated by audio
object parameters for each of the B objects at the second
teleconferencing site 202. This has the tremendous
advantage, that the output of multiple talkers can be
transmitted using only one single down-mix channel and that
furthermore, additional talkers may be emphasized at the
receiving site, as the additional audio object parameters,
associated to the individual talkers, are transmitted in
association with the down-mix signal.
This allows, for example, a user to emphasize one specific
talker of interest by applying object-related gain values
gi, thus making the remaining talkers nearly inaudible.
This would not be possible when using conventional multi-
channel audio techniques, since these would try to
reproduce the original spatial audio scene as naturally as
possible, without the possibility of allowing a user
interaction to emphasize selected audio objects.

Fig. 6b illustrates a more complex scenario, in which
teleconferencing is performed among three teleconferencing
sites 200, 202 and 208. Since each site is only capable of
receiving and sending one audio signal, the infrastructure
uses so-called multi-point control units MCU 210. Each site
200, 202 and 208 is connected to the MCU 210. From each
site to the MCU 210, a single upstream contains the signal
from the site. The downstream for each site is a mix of the
signals of all other sites, possibly excluding the site's
own signal (the so-called "N-l signal").
According to the previously discussed concept and the
inventive parameter transcoders, the SAOC bitstream format
supports the ability to combine two or more object streams,
i.e. two streams having a down-mix channel and associated
audio object parameters into a single stream in a
computationally efficient way, i.e. in a way not requiring
a preceding full reconstruction of the spatial audio scene
of the sending site. Such a combination is supported
without decoding/re-encoding of the objects according to
the present invention. Such a spatial audio object coding
scenario is particularly attractive when using low delay
MPEG communication coders, such as, for example low delay
AAC.
Another field of interest for the inventive concept is
interactive audio for gaming and the like. Due to its low
computational complexity and independency from a particular
rendering set-up, SAOC is ideally suited to represent sound
for interactive audio, such as gaming applications. The
audio could furthermore be rendered depending on the
capabilities of the output terminal. As an example, a
user/player could directly influence the rendering/mixing
of the current audio scene. Moving around in a virtual
scene is reflected by an adaptation of the rendering
parameters. Using a flexible set of SAOC
sequences/bitstreams would enable the reproduction of a
non-linear game story controlled by user interaction.

According to a further embodiment of the present invention,
inventive SAOC coding is applied within a multi-player
game, in which a user interacts with other players in the
same virtual world/scene. For each user, the video and
audio scene is based on his position and orientation in the
virtual world and rendered accordingly on his local
terminal. General game parameters and specific user data
(position, individual audio; chat etc.) is exchanged
between the different players using a common game server.
With legacy techniques, every individual audio source not
available by default on each client gaming device
(particularly user chat, special audio effects) in a game
scene has to be encoded and sent to each player of the game
scene as an individual audio stream. Using SAOC, the
relevant audio stream for each player can easily be
composed/combined on the game server, be transmitted as a
single audio stream to the player (containing all relevant
objects) and rendered at the correct spatial position for
each audio object (= other game players' audio).
According to a further embodiment of the present invention,
SAOC is used to play back object soundtracks with a control
similar to that of a multi-channel mixing desk using the
possibility to adjust relative level, spatial position and
audibility of instruments according to the listener's
liking. Such, a user can:
suppress/attenuate certain instruments for playing
along (Karaoke type of applications)
modify the original mix to reflect their preference
(e.g. more drums and less strings for a dance party or
less drums and more vocals for relaxation music)
choose between different vocal tracks (female lead
vocal via male lead vocal) according to their
preference.

As the above examples have shown, the application of the
inventive concept opens the field for a wide variety of
new, previously unfeasible applications. These applications
become possible, when using an inventive multi-channel
parameter transformer of Fig. 7 or when implementing a
method for generating a coherence parameter indicating a
correlation between a first and a second audio signal and a
level parameter, as shown in Fig. 8.
Fig. 7 shows a further embodiment of the present invention.
The multi-channel parameter transformer 300 comprises an
object parameter provider 302 for providing object
parameters for at least one audio object associated to a
down-mix channel generated using an object audio signal
which is associated to the audio object. The multi-channel
parameter transformer 300 furthermore comprises a parameter
generator 304 for deriving a coherence parameter and a
level parameter, the coherence parameter indicating a
correlation between a first and a second audio signal of a
representation of a multi-channel audio signal associated
to a multi-channel loudspeaker configuration and the level
parameter indicating an energy relation between the audio
signals. The multi-channel parameters are generated using
the object parameters and additional loudspeaker
parameters, indicating a location of loudspeakers of the
multi-channel loudspeaker configuration -to be used for
playback.
Fig. 8 shows an example of the implementation of an
inventive method for generating a coherence parameter
indicating a correlation between a first and a second audio
signal of a representation of a multi-channel audio signal
associated to a multi-channel loudspeaker configuration and
for generating a level parameter indicating an energy
relation between the audio signals. In a providing step
310, object parameters for at least one audio object
associated to a down-mix channel generated using an object

audio signal associated to the audio object, the object
parameters comprising a direction parameter indicating the
location of the audio object and an energy parameter
indicating an energy of the object audio signal are
provided.
In a transformation step 312, the coherence parameter and
the level parameter are derived combining the direction
parameter and the energy parameter with additional
loudspeaker parameters indicating a location of
loudspeakers of the multi-channel loudspeaker configuration
intended to be used for playback.
Further embodiments comprise an object parameter transcoder
for generating a coherence parameter indicating a
correlation between two audio signals of a representation
of a multi-channel audio signal associated to a multi-
channel loudspeaker configuration and for generating a
level parameter indicating an energy relation between the
two audio signals based on a spatial audio object coded bit
stream. This device includes a bit stream decomposer for
extracting a down-mix channel and associated object
parameters from the spatial audio object coded bit stream
and a multi-channel parameter transformer as described
before.
Alternatively or additionally, the object parameter
transcoder comprises a multi-channel bit stream generator
for combining the down-mix channel, the coherence parameter
and the level parameter to derive the multi-channel
representation of the multi-channel signal or an output
interface for directly outputting the level parameter and
the coherence parameter without any quantization and/or
entropy encoding.

Another object parameter transcoder has an output interface
is further operative to output the down mix channel in
association with the coherence parameter and the level
parameter or has a storage interface connected to the
output interface for storing the level parameter and the
coherence parameter on a storage medium.
Furthermore, the object parameter transcoder has a multi-
channel parameter transformer as described before, which is
operative to derive multiple coherence parameter and level
parameter pairs for different pairs of audio signals
representing different loudspeakers of the multi-channel
loudspeaker configuration.
Depending on certain implementation requirements of the
inventive methods, the inventive methods can be implemented
in hardware or in software. The implementation can be
performed using a digital storage medium, in particular a
disk, DVD or a CD having electronically readable control
signals stored thereon, which cooperate with a programmable
computer system such that the inventive methods are
performed. Generally, the present invention is, therefore,
a computer program product with a program code stored on a
machine readable carrier, the program code being operative
for performing the inventive methods when the computer
program product runs on a computer. In other words, the
inventive methods are, therefore, a computer program having
a program code for performing at least one of the inventive
methods when the computer program runs on a computer.
While the foregoing has been particularly shown and
described with reference to particular embodiments thereof,
it will be understood by those skilled in the art that
various other changes in the form and details may be made
without departing from the spirit and scope thereof. It is
to be understood that various changes may be made in

adapting to different embodiments without departing from
the broader concepts disclosed herein and comprehended by
the claims that follow.

What is claimed:
1. Multi-channel parameter transformer for generating a
level parameter indicating an energy relation between
a first audio signal and a second audio signal of a
representation of a multi-channel spatial audio
signal, comprising:
an object parameter provider for providing object
parameters for a plurality of audio objects
associated to a down-mix channel depending on the
object audio signals associated to the audio objects,
the object parameters comprising an energy parameter
for each audio object indicating an energy information
of the object audio signal; and
a parameter generator for deriving the level parameter
by combining the energy parameters and object
rendering parameters related to a rendering
configuration.
2. Multi-channel parameter transformer in accordance with
claim 1, which is adapted to additionally generate a
coherence parameter indicating a correlation between a
first and a second audio signal of a representation of
a multi-channel audio signal, and in which the
parameter generator is adapted to derive the coherence
parameter based on the object rendering parameters and
the energy parameter.
3. Multi-channel parameter transformer in accordance with
claim 1, in which the object rendering parameters
depend on object location parameters indicating a
location of the audio object.
4. Multi-channel parameter transformer in accordance with
claim 1, in which the rendering configuration
comprises a multi-channel loudspeaker configuration,

and in which the object rendering parameters depend on
loudspeaker parameters indicating locations of
loudspeakers of the multi-channel loudspeaker
configuration.
5. Multi-channel parameter transformer in accordance with
claim 1, in which the object parameter provider is
operative to provide object parameters additionally
comprising a direction parameter indicating a location
of the object with respect to a listening position;
and
in which the parameter generator is operative to use
object rendering parameters depending on loudspeaker
parameters indicating locations of loudspeakers with
respect to the listening position and on the direction
parameter.
6. Multi-channel parameter transformer in accordance with
claim 1, in which the object parameter provider is
operative to receive user input object parameters
additionally comprising a direction parameter
indicating a user-selected location of the object with
respect to a listening position within the loudspeaker
configuration; and
in which the parameter generator is operative to use
the object rendering parameters depending on
loudspeaker parameters indicating locations of
loudspeakers with respect to the listening position
and on the user input direction parameter.
7. Multi-channel parameter transformer in accordance with
claim 4, in which the object parameter provider and
the parameter generator are operative to use a
direction parameter indicating an angle within a
reference plane, the reference plane comprising the

listening position and also comprising the
loudspeakers having locations indicated by the
loudspeaker parameters.
8. Multi-channel parameter transformer in accordance with
claim 1, in which the parameter generator is adapted
to use first and second weighting parameters as object
rendering parameters, which indicate a portion of the
energy of the object audio signal to be distributed to
a first and a second loudspeaker of the multi-channel
loudspeaker configuration, the first and second
weighting parameters depending on loudspeaker
parameters indicating a location of loudspeakers of
the multi-channel loudspeaker configuration such that
the weighting parameters are unequal to zero when the
loudspeaker parameters indicate that the first and the
second loudspeakers are among the loudspeakers having
minimum distance with respect to a location of the
audio object.
9. Multi-channel parameter transformer in accordance with
claim 8, in which the parameter generator is adapted
to use weighting parameters indicating a greater
portion of the energy of the audio signal for the
first loudspeaker when the loudspeaker parameters
indicate a lower distance between the first
loudspeaker and the location of the audio object than
between the second loudspeaker and the location of the
audio object.
10. Multi-channel parameter transformer in accordance with
claim 8, in which the parameter generator comprises:
a weighting factor generator for providing the first
and the second weighting parameters wi and w2
depending on loudspeaker parameters Θ1 and Θ2 for the
first and second loudspeakers and on a direction

parameter a of the audio object, wherein the
loudspeaker parameters Θ1, Θ2 and the direction
parameter a indicate a direction of the location of
the loudspeakers and of the audio object with respect
to a listening position.
11. Multi-channel parameter transformer in accordance with
claim 10, in which the weighting factor generator is
operative to provide the weighting parameters w, and
w2 such that the following equations are satisfied:

p is an optional panning rule parameter which is set
to reflect room acoustic properties of a reproduction
system/room, and is defined as \