An Apparatus and a Method for Converting a First Parametric Spatial Audio Signal
into a Second Parametric Spatial Audio Signal
Description
The present invention relates to the field of audio processing, especially to the field of
parametric spatial audio processing and for converting a first parametric spatial audio
signal into a second parametric spatial audio signal.
Background of the Invention
Spatial sound recording aims at capturing a sound field with multiple microphones such
that at the reproduction side, a listener perceives the sound image, as it was present at the
recording location. Standard approaches for spatial sound recording use simple stereo
microphones or more sophisticated combinations of directional microphones, e.g., such as
the B-format microphones used in Ambisonics and described by M.A. Gerzon, "Periphony:
Width-Height Sound Reproduction," J. Aud. Eng. Soc, Vol. 21, No. 1, pp 2-10, 1973, in
the following referred to as [Ambisonics]. Commonly, these methods are referred to as
coincident-microphone techniques.
Alternatively, methods based on a parametric representation of sound fields can be applied,
which are referred to as parametric spatial audio coders. These methods determine a
downmix audio signal together with corresponding spatial side information, which are
relevant for the perception of spatial sound. Examples are Directional Audio Coding
(DirAC), as discussed in Pulkki, V., "Directional audio coding in spatial sound
reproduction and stereo upmixing," in Proceedings of The AES 28th International
Conference, pp. 251-258, Piteå, Sweden, June 30 - July 2, 2006, in the following referred
to as [DirAC], or the so-called spatial audio microphones (SAM) approach proposed in
Faller, C, "Microphone Front-Ends for Spatial Audio Coders", in Proceedings of the AES
125th International Convention, San Francisco, Oct. 2008, in the following referred to as
[SAM]. The spatial cue information basically consists of the direction-of-arrival (DOA) of
sound and the diffuseness of the sound field in frequency subbands. In a synthesis stage,
the desired loudspeaker signals for reproduction are determined based on the downmix
signal and the parametric side information.
In other words, the downmix signals and the corresponding spatial side information
represent the audio scene according to the set-up, e.g. the orientation and/or position of the
microphones, in relation to the different audio sources used at the time the audio scene was
recorded.
It is the object of the present invention to provide a concept for a flexible adaptation of the
recorded audio scene.
Summary of the Invention
This object is solved by an apparatus according to claim 1, a method according to claim 17
and a computer program according to claim 18.
All the aforementioned methods mentioned above have in common that they aim at
rendering the sound field at a reproduction side, as it was perceived at the recording
position. The recording position, i.e. the position of the microphones, can also be referred
to as the reference listening position. A modification of the recorded audio scene is not
envisaged in these known spatial sound-capturing methods.
On the other hand, modification of the visual image is commonly applied, for example, in
the context of video capturing. For example, an optical zoom is used in video cameras to
change the virtual position of the camera, giving the impression, the image was taken from
a different point of view. This is described by a translation of the camera position. Another
simple picture modification is the horizontal or vertical rotation of the camera around its
own axis. The vertical rotation is also referred to as panning or tilting.
Embodiments of the present invention provide an apparatus and a method, which also
allow virtually changing the listening position and/or orientation according to the visual
movement. In other words, the invention allows altering the acoustic image a listener
perceives during reproduction such that it corresponds to the recording obtained using a
microphone configuration placed at a virtual position and/or orientation other than the
actual physical position of the microphones. By doing so, the recorded acoustic image can
be aligned with the corresponding modified video image. For example, the effect of a
video zoom to a certain area of an image can be applied to the recorded spatial audio image
in a consistent way. According to the invention, this is achieved by appropriately
modifying the spatial cue parameters and/or the downmix signal in the parametric domain
of the spatial audio coder.
Embodiments of the present invention allow to flexibly change the position and/or
orientation of a listener within a given spatial audio scene without having to record the
spatial audio scene with a different microphone setting, for example, a different position
and/or orientation of the recording microphone set-up with regard to the audio signal
sources. In other words, embodiments of the present invention allow defining a virtual
listening position and/or virtual listening orientation that is different to the recording
position or listening position at the time the spatial audio scene was recorded.
Certain embodiments of the present invention only use one or several downmix signals
and/or the spatial side information, for example, the direction-of-arrival and the diffuseness
to adapt the downmix signals and/or spatial side information to reflect the changed
listening position and/or orientation. In other words, these embodiments do not require any
further set-up information, for example, geometric information of the different audio
sources with regard to the original recording position.
Embodiments of the present invention further receive parametric spatial audio signals
according to a certain spatial audio format, for example, mono or stereo downmix signals
with direction-of-arrival and diffuseness as spatial side information and convert this data
according to control signals, for example, zoom or rotation control signals and output the
modified or converted data in the same spatial audio format, i.e. as mono or stereo
downmix signal with the associated direction-of-arrival and diffuseness parameters.
In a particular embodiment, embodiments of the present invention are coupled to a video
camera or other video sources and modify the received or original spatial audio data into
the modified spatial audio data according to the zoom control or rotation control signals
provided by the video camera to synchronize, for example, the audio experience to the
video experience and, for example, to perform an acoustical zoom in case a video zoom is
performed and/or perform an audio rotation within the audio scene in case the video
camera is rotated and the microphones do not physically rotate with the camera because
they are not mounted on the camera.
Short Description of the Fies.
Embodiments of the present invention will be described in detail using the following Figs.
Fig. 1 shows a block diagram of a parametric spatial audio coder;
Fig. 2 shows the spatial audio coder of Fig. 1 together with an embodiment of the
spatial parameter modification block coupled between the spatial audio
analysis unit and the spatial audio synthesis unit of the spatial audio coder;
Fig. 3A corresponds to Fig. 2 and shows a more detailed embodiment of the spatial
parameter modification block;
Fig. 3B corresponds to Fig. 2 and shows a further more detailed embodiment of the
spatial parameter modification block;
Fig. 4 shows an exemplary geometric overview of an acoustical zoom;
Fig. 5A shows an example of a directional mapping function fp(k,n,f,d) for the
direction-of-arrival (DOA) mapping;
Fig. 5B shows an example of a diffuseness mapping function fd(k,n,f,d) for the
diffuseness mapping;
Fig. 6 shows different gain windows for the weighting filter H1(k,n,f,d) of the
direct sound component depending on a zoom factor; and
Fig. 7 shows an exemplary subcardioid window for the weighting filter H2(k,n,f,d)
for the diffuse component.
Equal or equivalent elements or elements with equal or equivalent functionality are
denoted in the following description of the Figs. by equal or equivalent reference numerals.
Detailed Description of the Invention
For a better understanding of embodiments of the present invention, a typical spatial audio
coder is described. The task of a typical parametric spatial audio coder is to reproduce the
spatial impression that was present at the point where it was recorded. Therefore, a spatial
audio coder consists of an analysis part 100 and a synthesis part 200, as shown in Fig. 1. At
the acoustic front end, N microphones 102 are arranged to obtain N microphone input
signals that are processed by the spatial audio analysis unit 100 to produce L downmix
signals 112 with L = N together with spatial side information 114. In the decoder, i.e. in the
spatial audio synthesis unit, the downmix signal 112 and the spatial side information 114
are used to compute M loudspeaker channels for M loudspeakers 202, which reproduce the
recorded sound field with the original spatial impression. The thick lines (the lines between
the microphones 102 and the spatial audio analysis unit 100, the L downmix signals 112
and the M signal lines between the spatial audio synthesis unit 200 and the M loudspeakers
202) symbolize audio data, whereas the thin lines 114 between the spatial audio analysis
unit 100 and the spatial audio synthesis unit 200 represent the spatial side information.
In the following, the basic steps included in the computation of the spatial parameters or, in
other words, for the spatial audio analysis as performed by the spatial audio analysis unit
100, will be described in more detail. The microphone signals are processed in a suitable
time/frequency representation, e.g., by applying a short-time Fourier Transform (STFT) or
any other filterbank. The spatial side information determined in the analysis stage contains
a measure corresponding to the direction-of-arrival (DOA) of sound and a measure of the
diffuseness of the sound field, which describes the relation between direct and diffuse
sound of the analyzed sound field.
In DirAC, it has been proposed to determine the DOA of sound as the opposite direction of
the active intensity vector. The relevant acoustic information is derived from a so-called B-
format microphone input, corresponding to the sound pressure and the velocity obtained by
microphones configuration providing a dipole pick-up pattern, which are aligned with the
axes of Cartesian coordinate system. In other words, the B-format consists of four signals,
namely w(t), x(t), y(t) and z(t). The first corresponds to the pressure measured by an
omnidirectional microphone, whereas the latter three are signals of microphones having
figure-of-eight pick-up patterns directed towards the three axes of a Cartesian coordinate
system. The signals x(t), y(t) and z(t) are proportional to the components of particle
velocity vectors directed towards x, y and z, respectively. Alternatively, the approach
presented in SAM uses a priori knowledge of the directivity pattern of stereo microphones
to determine the DOA of sound.
The diffuseness measure can be obtained by relating the active sound intensity to the
overall energy of the sound field as proposed in DirAC. Alternatively, the method as
described in SAM proposes to evaluate the coherence between different microphone
signals. It should be noted that diffuseness could also be considered as a general reliability
measure for the estimated DOA. Without loss of generality, in the following it is assumed
that the diffuseness lies in the range of [1, 0], where a value of 1 indicates a purely diffuse
sound field, and a value of 0 corresponds to the case where only direct sound is present. In
other embodiments, other ranges and values for the diffuseness can be used.
The downmix signal 112, which is accompanied with the side information 114, is
computed from the microphone input signals. It can be mono or include multiple audio
channels. In case of DirAC, commonly only a mono signal, corresponding to the sound
pressure, as obtained by an omnidirectional microphone is considered. For the SAM
approach, a two-channel stereo signal is used as downmix signal.
In the following, the synthesis of loudspeaker signals used for reproduction as performed
by the spatial audio synthesis unit 200 is described in further detail. The input of the
synthesis 200 is the downmix signal 112 and the spatial parameters 114 in their time-
frequency representation. From this data, M loudspeaker channels are calculated such that
the spatial audio image or spatial audio impression is reproduced correctly. Let Y1 (k,n),
with i = 1... M, denote the signal of the i-th physical loudspeaker channel in
time/frequency representation with the time and frequency indices k and n, respectively.
The underlying signal model for the synthesis is given by

where S(k,n) corresponds to direct sound component and N(k,n) represents the diffuse
sound component. Note that for correct reproduction of diffuse sound, a decorrelation
operation Di{ } is applied to the diffuse component of each loudspeaker channel. The
scaling factor gi(k,n) depends on the DOA of the direct sound included in the side
information and the loudspeaker configuration used for playback. A suitable choice is
given by the vector base amplitude panning approach proposed by Pulkki, V., "Virtual
sound source positioning using vector base amplitude panning," J. Audio Eng. Soc, Vol.
45, pp 456-466, June 1997, in the following referred to as [VBAP].
In DirAC, the direct sound component is determined by appropriate scaling of the mono
downmix signal W(k,n), and obtained according to:

The diffuse sound component is obtained according to

where M is the number of loudspeakers used.
In SAM, the same signal model as in (1) is applied, however, the direct and diffuse sound
components are computed based on the stereo downmix signals instead.
Fig. 2 shows a block diagram of an embodiment of the present invention integrated in the
exemplary environment of Fig. 1, i.e. integrated between a spatial analysis unit 100 and a
spatial audio synthesis unit 200. As explained based on Fig. 1, the original audio scene is
recorded with a specific recording set-up of microphones specifying the location and
orientation (in case of directional microphones) relative to the different audio sound
sources. The N microphones provide N physical microphone signals or channel signals,
which are processed by the spatial audio analysis unit 100 to generate one or several
downmix signals W 112 and the spatial side information 114, for example, the direction-
of-arrival (DOA) f 114a and the diffuseness ? 114b. In contrast to Fig. 1, these spatial
audio signals 112, 114a, 114b are not provided directly to the spatial audio synthesis unit
200, but are modified by an apparatus for converting or modifying a first parametric spatial
audio signal 112, 114a, 114b representing a first listening position and/or a first listening
orientation (in this example, the recording position and recording orientation) in a spatial
audio scene to a second parametric spatial audio signal 212, 214a, 214b, i.e. a modified
downmix signal Wmod 212, a modified direction-of-arrival signal fmod 214a and/or a
modified diffuseness signal ?mod 214b representing a second listening position and/or
second listening orientation that is different to the first listening position and/or first
listening orientation. The modified direction-of-arrival 214a and the modified diffuseness
214b are also referred to as modified spatial audio information 214. The apparatus 300 is
also referred to as a spatial audio signal modification unit or spatial audio signal
modification block 300. The apparatus 300 in Fig. 3A is adapted to modify the first
parametric spatial audio signal 112, 114 depending on a control signal d 402 provided by a,
e.g. external, control unit 400. The control signal 402 can, e.g. be a zoom control signal
defining or being a zoom factor d or a zoom parameter d, or a rotation control signal 402
provided by a zoom control and/or a rotational control unit 400 of a video camera. It
should be noted that a zoom in a certain direction and a translation in the same direction
are just two different ways of describing a virtual movement in that certain direction (the
zoom by a zoom factor, the translation by an absolute distance or by a relative distance
relative to a reference distance). Therefore, explanations herein with regard to a zoom
control signal apply correspondingly to translation control signals and vice versa, and the
zoom control signal 402 also refers to a translation control signal. The term d can on one
hand represent the control signal 402 itself, and on the other hand the control information
or parameter contained in the control signal. In further embodiments, the control parameter
d represents already the control signal 402. The control parameter or control information d
can be a distance, a zoom factor and/or a rotation angle and/or a rotation direction.
As can be seen from Fig. 2, the apparatus 300 is adapted to provide parametric spatial
audio signals 212, 214 (downmix signals and the associated side information/parameters)
in the same format as the parametric spatial audio signals 112, 114 it received. Therefore,
the spatial audio synthesis unit 200 is capable (without modifications) of processing the
modified spatial audio signal 212, 214 in the same manner as the original or recorded
spatial audio signal 112, 114 and to convert them to M physical loudspeaker signals 204 to
generate the sound experience to the modified spatial audio scene or, in other words, to the
modified listening position and/or modified listening orientation within the otherwise
unchanged spatial audio scene.
In other words, a block schematic diagram of an embodiment of the novel apparatus or
method is illustrated in Fig. 2. As can be seen, the output 112, 114 of the spatial audio
coder 100 is modified based on the external control information 402 in order to obtain a
spatial audio representation 212, 214 corresponding to a listening position, which is
different to the one used in the original location used for the sound capturing. More
precisely, both the downmix signals 112 and the spatial side information 114 are changed
appropriately. The modification strategy is determined by an external control 400, which
can be acquired directly from a camera 400 or from any other user interface 400 that
provides information about the actual position of the camera or zoom. In this embodiment,
the task of the algorithm, respectively, the modification unit 300 is to change the spatial
impression of the sound scene in the same way as the optical zoom or camera rotation
changes the point-of-view of the spectator. In other words, the modification unit 300 is
adapted to provide a corresponding acoustical zoom or audio rotation experience
corresponding to the video zoom or video rotation.
Fig. 3A shows a block diagram or system overview of an embodiment of the apparatus 300
that is referred to as "acoustical zoom unit". The embodiment of the apparatus 300 in Fig.
3A comprises a parameter modification unit 301 and a downmix modification unit 302.
The parameter modification unit 301 further comprises a direction-of-arrival modification
unit 301a and a diffuseness modification unit 301b. The parameter modification unit 301 is
adapted to receive the direction-of-arrival parameter 114a and to modify the first or
received direction-of-arrival parameter 114a depending on the control signal d 402 to
obtain the modified or second direction-of-arrival parameter 214a. The parameter
modification unit 301 is further adapted to ireceive the first or original diffuseness
parameter 114b and to modify the diffuseness parameter 114b by the diffuseness
modification unit 301b to obtain the second or modified diffuseness parameter 214b
depending on the control signal 402. The downmix modification unit 302 is adapted to
receive the one or more downmix signals 112 and to modify the first or original downmix
signal 112 to obtain the second or modified downmix signal 212 depending on the first or
original direction-of-arrival parameter 114a, the first or original diffuseness parameter
114b and/or the control signal 402.
If the camera is controlled independently from the microphones 102, embodiments of the
invention provide a possibility to synchronize the change of the audio scene or audio
perception according to the camera controls 402. In addition, the directions can be shifted
without modifying the downmix signals 112 if the camera 400 is only rotated horizontally
without the zooming, i.e. applying only a rotation control signal and no zooming control
signal 402. This is described by the "rotation controller" in Figs. 2 and 3.
The rotation modification is described in more detail in the section about directional
remapping or remapping of directions. The sections about diffuseness and downmix
modification are related to the translation or zooming application.
Embodiments of the invention can be adapted to perform both, a rotation modification and
a translation or zoom modification, e.g. by first performing the rotation modification and
afterwards the translation or zoom modification or vice versa, or both at the same time by
providing corresponding directional mapping functions.
To achieve the acoustical zooming effect, the listening position is virtually changed, which
is done by appropriately remapping the analyzed directions. To get a correct overall
impression of the modified sound scene, the downmix signal is processed by a filter, which
depends on the remapped directions. This filter changes the gains, as, e.g., sounds that are
now closer are increased in level, while sounds from regions out-of-interest may be
attenuated. Also, the diffuseness is scaled with the same assumptions, as, e.g., sounds that
appear closer to the new listening position have to be reproduced less diffuse than before.
In the following, a more detailed description of the algorithm or method performed by the
apparatus 300 is given. An overview of the acoustical zoom unit is given in Fig. 3A. First,
the remapping of the directions is described (block 301a, fp(k,n,f,d)), then the filter for the
diffuseness modification (block 301b, fd(k,n,f,d)) is illustrated. Block 302 describes the
downmix modification, which is dependent on the zoom control and the original spatial
parameters.
In the following section, the remapping of the directions, respectively the remapping of the
direction-of-arrival parameters as, for example, performed by direction modification block
301a, is described.
The direction-of-arrival parameter (DOA parameter) can be represented, for example, by a
unit vector e. For or a three-dimensional (3D) sound field analysis, the vector can be
expressed by

where the azimuth angle f corresponds to the DOA in the two-dimensional (2D) plane,
namely the horizontal plane. The elevation angle is given by ?. This vector will be altered,
according to the new virtual position of the microphone as described next.
Without loss of generality, an example of the DOA remapping is given for the two-
dimensional case for presentation simplicity (Fig. 4). A corresponding remapping of the
three-dimensional DOA can be done with similar considerations.
Fig. 4 shows a geometric overview of an exemplarily geometric overview of the acoustical
zoom. The position S marks the original microphone recording position, i.e., the original
listening position. A and B mark spatial positions within the observed 2-dimensional plane.
It is now assumed that the listening position is moved from S to S2, e.g. in direction of the
first listening orientation. As can be seen from Fig. 4, the sound emerging from spatial
position A stays in the same angular position relative to the recording location, whereas
sounds from the area or spatial position B are moved to the side. This is denoted by a
changing of the analyzed angle a to ß, ß thus denotes the direction-of-arrival of sound
coming from the angular position of B if the listener had been placed in S2. For the
considered example, the azimuth angle is increased from a to p as shown in Fig. 4. This
remapping of the direction-of-arrival information can be written as a vector transformation
according to

where f( ) denotes a remapping function and emod is the modified direction vector. This
function is a nonlinear transformation, dependent on the zoom factor d and the original
estimated DOAs. Fig. 5A shows examples for the mapping f( ) for different values of a as
can be applied in the two-dimensional example shown in Fig. 4, For the zoom control
factor of d - 1, i.e., no zoom is applied, the angles are equal to the original DOA a. For
increasing zoom control factors, the value of ß is increased, too. The function can be
derived from geometric considerations or, alternatively, be chosen heuristically. Thus,
remapping of the directions means that each DOA is modified according to the function
f( ). The mapping fp(k,n,f,d) is performed for every time and frequency bin (k,n).
Although, in Fig. 4 the zoom parameter d is depicted as a translational distance d between
the original listening position S and the modified listening position S2, as mentioned
before, d can also be a factor, e.g. an optical zoom like an 4x or 8x zoom. Especially for
the width or filter control, seeing d as a factor, not as a distance, allows for an easy
implementation of the acoustical zoom. In other words, the zoom parameter d is in this
case a real distance, or at least proportional to a distance.
It should be further noted that embodiments of the invention can also be adapted to support
besides the "zoom-in" as described above, e.g. reducing a distance to an object (e.g. to
object A in Fig. 4 by moving from position S to position S2), also a "zoom-out", e.g.
increasing a distance to an object (e.g. to object A in Fig. 4 by moving from position S2 to
position S). In this case the inverse considerations apply compared to the zoom-in as
described because objects positioned on a side of the listener (e.g. object B with regard to
position S2) move to the front of the listener when he moves to position S. In other words
the magnitudes of the angles are reduced (e.g. from ß to a).
The remapping of the directions or vector transformation is performed by the direction-of-
arrival modification unit 301a. Fig. 5A shows an exemplarily mapping function (dependent
on the zoom factor d) for the direction-of-arrivals for the scenario shown in Fig. 4. The
diagram of Fig. 5A shows the zoom factor on the x-axis ranging from 1 to 2 and the
modified or mapped angle ß on the y-axis. For a zoom factor of 1, ß = a, i.e. the initial
angle is not modified. Reference sign 512 refers to the mapping function fp for a = 10°,
reference sign 514 represents the mapping function fp for a = 30°, reference sign 516 the
mapping function fp(k,n,f,d) for a = 50°, reference sign 518 the mapping function
fp(k,n,f,d) for a = 70°, and reference sign 520 the mapping function fp(k,n,f,d) for a = 90°.
Embodiments of the invention can be adapted to use the same mapping function fp for all
time and frequency bin values defined by k and n, or, may use different mapping functions
for different time values and/or frequency bins.
As becomes apparent from the above explanations, the idea behind the filter fd is to change
the diffuseness ? such that it lowers the diffuseness for zoomed-in directions (f < |?|) and
increases the diffuseness for out-of-focus directions (f > |?|).
To simplify the determination of the mapped angle ß, certain embodiments of the
modification unit 301a are adapted to only use the direction and to assume that all sources,
e.g. A and B, defining the direction-of-arrival of the sound have the same distance to the
first listening position, e.g. are arranged on a unit radius.
If a loudspeaker setup is considered, which only reproduces sound coming from frontal
directions, e.g., a typical stereo loudspeaker setup, the mapping function f( ) can be
designed such that the maximum angle, to where DOAs are remapped, is limited. For
example, a maximum angle of ±60° is chosen, when the loudspeakers are positioned at
±60°. This way, the whole sound scene will stay in the front and is only widened, when the
zoom is applied.
In case of a rotation of the camera, the original azimuth values are just shifted such that the
new looking direction corresponds to an angle of zero. Thus, a horizontal rotation of the
camera by 20° would result in ß =a - 20°. Also, the downmix and the diffuseness are not
changed for this special case, unless a rotation and translation are carried out
simultaneously.
As can be seen from the aforementioned explanations, the rotational change or difference
is derived starting from the first listening orientation respectively first viewing orientation
(e.g. direction of the "nose" of the listener respectively viewer) defining a first reference or
0° orientation. When the listening orientation changes, the reference or 0° orientation
changes accordingly. Therefore, embodiments of the present invention change the original
angles or directions of arrival of the sound, i.e. the first directional parameter, according to
the new reference or 0° orientation such that the second directional parameter represents
the same "direction of arrival" in the audio scene, however relative to the new reference
orientation or coordinate system. Similar considerations apply to the translation
respectively zoom, where the perceived directions-of-arrival change due to the translation
or zoom in direction of the first listening orientation (see Fig. 4).
The first directional parameter 114a and the second directional parameter 214a can be two-
dimensional or three-dimensional vectors. In addition, the first directional parameter 114a
can be a vector, wherein the control signal 402 is a rotation control signal defining a
rotation angle (e.g. 20° in the aforementioned example) and a rotation direction (to the
right in the aforementioned two-dimensional example), and wherein the parameter
modification unit 301, 301a is adapted to rotate the vector by the rotation angle in a reverse
direction to the rotation direction (ß=a-20° in the aforementioned example) to obtain the
second directional parameter, i.e. the second or modified vector 214a.
In the following section, the diffuseness scaling as, for example, performed by the
diffuseness modification unit 301b is described in more detail.
The diffuseness is scaled with a DOA-dependent window. In certain embodiments, values
of the diffuseness ?(k,n) are decreased for the zoomed-in directions, while the diffuseness
values for the directions out-of-interest are increased. This corresponds to the observation
that sound sources are perceived less diffuse if they are located closer to the listening
position. Therefore, for example, for a minimum zoom factor (e.g. d = 1), the diffuseness is
not modified. The range of the visual angle covered by the camera image can be taken as a
controller for the scaling by which the diffuseness value is increased or decreased.
The terms zoomed-in-directions or directions-of-interest refer to an angular window of
interest, also referred to as central range of angles, that is arranged around the first or
original listening direction, e.g. the original 0° reference direction. The angular window or
central range is determined by the angular values y defining the border of the angular
window. The angular window and the width of the angular window can be defined by the
negative border angle -y and the positive border angle y, wherein the magnitude of the
negative border angle may be different to the positive border angle. In preferred
embodiments, the negative border angle and the positive border angle have the same
magnitude (symmetric window or central range of angles centered around the first listening
orientation). The magnitude of the border angle is also referred to as angular width and the
width of the window (from the negative border angle to the positive border angle) is also
referred to as total angular width.
According to embodiments of the invention, direction-of-arrival parameters, diffuseness
parameters, and/or direct or diffuse components can be modified differently depending on
whether the original direction-of-arrival parameter is inside the window of interest, e.g.
whether the DOA-angle or a magnitude of the DOA-angle relative to the first listening
position is smaller than the magnitude of the border angle or angular width y, or whether
the original direction-of-arrival parameter is outside the window of interest, e.g. whether
the DOA-angle or a magnitude of the DOA-angle relative to the first listening position is
larger than the magnitude of the border angle or angular width y. This is also referred to as
direction-dependent and the corresponding filter functions as direction dependent filter
functions, wherein the angular width or border angle 7 defines the angle at which the
corresponding filter changes from increasing the parameter to decreasing the parameter or
vice versa.
Referring back to the diffuseness modification unit 301b, the diffuseness modification unit
301b is adapted to modify the diffuseness ? by the function fd(k,n,f,d) or fd which is
dependent on the time/frequency indices k,n, the original direction-of-arrival f, and the
zoom controller d. Fig. 5B shows an embodiment of a filter function fd. The filter fd may be
implemented as an inversion of the filter function H1, which will be explained later,
however, adapted to match the diffuseness range, for example the range between [0..1].
Fig. 5B shows the mapping function or filter fd, wherein the x-axis represents the original
or first diffuseness ?, in Fig. 5B also referred to as ?in, with the range from 0 to 1, and the
y-axis represents the second or modified diffuseness ymod also in the range of 0 to 1. In
case no zoom is applied (d = 0), the filter fd does not change the diffuseness at all and is set
to bypass, i.e. ?mod = ?in respectively. Reference sign 552 depicts the bypass line.
If the original direction-of-arrival lies within the angular width ?, the diffuseness is
decreased. If the original direction-of-arrival is outside the angular width ?, the diffuseness
is increased. Fig. 5B shows some prototype functions of fd, namely 562, 564, 572 and 574
depending on the look width or angular width ?. In the example shown in Fig. 5B the
angular width is smaller for ?2 than for ?1, i.e. ?2 < ?1. Thus, ?2 corresponds to a higher
zoom factor d than ?1.
The area below the bypass line 552 defines the modified diffuseness values ?mod in case
the original direction-of-arrival f is within the angular width ? which is reflected by a
reduction of the modified diffuseness value ?mod compared to the original diffuseness
value ?in or ? after the mapping by the filter fd. The area above the bypass line 552
represents the mapping of the original diffuseness ? to the modified diffuseness values
?mod in case the original direction-of-arrival f is outside the window. In other words, the
area above the bypass line 552 shows the increase of the diffuseness after the mapping. In
preferred embodiments, the angular width ? decreases with an increasing zoom factor d. In
other words, the higher a zoom factor d, the smaller the angular width y. In addition,
embodiments can be adapted such that the zoom factor d or translation information not
only influences the angular width ? of the filter function fd but also the degree or factor the
diffuseness is increased in case it is inside the window and the degree or factor the
diffuseness ? is decreased in case it is outside the window defined by the angular width y.
Such an embodiment is shown in Fig. 5B, wherein the angular width ?1 corresponds to a
zoom factor d1, and the angular width ?2 corresponds to a zoom factor d2, wherein d2 is
larger than d1 and, thus, the angular width ?2 is smaller than angular width ?1. In addition,
the function fd represented by reference sign 564 and corresponding to the larger zoom
factor d2 maps the original diffuseness values ?in to lower modified diffuseness values ?mod
than the filter function fd represented by 562 corresponding to the lower zoom factor d1. In
other words, embodiments of the filter function can be adapted to reduce the original
diffuseness the more the smaller the angular width 7. The corresponding applies to the area
above the bypass line 552 in an inverse manner. In other words, embodiments of the filter
function fd can be adapted to map the original diffuseness ?in to the modified diffuseness
?mod dependent on the zoom factor d and the angular width ?, or the higher the zoom factor
d the smaller the angular width ? and/or the higher the increase of the diffuseness for
direction-of-arrival f outside the window.
In further embodiments, the same direction dependent window or filter function fd(k,n,f,d)
is applied for all zoom factors. However, the use of different direction dependent window
or filter functions with smaller angular widths for higher translation or zoom factors
matches the audio experience of the user better and provides a more realistic audio
perception. The application of different mapping values for different zoom factors (higher
reduction of the diffuseness with increasing zoom factor for direction-of-arrival value f
inside the window, and increasing or higher diffuseness values for higher zoom factors in
case the direction-of-arrival value f is outside the angular width ?) even further improve
the realistic audio perception.
In the following, embodiments of the downmix modification as, for example, performed by
the downmix modification unit 302, are described in more detail.
The filters for the downmix signal are used to modify the gain of the direct and diffuse part
of the output signal. As a direct consequence of the spatial audio coder concept, the
loudspeaker signals are thus modified. The sound of the zoomed-in area is amplified, while
sound from out-of-interest directions can be attenuated.
As the downmix signal 112 may be a mono or a stereo signal for directional audio coding
(DirAC) or spatial audio microphones (SAM), in the following, two different embodiments
of the modification are described.
First, an embodiment for a mono downmix modification, i.e. an embodiment for a
modification of a mono downmix audio signal W 112 is described. For the following
considerations, it is useful to introduce a signal model of the mono downmix signal W(k,n)
which is similar to the one already applied for the loudspeaker signal synthesis according
to(1):

Here, S(k,n) denotes the direct sound component of the downmix signal, N(k,n) denotes the
diffuse sound components in the original downmix signal, and k denotes the time index or
time instant the signal represents and n represents a frequency bin or frequency channel of
the signal at the given time instant k.
Let Wmod(k,n) denote the modified mono downmix signal. It is obtained by processing the
original downmix signal according to

where Hl(k,n,f,d) and H2(k,n,f,d) represent filters applied to the direct and the diffuse
components of the signal model, f represents the original direction-of-arrival and d the
zoom factor or zoom parameter. The direct 112a and diffuse sound components 112b can
be computed analogously to (2), (3), i.e. by

and

Both filters are directional dependent weighting functions. For example, a cardioid shaped
pickup pattern of a microphone can be taken as a design criterion for such weighting
functions.
The filter Hi(k,n,f,d) can be implemented as a raised cosine window such that the direct
sound is amplified for directions of the zoomed-in area, whereas the level of sound coming
from other directions is attenuated. In general, different window shapes can be applied to
the direct and the diffuse sound components, respectively.
The gain filter implemented by the windows may be controlled by the actual translation or
zoom control factor d. For example, the zoom controls the width of equal gain for the
focused directions and the width of gain in general. Examples for different gain windows
are given in Fig. 6.
Fig. 6 shows different gain windows for the weighting filter H1(k,n,f,d). Four different
gain prototypes are shown:
1. solid line: no zoom is applied, the gain is 0 dB for all directions (see 612).
2. dashed line: a zoom factor of 1.3 is applied, the window width has a width of 210°
for the maximal gain and the maximal gain is 2.3 dB (see 614).
3. dotted line: a zoom factor of 2.1 is applied, the window width for the maximal gain
is decreased to 140° and the maximal gain is 3 dB, the lowest -2.5 dB (see 616).
4. dash-dotted line: the zoom factor is 2.8, the window width is 30° for the maximal
gain and the gain is limited to a maximum of +3 dB and a minimum of -6 dB (see
618).
As can be seen from Fig. 6, the first listening orientation represented by 0° in Fig. 6, forms
the center of different zoom factor dependent direction dependent windows, wherein the
predetermined central range or width of the direction dependent windows is the smaller the
greater the zoom factor. The borders of the central range or window are defined by the
angle y at which the gain is 0 dB. Fig. 6 shows symmetric windows with positive and
negative borders having the same magnitude.
Window 614 has a width of 210° for the maximum gain and a predetermined central region
with a width of 260° with borders +/- ?2 at +/- 130°, wherein direct components inside or
within the predetermined central region are increased and direct components outside of the
predetermined central region remain unamended (gain = 0 dB).
Window 616 has a width of 140° for the maximum gain and a predetermined central region
with a width of 180° with borders or angular widths +/- ?3 at +/- 90°, wherein direct
components inside or within the predetermined central region are increased and direct
components outside of the predetermined central region are reduced (negative gain down
to -2.5dB).
Window 618 has a width of 30° for the maximum gain and a predetermined central region
with a width of 60° with borders or angular widths +/- ?4 at +/- 30°, wherein direct
components inside or within the predetermined central region are increased and direct
components outside of the predetermined central region are reduced (negative gain down
to -6dB).
In certain embodiment, therefore, the zoom factor d controls the width, i.e. the negative
and positive borders and the total width, and the gain of the prototype windows. Thus, the
window can already be designed such that the width and the gain is correctly applied to the
original direction-of-arrivals f.
The maximal gain should be limited, in order to avoid distortions in the output signals. The
width of the window, or the exact shape as shown here should be considered as an
illustrative example of how the zoom factor controls various aspects of a gain window.
Other implementation may be used in different embodiments.
The filter H2(k,n,f,d) is used to modify the diffuse part 112a of the downmix signal
analogously to the way how the diffuseness measure ?(k,n) has been modified and can be
implemented as a subcardioid window as shown in Fig. 7. By applying such windows the
diffuse part from the out-of-interest directions are attenuated slightly, but the zoomed-in
directions remain unchanged or nearly unchanged. Fig. 7 shows a subcardioid window 702
which almost keeps the diffuse component unaltered in an area between -30° and +30° of
the original direction of arrival f and attenuate the diffuse component the higher the
deviation, i.e. the angle departing from the 0° orientation, of the original direction-of-
arrival f. In other words, for the zoomed-in area, the diffuse signal components in the
downmix signal remain unaltered. This will result in a more direct sound reproduction in
zoom direction. The sounds that come from all other directions are rendered more diffuse,
as the microphone has been virtually placed farther away. Thus, those diffuse parts will be
attenuated compared to those of the original downmix signal. Obviously, the desired gain
filter can also be designed using the previously described raised cosine windows. Note,
however, that the scaling will be less pronounced than in case of the direct sound
modification. In further embodiments, the windows can depend on the zoom factor,
wherein the slope of the window function 702 is the steeper the higher the zoom factor.
In the following, an embodiment of a stereo downmix modification, i.e. a modification of a
stereo downmix signal W is described.
In the following it is described how the downmix modification has to be performed in case
of a stereo downmix as required for the SAM approach. For the original stereo downmix
signal a two channels signal model analogously to the mono case (6) is introduced:

Again, the signal S(k,n) represents direct sound, while Nt denotes the diffuse sound for the
i-th microphone. Analogously to (2), (3), the direct and diffuse sound components can be
determined from the downmix channels based on the diffuseness measure. The gain factor
c corresponds to a different scaling of the direct sound component in the different stereo
channels, which arises from the different directivity pattern associated with the two
downmix channels. More details on the relation of the scaling factor and the DOA of direct
sound can be found in SAM. Since this scaling depends on the DOA of sound of the
observed sound field, its value has to be modified in accordance to the DOA remapping
resulting from the modified virtual recording location.
The modified stereo downmix signal corresponding to the new virtual microphone position
can be written as

The computation of the gain filters Gij(k,n,f,d) is performed in accordance to the
corresponding gain filters Hi(k,n,f,d) as discussed for the mono downmix case. The new
stereo scaling factor cmod is determined as a function of the modified DOA such that it
corresponds to the new virtual recording location.
Referring back to Figs. 2 and 3A, embodiments of the present invention provide an
apparatus 300 for converting a first parametric spatial audio signal 112, 114 representing a
first listening position or a first listening orientation in a spatial audio scene to a second
parametric spatial audio signal 212, 214 representing a second listening position or a
second listening orientation, the second listening position or second listening orientation
being different to the first listening position or first listening orientation. The apparatus
comprises a spatial audio signal modification unit 301, 302 adapted to modify the first
parametric spurious audio signal 112, 114 dependent on a change of the first listening
position or the first listening orientation so as to obtain the second parametric spatial audio
signal 212, 214, wherein the second listening position or the second listening orientation
corresponds to the first listening position or the first listening orientation changed by the
change.
Embodiments of the apparatus 300 can be adapted to convert only a single side information
parameter, for example, the direction-of-arrival 114a or the diffuseness parameter 114b, or
only the audio downmix signal 112 or some or all of the aforementioned signals and
parameters.
As described before, in embodiments using the directional audio coding (DirAC), the
analog microphone signals are digitized and processed to provide a downmixed
time/frequency representation W(k,n) of the microphone signals, representing, for each
time instant or block k, a frequency representation, wherein each frequency bin of the
frequency or spectral representation is denoted by the index n. In addition to the downmix
signal 112, the spatial audio analysis unit 100 determines for each time instant k and for
each frequency bin n for the corresponding time instant k, one unit vector edoa (confer
equation (4)) providing for each frequency bin n and each time instant k, the directional
parameter or information. In addition, the spatial audio analysis unit 100 determines for
each time instant k and each frequency bin n, a diffuseness parameter ? defining a relation
between the direct sound or audio components and the diffuse sound or audio components,
wherein the diffuse components are, for example, caused by two or more audio sources
and/or by reflections of audio signals from the audio sources.
The DirAC is a very processing efficient and memory efficient coding as it reduces the
spatial audio information defining the audio scene, for example, audio sources, reflection,
position and orientation of the microphones and respectively the listener (for each time
instant k and each frequency bin n) to one directional information, i.e. a unit vector
eDOA(k,n) and one diffuseness value ?(k,n) between 0 and 1, associated to the
corresponding one (mono) downmix audio signal W(k,n) or several (e.g. stereo) downmix
audio signals W1(k,n) and W2(k,n).
Embodiments using the aforementioned directional audio coding (DirAC) are, therefore,
adapted to modify, for each instant k and each frequency bin n, the corresponding
downmix value W(k,n) to Wmod(k,n), the corresponding direction-of-arrival parameter value
e(k,n) to emod(k,n) (in Figs. 1 to 3 represented by f, respectively fmod) and/or diffuseness
parameter value ?(k,n) to ?mod(k,n).
The spatial audio signal modification unit comprises or is formed by, for example, the
parameter modification unit 301 and the downmix modification unit 302. According to a
preferred embodiment, the parameter modification unit 301 is adapted to process the
original parameter 114a to determine the modified directional parameter 214a, to process
the diffuseness parameter ? depending on the original directional parameter f, respectively
114a, to split the downmix signal 112 using equations (2) and (3) using the original
diffuseness parameter ?, respectively 114b, and to apply the direction dependent filtering
H1(k,n,f,d) and H2(k,n,f,d) dependent on the original directional parameter f, respectively4
114a. As explained previously, these modifications are performed for each time instant k
and each frequency bin n to obtain, for each time instant k and each frequency instant n,
the respective modified signals and/or parameters.
According to one embodiment, the apparatus 300 is adapted to only modify the first
directional parameter 114a of the first parametric spatial audio signal to obtain a second
directional parameter 214a of the second parametric spatial audio signal depending on the
control signal 402, for example, a rotation control signal or a zoom control signal. In case
the change of the listening position/orientation only comprises a rotation and no translation
or zoom, a corresponding modification or shift of the directional parameter f(k,n) 114a is
sufficient. The corresponding diffuseness parameters and downmix signal components can
be left un-amended so that the second downmix signal 212 corresponds to the first
downmix signal 112 and the second diffuseness parameter 214b corresponds to the first
diffuseness parameter 114b.
In case of a translational change, for example a zoom, is performed, a modification of the
directional parameter f(k,n) 114a according to a remapping function as shown in Fig. 5A
already improves the sound experience and provides for a better synchronization between
the audio signal and, for example, a video signal compared to the unmodified or original
parametric spatial audio signal (without modifying the diffuseness parameter or the
downmix signal).
The above two embodiments which only comprise adapting or remapping the direction-of-
arrival by the filter fp already provide a good impression of the zooming effect.
According to another embodiment, the apparatus 300 is adapted to only apply filter
H1(k,n,f,d). In other words, this embodiment does not perform direction-of-arrival
remapping or diffuseness modification. This embodiment is adapted to only determine, for
example, the direct component 112a from the downmix signal 112 and to apply the filter
function H1 to the direct component to produce a direction dependent weighted version of
the direct component. Such embodiments may be further adapted to use the direction
dependent weighted version of the direct component as modified downmix signal Wmod
212, or to also determine the diffuse component 112b from the original downmix signal W
112 and to generate the modified downmix signal Wmod 212 by adding, or in general
combining, the direction dependent weighted version of the direct component and the
original or unaltered diffuse component 112b. An improved impression of the acoustic
zooming can be achieved, however, the zoom effect is limited because the direction-of-
arrival is not modified.
In an even further embodiment, the filters H1(k,n,f,d) and H2(k,n,f,d) are both applied,
however, no direction-of-arrival remapping or diffuseness modification is performed. The
acoustic impression is improved compared to the unamended or original parametric spatial
audio signal 112, 114. The zooming impression is also better than only applying filter
function H1(k,n,f,d) to the direct component when diffuse sound is present, however, is
still limited, because the direction-of-arrival f is not modified (better than the
aforementioned embodiment using only H1(k,n,f,d),.
In an even further embodiment, only the filter fd is applied, or in other words, only the
diffuseness component ? is modified. The zooming effect is improved compared to the
original parametric spatial audio signal 112, 114 because the diffuseness of zoomed in
areas (areas of interest) are reduced and the diffuseness values of out-of-interest are
increased.
Further embodiments are adapted to perform the remapping of the direction-of-arrival f by
the filter function fp in combination with applying the filter H1(k,n,f,d) alone. In other
words, such embodiments do not perform a diffuseness modification according to the filter
function fd and do not apply the second filter function H2(k,n,f,d) to a diffuse component
of the original downmix signal W 112. Such embodiments provide a very good zoom
impression that is better than only applying the direction-of-arrival remapping.
Embodiments applying the direction-of-arrival remapping according to function fp in
combination with a downmix modification using both filter functions H1(k,n,f,d) and
H2(k,n,f,d) provide even better zoom impressions than only applying the direction-of-
arrival remapping combined with applying the first filter function H1 alone.
Applying the direction-of-arrival remapping according to function fp, the downmix
modification using filters H1(k,n,f,d) and H2(k,n,f,d), and the diffuseness medication
using function fd provides the best acoustical zoom implementation.
Referring back to the embodiment remapping only the direction-of-arrival, additionally
modifying the diffuseness parameter 114b further improves the audio experience or, in
other words, improves the adaptation of the sound experience with regard to the changed
position within the spatial audio scene. Therefore, in further embodiments, the apparatus
300 can be adapted to only modify the directional parameter f(k,n) and the diffuseness
parameter ?(k,n), but not to modify the downmix signal W(k,n) 100.
Preferred embodiments of the apparatus 300 as mentioned above also comprise modifying
the downmix signal W(k,n) to even further improve the audio experience with regard to the
changed position in the spatial audio scene.
Therefore, in embodiments, wherein the first directional parameter f(k,n) 114a is a vector,
the parameter modification unit 301 is adapted to shift or modify the first directional
parameter by an angle defined by a rotation control signal in a reverse direction to a
direction defined by the rotation control signal to obtain the second directional parameter
fmod(k,n) 214a.
In further embodiments, the parameter modification unit 301 is adapted to obtain the
second directional parameter 214a using a non-linear mapping function (as, for example,
shown in Fig. 5 A) defining the second directional parameter 214a depending on the first
directional parameter f(k,n) and a zoom factor d defined by a zoom control signal 402 or
another translational control information defined by the change signal.
As described above, in further embodiments, the parameter modification unit 301 can be
adapted to modify the first diffuseness parameter ?(k,n) 114b of the first parametric spatial
audio signal to obtain a second diffuseness parameter ?mod(k,n) 214b depending on the first
directional parameter f(k,n) 114a. The parameter modification unit can be further adapted
to obtain the second diffuseness parameter ?mod(k,n) using a direction dependent function
adapted to decrease the first diffuseness parameter ?(k,n) to obtain the second diffuseness
parameter ?mod(k,n) in case the first directional parameter f(k,n) is within a predetermined
central range, for example y = +/- 30° of the original reference orientation (see Fig. 5B),
and/or to increase the first diffuseness parameter ?(k,n) to obtain the second diffuseness
parameter ?mod(k,n) in case the first directional parameter f(k,n) is outside of the
predetermined central range, for example, in a two-dimensional case outside the central
range defined by + ? = +30° and - ? = -30° from the 0° original reference orientation.
In other words, in certain embodiments the parameter modification unit 301, 310b is
adapted to obtain the second diffuseness parameter 214b using a direction dependent
function adapted to decrease the first diffuseness parameter 114b to obtain the second
diffuseness parameter 214b in case the first directional parameter 114a is within a
predetermined central range of the second directional parameter with the second or
changed listening orientation forming the center of the predetermined two-dimensional or
three-dimensional central range and/or to increase the first diffuseness parameter 114b to
obtain the second diffuseness parameter in case the first directional parameter 114a is
outside of the predetermined central range. The first or original listening orientation
defines a center, e.g. 0°, of the predetermined central range of the first directional
parameter, wherein a positive and a negative border of the predetermined central range is
defined by a positive and a negative angle y in a two-dimensional (e.g. horizontal) plane
(e.g. +/-30°) independent of whether the second listening orientation is a two-dimensional
or a three-dimensional vector, or by a corresponding angle ? (e.g. 30°) defining a right
circular cone around the three-dimensional first listening orientation. Further embodiments
can comprise different predetermined central regions or windows, symmetric and
asymmetric, arranged or centered around the first listening orientation or a vector defining
the first listening orientation.
In further embodiments, the direction-dependent function fd(k,n,f,d) depends on the
change signal, for example, the zoom control signal, wherein the predetermined central
range, respectively the values y defining the negative and positive border (or in general the
border) of the central range is the smaller the greater the translational change or the higher
the zoom factor defined by the zoom control signal is.
In further embodiments, the spatial audio signal modification unit comprises a downmix
modification unit 302 adapted to modify the first downmix audio signal W(k,n) of the first
parametric spatial audio signal to obtain a second downmix signal Wmod(k,n) of the second
parametric spatial audio signal depending on the first directional parameter f(k,n) and the
first diffuseness parameter ?(k,n). Embodiments of the downmix modification unit 302 can
be adapted to split the first downmix audio signal W into a direct component S(k,n) 112a
and a diffuse component N(k,n) 112b dependent on the first diffuseness parameter ?(k,n),
for example, based on equations (2) and (3).
In further embodiments, the downmix modification unit 302 is adapted to apply a first
direction dependent function H1(k,n,f,d) to obtain a direction dependent weighted version
of the direct component and/or to apply a second direction dependent function H2(k,n,f,d)
to the diffuse component to obtain a direction-dependent weighted version of the diffuse
component. The downmix modification unit 302 can be adapted to produce the direction
dependent weighted version of the direct component 112a by applying a further direction
dependent function H1(k,n,f,d) to the direct component, the further direction dependent
function being adapted to increase the direct component 112a in case the first directional
parameter 114a is within the further predetermined central range of the first directional
parameters and/or to decrease the direct component 112a in case the first directional
parameter 114a is outside of the further predetermined range of the second directional
parameters. In even further embodiments the downmix modification unit can be adapted to
produce the direction dependent weighted version of the diffusecomponent 112b by
applying a direction dependent function H2(k,n,f,d) to the diffuse component 112b, the
direction dependent function being adapted to decrease the diffuse component in case the
first directional parameter 114a is within a predetermined central range of the first
directional parameters and/or to increase the diffuseness component 112b in case the first
directional parameter 114a is outside of the predetermined range of the second directional
parameters.
In other embodiments, the downmix modification unit 302 is adapted to obtain the second
downmix signal 212 based on a combination, e.g. a sum, of a direction dependent weighted
version of the direct component 112a and a direction dependent weighted version of the
diffuse component 112b. However, further embodiments may apply other algorithms than
summing the two components to obtain the modified downmix signal 212.
As explained previously, embodiments of the downmix modification unit 302 can be
adapted to split up the downmix signal W into a diffuse part or component 112b and a non-
diffuse or direct part or component 112a by two multiplicators, namely (?)1/2 and (1 -?)1/2
and to filter the non-diffuse part 112a by filter function H1 and to filter the diffuse part
112b by filter function H2. The filter function H1 or H1(k,n,f,d) can be dependent on the
time/frequency indices k, n, the original direction-of-arrival f and the zoom parameter d.
The filter function H1 may be additionally dependent on the diffuseness ?. The filter
function H2 or H2(k,n,f,d) can be dependent on the time/frequency indices k, n, the
original direction-of-arrival f, and the zoom parameter d. The filter function H2 may be
additionally dependent on the diffuseness ?. As was described previously, the filter
function H2 can be implemented as a subcardioid window as shown in Fig. 7, or as a
simple attenuation factor, independent of the direction-of-arrival f.
Referring to the above explanations, the zoom parameter d can be used to control the filters
H1, H2 and the modifiers or functions fd and fp (see Fig. 3A). For the filter function H1 and
fd the zoom parameter d can also control the look width or angular width ? (also referred to
as border angle ?) of the applied windows or central regions. The width ? is defined, e.g. as
the angle at which the filter function has 0 dB (see e.g. the 0 dB line in Fig. 6). The angular
width ? and/or the gain can be controlled by the zoom parameter d. An example of
different values for y and different maximum gains and minimum gains is given in Fig. 6.
While embodiments of the apparatus have been described above, wherein the direction
dependent functions and weighting depend on the first or original directional parameter f
(see Fig. 3A), other embodiments can be adapted to determine the second or modified
diffuseness ?mod and/or one or both of the filter functions H1 and H2 dependent on the
second or modified directional parameter fmod. As can be determined from Fig. 4, where a
corresponds to the original directional parameter f and ß corresponds to the modified
directional parameter fmod (for zoom-in), the higher zoom factor d, the more object B
moves from a central or frontal position to a side position, or even (in case of even higher
zoom factors d than shown in Fig. 4) to a position in the back of the virtually modified
position. In other words, the higher the zoom factor d, the more the magnitude of an
initially small angle representing a position in a frontal area of the listener increases,
wherein higher angles represent positions in a side area of the listener. This modification of
the directional parameter is taken into account by applying a function as shown in Fig. 5A.
In addition, the direction dependent windows or functions for the other parameters and for
the direct and diffuse components can also be designed to take into account the
modification of the original directional parameter or angle, by reducing the angular width ?
with increasing zoom d, for example in a non-linear manner corresponding to the direction-
of-arrival or directional parameter mapping as shown in Fig. 5A. Therefore, these direction
dependent windows or functions can be adapted such that the original directional
parameter can be directly used (e.g. without prior modification by function fp), or
alternatively, first the directional parameter mapping fp is performed and afterwards the
direction dependent weighting fd, H1 and/or H2 based on the modified directional
parameter is performed in a similar manner. Referring to Fig. 4 again, thus, both is
possible, directional dependent functions fd, H1 and H2 referring directly to a, representing
the original directional parameter (for zoom-in), or directional dependent functions fd, H1
and H2 referring to p representing the modified directional parameter.
Embodiments using the modified directional parameter can employ, similar to the
embodiments using the original directional parameter, different windows with different
angular widths and/or different gains for different zoom factors, or, the same windows with
the same angular width (because the directional parameter has already been mapped to
reflect the different zoom factors) and the same gain, or windows with the same angular
widths but different gains, wherein a higher zoom factor results in a higher gain (analog to
the windows in Fig. 6).
Fig. 3B shows a further embodiment of the apparatus. The spatial audio signal
modification unit in Fig. 3B comprises or is formed by, for example, the parameter
modification unit 301 and the downmix modification unit 302. According to an alternative
embodiment, the parameter modification unit 301 is adapted to first process the original
parameter 114a to determine the modified directional parameter 214a, to then process the
diffuseness parameter ? depending on the modified directional parameter fmod,
respectively 214a, to split the downmix signal 112 using equations (2) and (3) and the
original diffuseness parameter ?, respectively 114b as described based on Fig. 3A, and to
apply the direction dependent filtering H1 and H2 dependent on the modified directional
parameter fmod, respectively 214a. As explained previously, these modifications are
performed for each time instant k and each frequency bin n to obtain, for each time instant
k and each frequency instant n, the respective modified signals and/or parameters.
According to another alternative embodiment of the apparatus 300 according to Fig. 3B,
the parameter modification unit 301 is adapted to process the original parameter 114a to
determine the modified directional parameter 214a, to process the diffuseness parameter ?
depending on the original directional parameter f or 114a, to determine the modified
diffuseness parameter ?mod or 214b, to split the downmix signal 112 using equations (2)
and (3) and the original diffuseness parameter ? or 114b as described based on Fig. 3A,
and to apply the direction dependent filtering H1 and H2 dependent on the modified
directional parameter fmod, or 214a.
According to one embodiment, the apparatus 300 according to Fig. 3B is adapted to only
modify the first directional parameter 114a of the first parametric spatial audio signal to
obtain a second directional parameter 214a of the second parametric spatial audio signal
depending on the control signal 402, for example, a rotation control signal or a zoom
control signal. In case the change of the listening position/orientation only comprises a
rotation and no translation or zoom, a corresponding modification or shift of the directional
parameter f(k,n) 114a is sufficient. The corresponding diffuseness parameters and
downmix signal components can be left un-amended so that the second downmix signal
212 corresponds to the first downmix signal 112 and the second diffuseness parameter
214b corresponds to the first diffuseness parameter 114b.
In case of a translational change, for example a zoom, is performed, a modification of the
directional parameter f(k,n) 114a according to a remapping function as shown in Fig. 5A
already improves the sound experience and provides for a better synchronization between
the audio signal and, for example, a video signal compared to the unmodified or original
parametric spatial audio signal (without modifying the diffuseness parameter or the
downmix signal).
Modifying the diffuseness parameter 114b further improves the audio experience or, in
other words, improves the adaptation of the sound experience with regard to the changed
position within the spatial audio scene. Therefore, in further embodiments, the apparatus
300 can be adapted to only modify the directional parameter f(k,n) and the diffuseness
parameter ?(k,n), the latter dependent on the modified directional parameter fmod(k,n), but
not to modify the downmix signal W(k,n) 100.
Preferred embodiments of the apparatus 300 according to Fig. 3B also comprise modifying
the downmix signal W(k,n) dependent on the original diffuseness ?(k,n) and the modified
directional parameter fmod(k,n) to even further improve the audio experience with regard to
the changed position in the spatial audio scene.
Therefore, in embodiments, wherein the first directional parameter f(k,n) 114a is a vector,
the parameter modification unit 301 is adapted to shift or modify the first directional
parameter by an angle defined by a rotation control signal in a reverse direction to a
direction defined by the rotation control signal to obtain the second directional parameter
fmod(k,n) 214a.
In further embodiments, the parameter modification unit 301 is adapted to obtain the
second directional parameter 214a using a non-linear mapping function (as, for example,
shown in Fig. 5A) defining the second directional parameter 214a depending on the first
directional parameter f(k,n) and a zoom factor d defined by a zoom control signal 402 or
another translational control information defined by the change signal.
As described above, in further embodiments, the parameter modification unit 301 can be
adapted to modify the first diffuseness parameter ?(k,n) 114b of the first parametric spatial
audio signal to obtain a second diffuseness parameter ?mod(k,n) 214b depending on the
second directional parameter fmod(k,n) 214a. The parameter modification unit can be
further adapted to obtain the second diffuseness parameter ?mod(k,n) using a direction
dependent function adapted to decrease the first diffuseness parameter ?(k,n) to obtain the
second diffuseness parameter ?mod(k,n) in case the second directional parameter fmod(k,n)
is within a predetermined central range, for example +/- 30° of the original reference
orientation referred to as original 0° orientation, and/or to increase the first diffuseness
parameter ?(k,n) to obtain the second diffuseness parameter ?mod(k,n) in case the second
directional parameter fmod(k,n) is outside of the predetermined central range, for example,
in a two-dimensional case outside the central range defined by +30° and -30° from the 0°
original reference orientation.
In other words, in certain embodiments the parameter modification unit 301, 310b is
adapted to obtain the second diffuseness parameter 214b using a direction dependent
function adapted to decrease the first diffuseness parameter 114b to obtain the second
diffuseness parameter 214b in case the second directional parameter 214a is within a
predetermined central range of the second directional parameter with the first or original
listening orientation forming the center of the predetermined two-dimensional or three-
dimensional central range and/or to increase the first diffuseness parameter 114b to obtain
the second diffuseness parameter in case the second directional parameter 214a is outside
of the predetermined central range. The first listening orientation defines a center, e.g. 0°,
of the predetermined central range of the second directional parameter, wherein a positive
and a negative border of the predetermined central range is defined by a positive and a
negative angle in a two-dimensional (e.g. horizontal) plane (e.g. +/-30°) independent of
whether the first listening orientation is a two-dimensional or a three-dimensional vector,
or by a corresponding angle (e.g. 30°) defining a right circular cone around the three-
dimensional second listening orientation. Further embodiments can comprise different
predetermined central regions, symmetric and asymmetric, arranged around the first
listening orientation or vector defining the first listening orientation.
In further embodiments, the direction-dependent function fd(?) depends on the change
signal, for example, the zoom control signal, wherein the predetermined central range,
respectively the values defining the negative and positive border (or in general the border)
of the central range is the smaller the greater the translational change or the higher the
zoom factor defined by the zoom control signal is.
In further embodiments, the spatial audio signal modification unit comprises a downmix
modification unit 302 adapted to modify the first downmix audio signal W(k,n) of the first
parametric spatial audio signal to obtain a second downmix signal Wmod(k,n) of the second
parametric spatial audio signal depending on the second directional parameter fmod(k,n)
and the first diffuseness parameter ?(k,n). Embodiments of the downmix modification unit
302 can be adapted to split the first downmix audio signal W into a direct component S(k,n)
112a and a diffuse component N(k,n) 112b dependent on the first diffuseness parameter
?(k,n), for example, based on equations (2) and (3).
In further embodiments, the downmix modification unit 302 is adapted to apply a first
direction dependent function H1 to obtain a direction dependent weighted version of the
direct component and/or to apply a second direction dependent function H2 to the diffuse
component to obtain a direction-dependent weighted version of the diffuse component. The
downmix modification unit 302 can be adapted to produce the direction dependent
weighted version of the direct component 112a by applying a further direction dependent
function H1 to the direct component, the further direction dependent function being
adapted to increase the direct component 112a in case the second directional parameter
214a is within the further predetermined central range of the second directional parameters
and/or to decrease the direct component 112a in case the second directional parameter
214a is outside of the further predetermined range of the second directional parameters. In
even further embodiments the downmix modification unit can be adapted to produce the
direction dependent weighted version of the diffuse component 112b by applying a
direction dependent function H2 to the diffuse component 112b, the direction dependent
function being adapted to decrease the diffuse component in case the second directional
parameter 214a is within a predetermined central range of the second directional
parameters and/or to increase the diffuse component 112b in case the second directional
parameter 214a is outside of the predetermined range of the second directional parameters.
In other embodiments, the downmix modification unit 302 is adapted to obtain the second
downmix signal 212 based on a combination, e.g. a sum, of a direction dependent weighted
version of the direct component 112a and a direction dependent weighted version of the
diffuse component 112b. However, further embodiments may apply other algorithms than
summing the two components to obtain the modified downmix signal 212.
As explained previously, embodiments of the downmix modification unit 302 according to
Fig. 3B can be adapted to split up the downmix signal W into a diffuse part or component
112b and a non-diffuse or direct part or component 112a by two multiplicators, namely
(?)1/2 and (1 - ?) ½ and to filter the non-diffuse part 112a by filter function H1 and to filter
the diffuse part 112b by filter function H2. The filter function H1 or H1(f, ?) can be
dependent on the time/frequency indices k, n, the modified direction-of-arrival and the
zoom parameter d. The filter function H1 may be additionally dependent on the diffuseness
?. The filter function H2 or H2(f, ?) can be dependent on the time/frequency indices k, n,
the original direction-of-arrival f, and the zoom parameter d. The filter function H2 or
H(f, ?) may be additionally dependent on the diffuseness ?. As was described previously,
the filter function H2 can be implemented as a subcardioid window as shown in Fig. 7, or
as a simple attenuation factor, independent of the modified direction-of-arrival fmod.
Referring to the above explanations, also in embodiments according to Fig. 3B, the zoom
parameters d can be used to control the filters H1, H2 and the modifiers or functions fd and
fp. For the filter functions H1 and fd the zoom parameter d can also control the angular
width ? (also referred to as border angle ?) of the applied windows or central regions. The
width ? is defined, e.g. as the angle at which the filter function has 0 dB (analog to the 0
dB line in Fig. 6). The angular width 7 and/or the gain can be controlled by the zoom
parameter d. It should be noted that in general, the explanations given with regard to the
embodiments according to Fig. 3A apply in the same manner or at least in an analog
manner to embodiments according to Fig. 3B.
In the following, exemplary applications are described where the inventive embodiments
lead to an improved experience of a joint video/audio playback by adjusting the perceived
audio image to the zoom control of a video camera.
In teleconferencing, it is state-of-the-art to automatically steer the camera towards the
active speaker. This is usually connected with zooming closer to the talker. The sound is
traditionally not matched to the picture. Embodiments of the present invention provide the
possibility of also zooming-in on the active talker acoustically. This was the overall
impression is more realistic for the far-end users, as not only the picture is changed in its
focus, but the sound matches the desired change of attention. In short, the acoustical cues
correspond to the visual cues.
Modern camcorders, for example, for home entertainment, are capable of recording
surround sound and have a powerful optical zoom. There is, however, no perceptual
equivalent interaction between the optical zoom and the recorded sound, as the recorded
spatial sound only depends on the actual position of the camera and, thus, the position of
the microphones mounted on the camera itself. In case of a scene filmed in a close-up
mode, the invention allows to adjust the audio image accordingly. This leads to a more
natural and consistent consumer experience as the sound is zoomed together with the
picture.
It should be mentioned that the invention may also be applied in a post-processing phase if
the original microphone signals are recorded unaltered with the video and no further
processing has been done. Although the original zoom length may not be known, the
invention can be used in creative audio-visual post-processing toolboxes. An arbitrary
zoom-length can be selected and the acoustical zoom can be steered by the user to match
the picture. Alternatively, the user can create his own preferred spatial effects. In either
case, the original microphone recording position will be altered to a user defined virtual
recording position.
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 disc, a CD, a DVD or a Blu-Ray
disc having an electronically-readable control signal stored thereon, which cooperates with
a programmable computer system such that an embodiment of the inventive method is
performed. Generally, an embodiment of the present invention is, therefore, a computer
program produced with a program code stored on a machine-readable carrier, the program
code being operative for performing the inventive method when the computer program
product runs on a computer. In other words, embodiments of the inventive method 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.
The afore-going was 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, therefore, to be understood that various changes may be made in adapting the
different embodiments without departing from the broader concept disclosed herein and
comprehended by the claims that follow.
Claims
as attached to IPER - clean copy
1. Apparatus (300) for converting a first parametric spatial audio signal (112, 114)
representing a first listening position or a first listening orientation in a spatial audio
scene to a second parametric spatial audio signal (212, 214) representing a second
listening position or a second listening orientation; the apparatus comprising:
a spatial audio signal modification unit (301, 302) adapted to modify the first
parametric spatial audio signal (112, 114) dependent on a change of the first
listening position or the first listening orientation so as to obtain the second
parametric spatial audio signal (212, 214), wherein the second listening position or
the second listening orientation corresponds to the first listening position or the first
listening orientation changed by the change,
wherein the first parametric spatial audio signal (112, 114) comprises a downmix
signal (112), a direction-of-arrival parameter (114a) and a diffuseness parameter
(114b), and
wherein the second parametric spatial audio signal comprises a downmix signal
(212), a direction-of-arrival parameter (214a) and a diffuseness parameter (214b).
2. Apparatus according to claim 1, wherein the spatial audio signal modification unit
(301, 302) comprises:
a parameter modification unit (301, 301a) adapted to modify a first directional
parameter (114a) of the first parametric spatial audio signal (112, 114) so as to
obtain a second directional parameter (214a) of the second parametric spatial audio
signal (212, 214) depending on a control signal (402) providing information
corresponding to the change.
3. Apparatus according to claim 2, wherein the first directional parameter (114a) and
the second directional parameter (214a) are two-dimensional or three-dimensional
vectors.
4. Apparatus according to claim 2 or 3, wherein the first directional parameter (114a)
is a vector, wherein the control signal is a rotation control signal defining a rotation
angle and a rotation direction, and wherein the parameter modification unit (301,
301a) is adapted to rotate the vector by the rotation angle in a reverse direction to
the rotation direction to obtain the second directional parameter (214a).
5. Apparatus according to one of the claims 2 to 4, wherein the control signal is a
translation control signal (402) defining a translation (d) in direction of the first
listening orientation, wherein the parameter modification unit (301, 301a) is
adapted to obtain the second directional parameter (214a) using a non-linear
mapping function (fp) defining the second directional parameter depending on the
first directional parameter (114a) and the translation (d) defined by the control
signal.
6. Apparatus according to one of the claims 2 to 4, wherein the control signal is a
zoom control signal (402) defining a zoom factor (d) in direction of the first
listening orientation, wherein the parameter modification unit (301, 301a) is
adapted to obtain the second directional parameter (214a) using a non-linear
mapping function (fp) defining the second directional parameter depending on the
first directional parameter (114a) and the zoom factor (d) defined by the zoom
control signal.
7. Apparatus according to one of the claims 2 to 6, wherein the parameter
modification unit (301, 301b) is adapted to modify a first diffuseness parameter
(114b) of the first parametric spatial audio signal so as to obtain a second
diffuseness parameter (214b) of the second parametric spatial audio signal
depending on the first directional parameter (114a) or depending on the second
directional parameter (214a).
8. Apparatus according to claim 7, wherein the parameter modification unit (301,
310b) is adapted to obtain the second diffuseness parameter (214b) using a
direction dependent function (fd) adapted to decrease the first diffuseness parameter
(114b) to obtain the second diffuseness parameter (214b) in case the first
directional parameter (114a) is within a predetermined central range of the first
directional parameter and/or to increase the first diffuseness parameter (114b) to
obtain the second diffuseness parameter in case the first directional parameter
(114a) is outside of the predetermined central range, or
wherein the parameter modification unit (301, 310b) is adapted to obtain the second
diffuseness parameter (214b) using a direction dependent function (fd) adapted to
decrease the first diffuseness parameter (114b) to obtain the second diffuseness
parameter (214b) in case the second directional parameter (214a) is within a
predetermined central range of the second directional parameter and/or to increase
the first diffuseness parameter (114b) to obtain the second diffuseness parameter in
case the second directional parameter (214a) is outside of the predetermined central
range.
9. Apparatus according to claim 8, wherein the control signal is a translation control
signal (402) defining a translation (d) in direction of the first listening orientation,
wherein the direction dependent function depends on the translation, and wherein
the predetermined central range is the smaller the greater the translation defined by
the translation control signal; or wherein the control signal is a zoom control signal
(402) defining a zoom in direction of the first listening orientation, wherein the
direction dependent function depends on the zoom, and wherein the predetermined
central range is the smaller the greater a zoom factor (d) defined by the zoom
control signal.
10. Apparatus according to claims 7 to 9, the spatial audio signal modification unit
(300) comprising:
a downmix modification unit (302) adapted to modify a first downmix audio signal
(112) of the first parametric spatial audio signal to obtain a second downmix signal
(212) of the second parametric spatial audio signal depending on the first
directional parameter (114a) and/or the first diffuseness parameter (114b), or
a downmix modification unit (302) adapted to modify the first downmix audio
signal (112) of the first parametric spatial audio signal to obtain the second
downmix signal (212) of the second parametric spatial audio signal depending on
the second directional parameter (214a) and/or the first diffuseness parameter
(114b).
11. Apparatus according to claim 10, wherein the downmix modification unit (302) is
adapted to derive a direct component (112a) from the first downmix audio signal
(112) and/or a diffuse component (112b) from the first downmix audio signal (112)
dependent on the first diffuseness parameter (114b).
12. Apparatus according to claim 11, wherein the downmix modification unit (302) is
adapted to determine the direct component (112a) by:

and/or the diffuse component by:

wherein k is a time index, n is a frequency bin index, W(k,n) refers to the first
downmix signal, ?(k,n) refers to the first diffuseness parameter, S(k,n) refers to the
direct component and N(k,n) refers to the diffuse component derived from the first
downmix signal.
13. Apparatus according to claim 11 or 12, wherein the downmix modification unit
(302) is adapted to obtain the second downmix signal (212) based on a direction
dependent weighted version of the direct component (112a), on a direction
dependent weighted version of the diffuse component (112b) or based on a
combination of the direction dependent weighted version of the direct component
(112a) and the direction dependent weighted version of the diffuse component
(112b).
14. Apparatus according to claim 13, wherein the downmix modification unit (302) is
adapted to produce the direction dependent weighted version of the direct
component (112a) by applying a further direction dependent function (H1) to the
direct component, the further direction dependent function being adapted to
increase the direct component (112a) in case the first directional parameter (114a)
is within a further predetermined central range of the first directional parameters
and/or to decrease the direct component (112a) in case the first directional
parameter (114a) is outside of the further predetermined range of the first
directional parameters.
15. Apparatus according to claim 13 or 14, wherein the downmix modification unit is
adapted to produce the direction dependent weighted version of the diffuse
component (112b) by applying a direction dependent function (H2) to the diffuse
component (112b),
the direction dependent function being adapted to decrease the diffuse component
in case the first directional parameter (114a) is within a predetermined central range
of the first directional parameters and/or to increase the diffuse component (112b)
in case the first directional parameter (114a) is outside of the predetermined range
of the first directional parameters, or
the direction dependent function being adapted to decrease the diffuse component
in case the second directional parameter (214a) is within a predetermined central
range of the second directional parameters and/or to increase the diffuse component
(112b) in case the second directional parameter (214a) is outside of the
predetermined range of the second directional parameters.
16. System comprising:
an apparatus according to one of the claims 1 to 15; and
a video camera, wherein the apparatus is coupled to the video camera and is
adapted to receive a video rotation or a video zoom signal as a control signal.
17. A method for converting a first parametric spatial audio signal (112, 114)
representing a first listening position or a first listening orientation in a spatial audio
scene to a second parametric spatial audio signal (212, 214) representing a second
listening position or a second listening orientation, the method comprising:
modifying the first parametric spatial audio signal dependent on a change of the
first listening position or the first listening orientation so as to obtain the second
parametric spatial audio signal, wherein the second listening position or the second
listening orientation corresponds to the first listening position or the first listening
orientation changed by the change;
wherein the first parametric spatial audio signal (112, 114) comprises a downmix
signal (112), a direction-of-arrival parameter (214a) and a diffuseness parameter
(114b), and
wherein the second parametric spatial audio signal comprises a downmix signal
(212), a direction-of-arrival parameter (214a) and a diffuseness parameter (214b).
18. A computer program having a program code for performing the method according
to claim 17 when the program runs on a computer.
19. Apparatus (300) for converting a first parametric spatial audio signal (112, 114)
representing a first listening position or a first listening orientation in a spatial audio
scene to a second parametric spatial audio signal (212, 214) representing a second
listening position or a second listening orientation; the apparatus comprising:
a spatial audio signal modification unit (301, 302) adapted to modify the first
parametric spatial audio signal (112, 114) dependent on a change of the first
listening position or the first listening orientation so as to obtain the second
parametric spatial audio signal (212, 214), wherein the second listening position or
the second listening orientation corresponds to the first listening position or the first
listening orientation changed by the change;
wherein the spatial audio signal modification unit (301, 302) comprises a parameter
modification unit (301, 301a) adapted to modify a first directional parameter (114a)
of the first parametric spatial audio signal (112, 114) so as to obtain a second
directional parameter (214a) of the second parametric spatial audio signal (212,
214) depending on a control signal (402) providing information corresponding to
the change; and
wherein the control signal is a translation control signal (402) defining a translation
(d) in direction of the first listening orientation, wherein the parameter modification
unit (301, 301a) is adapted to obtain the second directional parameter (214a) using
a non-linear mapping function (fp) defining the second directional parameter
depending on the first directional parameter (114a) and the translation (d) defined
by the control signal.
20. Apparatus (300) for converting a first parametric spatial audio signal (112, 114)
representing a first listening position or a first listening orientation in a spatial audio
scene to a second parametric spatial audio signal (212, 214) representing a second
listening position or a second listening orientation; the apparatus comprising:
a spatial audio signal modification unit (301, 302) adapted to modify the first
parametric spatial audio signal (112, 114) dependent on a change of the first
listening position or the first listening orientation so as to obtain the second
parametric spatial audio signal (212, 214), wherein the second listening position or
the second listening orientation corresponds to the first listening position or the first
listening orientation changed by the change;
wherein the spatial audio signal modification unit (301, 302) comprises a parameter
modification unit (301, 301a) adapted to modify a first directional parameter (114a)
of the first parametric spatial audio signal (112, 114) so as to obtain a second
directional parameter (214a) of the second parametric spatial audio signal (212,
214) depending on a control signal (402) providing information corresponding to
the change; and
wherein the control signal is a zoom control signal (402) defining a zoom factor (d)
in direction of the first listening orientation, wherein the parameter modification
unit (301, 301a) is adapted to obtain the second directional parameter (214a) using
a non-linear mapping function (fp) defining the second directional parameter
depending on the first directional parameter (114a) and the zoom factor (d) defined
by the zoom control signal.
21. Apparatus (300) for converting a first parametric spatial audio signal (112, 114)
representing a first listening position or a first listening orientation in a spatial audio
scene to a second parametric spatial audio signal (212, 214) representing a second
listening position or a second listening orientation; the apparatus comprising:
a spatial audio signal modification unit (301, 302) adapted to modify the first
parametric spatial audio signal (112, 114) dependent on a change of the first
listening position or the first listening orientation so as to obtain the second
parametric spatial audio signal (212, 214), wherein the second listening position or
the second listening orientation corresponds to the first listening position or the first
listening orientation changed by the change;
wherein the spatial audio signal modification unit (301, 302) comprises a parameter
modification unit (301, 301a) adapted to modify a first directional parameter (114a)
of the first parametric spatial audio signal (112, 114) so as to obtain a second
directional parameter (214a) of the second parametric spatial audio signal (212,
214) depending on a control signal (402) providing information corresponding to
the change;
wherein the spatial audio signal modification unit (300) comprises
a downmix modification unit (302) adapted to modify a first downmix audio signal
(112) of the first parametric spatial audio signal to obtain a second downmix signal
(212) of the second parametric spatial audio signal depending on the first
directional parameter (114a) and/or a first diffuseness parameter (114b), or
a downmix modification unit (302) adapted to modify the first downmix audio
signal (112) of the first parametric spatial audio signal to obtain the second
downmix signal (212) of the second parametric spatial audio signal depending on
the second directional parameter (214a) and/or a first diffuseness parameter (114b);
wherein the downmix modification unit (302) is adapted to derive a direct
component (112a) from the first downmix audio signal (112) and a diffuse
component (112b) from the first downmix audio signal (112) dependent on the first
diffuseness parameter (114b);
wherein the downmix modification unit (302) is adapted to obtain the second
downmix signal (212) based on a combination of a direction dependent weighted
version of the direct component (112a) and a direction dependent weighted version
of the diffuse component (112b);
wherein the downmix modification unit (302) is adapted to produce the direction
dependent weighted version of the direct component (112a) by applying a first
direction dependent function (H1) to the direct component, the first direction
dependent function being adapted to increase the direct component (112a) in case
the first directional parameter (114a) is within a predetermined central range of the
first directional parameters and/or to decrease the direct component (112a) in case
the first directional parameter (114a) is outside of the predetermined range of the
first directional parameters; and
wherein the downmix modification unit (302) is adapted to apply a second
direction-dependent function (H2) to the diffuse component to obtain a the
direction dependent weighted version of the diffuse component.
22. Apparatus (300) for converting a first parametric spatial audio signal (112, 114)
representing a first listening position or a first listening orientation in a spatial audio
scene to a second parametric spatial audio signal (212, 214) representing a second
listening position or a second listening orientation; the apparatus comprising:
a spatial audio signal modification unit (301, 302) adapted to modify the first
parametric spatial audio signal (112, 114) dependent on a change of the first
listening position or the first listening orientation so as to obtain the second
parametric spatial audio signal (212, 214), wherein the second listening position or
the second listening orientation corresponds to the first listening position or the first
listening orientation changed by the change;
wherein the spatial audio signal modification unit (301, 302) comprises a parameter
modification unit (301, 301a) adapted to modify a first directional parameter (114a)
of the first parametric spatial audio signal (112, 114) so as to obtain a second
directional parameter (214a) of the second parametric spatial audio signal (212,
214) depending on a control signal (402) providing information corresponding to
the change;
wherein the parameter modification unit (301, 301b) is adapted to modify a first
diffuseness parameter (114b) of the first parametric spatial audio signal so as to
obtain a second diffuseness parameter (214b) of the second parametric spatial audio
signal depending on the first directional parameter (114a) or depending on the
second directional parameter (214a).

ABSTRACT

An apparatus (300) for converting a first parametric spatial audio signal representing a first
listening position or a first listening orientation in a spatial audio scene to a second
parametric spatial audio signal (112, 114) representing a second listening position or a
second listening orientation is described, the apparatus comprising: a spatial audio signal
modification unit (301, 302) adapted to modify the first parametric spatial audio signal
(212, 214) dependent on a change of the first listening position or the first listening
orientation so as to obtain the second parametric spatial audio signal (212, 214), wherein
the second listening position or the second listening orientation corresponds to the first
listening position or the first listening orientation changed by the change.