AU2011247872B8 - An apparatus for determining a spatial output multi-channel audio signal - Google Patents

Description

AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION Standard Patent Applicant(s): Fraunhofer-Gesellschaft zur Foerderung der angewandten Forschung e.V. Invention Title: An apparatus for determining a spatial output multi-channel audio signal The following statement is a full description of this invention, including the best method for performing it known to me/us: - 2 An Apparatus for Determining a Spatial Output Multi Channel Audio Signal Related Application 5 This application is divided from and claims the benefit of the filing and priority dates of application no. 2009281356 filed 11 August 2009, the content of which as filed is incorporated herein by reference in its entirety. 10 Field of the Invention The present invention is in the field of audio processing, especially processing of spatial audio properties. Background of the Invention 15 Audio processing and/or coding has advanced in many ways. More and more demand is generated for spatial audio applications. In many applications audio signal processing is utilized to decorrelate or render signals. Such applications may, for example, carry out mono-to-stereo 20 up-mix, mono/stereo to multi-channel up-mix, artificial reverberation, stereo widening or user interactive mixing/rendering. For certain classes of signals as e.g. noise-like signals 25 as for instance applause-like signals, conventional methods and systems suffer from either unsatisfactory perceptual quality or, if an object-orientated approach is used, high computational complexity due to the number of auditory events to be modeled or processed. Other examples 30 of audio material, which is problematic, are generally ambience material like, for example, the noise that is emitted by a flock of birds, a sea shore, galloping horses, a division of marching soldiers, etc. 35 Conventional concepts use, for example, parametric stereo or MPEG-surround coding (MPEG = Moving Pictures Expert Group). Fig. 6 shows a typical application of a 29360771 (GHMatters) P88385 AU -3 decorrelator in a mono-to-stereo up-mixer. Fig. 6 shows a mono input signal provided to a decorrelator 610, which provides a decorrelated input signal at its output. The original input signal is provided to an up-mix matrix 620 5 together with the decorrelated signal. Dependent on up-mix control parameters 630, a stereo output signal is rendered. The signal decorrelator 610 generates a decorrelated signal D fed to the matrixing stage 620 along with the dry mono signal M. Inside the mixing matrix 620, 10 the stereo channels L (L = Left stereo channel) and R (R = Right stereo channel) are formed according to a mixing matrix H. The coefficients in the matrix H can be fixed, signal dependent or controlled by a user. 15 Alternatively, the matrix can be controlled by side information, transmitted along with the down-mix, containing a parametric description on how to up-mix the signals of the down-mix to form the desired multi-channel output. This spatial side information is usually generated 20 by a signal encoder prior to the up-mix process. This is typically done in parametric spatial audio coding as, for example, in Parametric Stereo, cf. J. Breebaart, S. van de Par, A. Kohlrausch, E. Schuijers, "High-Quality 25 Parametric Spatial Audio Coding at Low Bitrates" in AES 116th Convention, Berlin, Preprint 6072, May 2004 and in MPEG Surround, cf. J. Herre, K. Kj6rling, J. Breebaart, et. al., "MPEG Surround - the ISO/MPEG Standard for Efficient and Compatible Multi-Channel Audio Coding" in 30 Proceedings of the 122nd AES Convention, Vienna, Austria, May 2007. A typical structure of a parametric stereo decoder is shown in Fig. 7. In this example, the decorrelation process is performed in a transform domain, which is indicated by the analysis filterbank 710, which 35 transforms an input mono signal to the transform domain as, for example, the frequency domain in terms of a number of frequency bands. 2938077_1 (GHMatters) P8836S.AU -4 In the frequency domain, the decorrelator 720 generates the according decorrelated signal, which is to be up-mixed in the up-mix matrix 730. The up-mix matrix 730 considers 5 up-mix parameters, which are provided by the parameter modification box 740, which is provided with spatial input parameters and coupled to a parameter control stage 750. In the example shown in Fig. 7, the spatial parameters can be modified by a user or additional tools as, for example, 10 post-processing for binaural rendering/presentation. In this case, the up-mix parameters can be merged with the parameters from the binaural filters to form the input parameters for the up-mix matrix 730. The measuring of the parameters may be carried out by the parameter 15 modification block 740. The output of the up-mix matrix 730 is then provided to a synthesis filterbank 760, which determines the stereo output signal. As described above, the output LIR of the mixing matrix H 20 can be computer from the mono input signal M and the decorrelated signal D, for example according to [L] =[,. 2[

M

] R h kh D 25 In the mixing matrix, the amount of decorrelated sound fed to the output can be controlled on the basis of transmitted parameters as, for example, ICC (ICC = Interchannel Correlation) and/or mixed or user-defined settings. 30 Another conventional approach is established by the temporal permutation method. A dedicated proposal on decorrelation of applause-like signals can be found, for example, in Gerard Hotho, Steven van de Par, Jeroen 35 Breebaart, "Multichannel Coding of Applause Signals, " in 2938077_1 (GHMatters) P88385 AU -5 EURASIP Journal on Advances in Signal Processing, Vol. 1, Art. 10, 2008. Here, a monophonic audio signal is segmented into overlapping time segments, which are temporally permuted pseudo randomly within a "super"-block 5 to form the decorrelated output channels. The permutations are mutually independent for a number n output channels. Another approach is the alternating channel swap of original and delayed copy in order to obtain a 10 decorrelated signal, cf. German patent application 102007018032.4-55. In some conventional conceptual object-orientated systems, e.g. in Wagner, Andreas; Walther, Andreas; Melchoir, 15 Frank; Straug, Michael; "Generation of Highly Immersive Atmospheres for Wave Field Synthesis Reproduction" at 116th International EAS Convention, Berlin, 2004, it is described how to create an immersive scene out of many objects as for example single claps, by application of a 20 wave field synthesis. Yet another approach is the so-called "directional audio coding" (DirAC = Directional Audio Coding), which is a method for spatial sound representation, applicable for 25 different sound reproduction systems, cf. Pulkki, Ville, "Spatial Sound Reproduction with Directional Audio Coding" in J. Audio Eng. Soc., Vol. 55, No. 6, 2007. In the analysis part, the diffuseness and direction of arrival of sound are estimated in a single location dependent on time 30 and frequency. In the synthesis part, microphone signals are first divided into non-diffuse and diffuse parts and are then reproduced using different strategies. Conventional approaches have a number of disadvantages. 35 For example, guided or unguided up-mix of audio signals having content such as applause may require a strong decorrelation. Consequently, on the one hand, strong 29380771 (GHMatters) P86365.AU - 6 decorrelation is needed to restore the ambience sensation of being, for example, in a concert hall. On the other hand, suitable decorrelation filters as, for example, all pass filters, degrade a reproduction of quality of 5 transient events, like a single handclap by introducing temporal smearing effects such as pre- and post-echoes and filter ringing. Moreover, spatial panning of single clap events has to be done on a rather fine time grid, while ambience decorrelation should be quasi-stationary over 10 time. State of the art systems according to J. Breebaart, S. van de Par, A. Kohlrausch, E. Schuijers, "High-Quality Parametric Spatial Audio Coding at Low Bitrates" in AES 15 116th Convention, Berlin, Preprint 6072, May 2004 and J. Herre, K. Kj6rling, J. Breebaart, et. al., "MPEG Surround - the ISO/MPEG Standard for Efficient and Compatible Multi-Channel Audio Coding" in Proceedings of the 122nd AES Convention, Vienna, Austria, May 2007 compromise temporal 20 resolution vs. ambience stability and transient quality degradation vs. ambience decorrelation. A system utilizing the temporal permutation method, for example, will exhibit perceivable degradation of the 25 output sound due to a certain repetitive quality in the output audio signal. This is because of the fact that one and the same segment of the input signal appears unaltered in every output channel, though at a different point in time. Furthermore, to avoid increased applause density, 30 some original channels have to be dropped in the up-mix and, thus, some important auditory event might be missed in the resulting up-mix. In object-orientated systems, typically such sound events 35 are spatialized as a large group of point-like sources, which leads to a computationally complex implementation. 2936077_1 (GHMatters) P88385.AU - 7 Summary of the Invention According to a first broad aspect, the invention provides an apparatus for determining a spatial output multi channel audio signal based on an input audio signal, 5 comprising: a semantic decomposer configured for decomposing the input audio signal to obtain a first decomposed signal having a first semantic property, the first decomposed signal being a foreground signal part, and a second 10 decomposed signal having a second semantic property being different from the first semantic property, the second decomposed signal being a background signal part; and a renderer for rendering the first decomposed signal using a first rendering characteristic to obtain a first 15 rendered signal having the first semantic property and for rendering the second decomposed signal using a second rendering characteristic to obtain a second rendered signal having the second semantic property, wherein the first rendering characteristic and the second rendering 20 characteristic are different from each other; wherein the renderer comprises: a first DirAC monosynth stage for rendering the foreground signal part, the first DirAC monosynth stage being configured for creating a first mono-DirAC stream 25 leading to a perception of a nearby point-like source, and a second DirAC monosynth stage for rendering the background signal part, the second DirAC monosynth stage being configured for creating a mono-DirAC stream leading to a perception of spatially-spread sound, wherein each of 30 the mono-DirAC streams comprises omnidirectional signal data and directional data, the corresponding DirAC monosynth stage being configured for generating the respective directional data by controlling, in time or frequency, directional data input into the corresponding 35 DirAC monosynth stage; and a processor for processing the first rendered signal and the second rendered signal to obtain the spatial output multi-channel audio signal, wherein the processor comprises a DirAC merging stage for merging the 40 first mono-DirAC stream and the second mono-DirAC stream.

- 8 In one embodiment, the first DirAC monosynth stage is configured so that azimuth data is kept constant with frequency and changed randomly or controlled by an external process in time within a controlled azimuth 5 range, and a diffuseness parameter is set to zero, and the second DirAC monosynth stage is configured so that azimuth data are set random in time and frequency within given constraint azimuth values. 10 According to a second broad aspect, the invention provides a method for determining a spatial output multi-channel audio signal based on an input audio signal and an input parameter, the method comprising: semantically decomposing the input audio signal to 15 obtain a first decomposed signal having a first semantic property, the first decomposed signal being a foreground signal part, and a second decomposed signal having a second semantic property being different from the first semantic property, the second decomposed signal being a 20 background signal part; rendering the first decomposed signal using a first rendering characteristic to obtain a first rendered signal having the first semantic property by processing the first decomposed signal in a first DirAC monosynth stage, the 25 first DirAC monosynth stage being configured for creating a first mono-DirAC stream leading to a perception of a nearby point-like source; rendering the second decomposed signal using a second rendering characteristic to obtain a second rendered 30 signal having the second semantic property by processing the second decomposed signal in a second DirAC monosynth stage, the second DirAC monosynth stage being configured for creating a mono-DirAC stream leading to a perception of spatially-spread sound, wherein each of the mono-DirAC 35 streams comprises omnidirectional signal data and directional data, the corresponding DirAC monosynth stage being configured for generating the respective directional data by controlling, in time or frequency, directional data input into the corresponding DirAC monosynth stage; 40 and - 9 processing the first rendered signal and the second rendered signal to obtain the spatial output multi-channel audio signal by using a DirAC merging stage for merging the first mono-DirAC stream and the second mono-DirAC 5 stream. It is a finding of certain embodiments of the present invention that an audio signal can be decomposed in several components to which a spatial rendering, for 10 example, in terms of a decorrelation or in terms of an amplitude-panning approach, can be adapted. In other words, certain embodiments of the present invention are based on the finding that, for example, in a scenario with multiple audio sources, foreground and background sources 15 can be distinguished and rendered or decorrelated differently. Generally different spatial depths and/or extents of audio objects can be distinguished. One of the key points of certain embodiments is the 20 decomposition of signals, like the sound originating from an applauding audience, a flock of birds, a sea shore, galloping horses, a division of marching soldiers, etc. into a foreground and a background part, whereby the foreground part contains single auditory events originated 25 from, for example, nearby sources and the background part holds the ambience of the perceptually-fused far-off events. In such embodiments, prior to final mixing, these two signal parts are processed separately, for example, in order to synthesize the correlation, render a scene, etc. 30 Embodiments are not bound to distinguish only foreground and background parts of the signal, they may distinguish multiple different audio parts, which all may be rendered or decorrelated differently. 35 In general, audio signals may be decomposed into n different semantic parts by embodiments, which are processed separately. The decomposition/separate processing of different semantic components may be 40 accomplished in the time and/or in the frequency domain by embodiments.

- 10 Embodiments may provide the advantage of superior perceptual quality of the rendered sound at moderate computational cost. Embodiments therewith provide a novel decorrelation/rendering method that offers high perceptual 5 quality at moderate costs, especially for applause-like critical audio material or other similar ambience material like, for example, the noise that is emitted by a flock of birds, a sea shore, galloping horses, a division of marching soldiers, etc. 10 Brief Description of the Drawing In order that the invention may be more clearly ascertained, embodiments will now be described, by way of example, with reference to the accompanying drawing, in 15 which: Fig. la shows an embodiment of an apparatus for determining a spatial audio multi-channel audio signal; 20 Fig. lb shows a block diagram of another embodiment; Fig. 2 shows an embodiment illustrating a multiplicity of decomposed signals; 25 Fig. 3 illustrates an embodiment with a foreground and a background semantic decomposition; Fig. 4 illustrates an example of a transient separation 30 method for obtaining a background signal component; Fig. 5 illustrates a synthesis of sound sources having spatially a large extent; 35 2936077_1 (GHMalters) P88385.AU - 11 Fig. 6 illustrates one state of the art application of a decorrelator in time domain in a mono-to-stereo up-mixer; and 5 Fig. 7 shows another state of the art application of a decorrelator in frequency domain in a mono-to stereo up-mixer scenario. Detailed Description 10 Fig. 1 shows an embodiment of an apparatus 100 for determining a spatial output multi-channel audio signal based on an input audio signal. In some embodiments the apparatus can be adapted for further basing the spatial output multi-channel audio signal on an input parameter. 15 The input parameter may be generated locally or provided with the input audio signal, for example, as side information. In the embodiment depicted in Fig. 1, the apparatus 100 20 comprises a decomposer 110 for decomposing the input audio signal to obtain a first decomposed signal having a first semantic property and a second decomposed signal having a second semantic property being different from the first semantic property. 25 The apparatus 100 further comprises a renderer 120 for rendering the first decomposed signal using a first rendering characteristic to obtain a first rendered signal having the first semantic property and for rendering the 30 second decomposed signal using a second rendering characteristic to obtain a second rendered signal having the second semantic property. A semantic property may correspond to a spatial property, 35 as close or far, focused or wide, and/or a dynamic property as e.g. whether a signal is tonal, stationary or transient and/or a dominance property as e.g. whether the 2938077_1 (GHMatters) P88365.AU - 12 signal is foreground or background, a measure thereof respectively. Moreover, in the embodiment, the apparatus 100 comprises a 5 processor 130 for processing the first rendered signal and the second rendered signal to obtain the spatial output multi-channel audio signal. In other words, the decomposer 110 is adapted for 10 decomposing the input audio signal, in some embodiments based on the input parameter. The decomposition of the input audio signal is adapted to semantic , e.g. spatial, properties of different parts of the input audio signal. Moreover, rendering carried out by the renderer 120 15 according to the first and second rendering characteristics can also be adapted to the spatial properties, which allows, for example in a scenario where the first decomposed signal corresponds to a background audio signal and the second decomposed signal corresponds 20 to a foreground audio signal, different rendering or decorrelators may be applied, the other way around respectively. In the following the term "foreground" is understood to refer to an audio object being dominant in an audio environment, such that a potential listener would 25 notice a foreground-audio object. A foreground audio object or source may be distinguished or differentiated from a background audio object or source. A background audio object or source may not be noticeable by a potential listener in an audio environment as being less 30 dominant than a foreground audio object or source. In embodiments foreground audio objects or sources may be, but are not limited to, a point-like audio source, where background audio objects or sources may correspond to spatially wider audio objects or sources. 35 In other words, in embodiments the first rendering characteristic can be based on or matched to the first 27 On77 I (MHMatter P838S.AU - 13 semantic property and the second rendering characteristic can be based on or matched to the second semantic property. In one embodiment the first semantic property and the first rendering characteristic correspond to a 5 foreground audio source or object and the renderer 120 can be adapted to apply amplitude panning to the first decomposed signal. The renderer 120 may then be further adapted for providing as the first rendered signal two amplitude panned versions of the first decomposed signal. 10 In this embodiment, the second semantic property and the second rendering characteristic correspond to a background audio source or object, a plurality thereof respectively, and the renderer 120 can be adapted to apply a decorrelation to the second decomposed signal and provide 15 as second rendered signal the second decomposed signal and the decorrelated version thereof. In embodiments, the renderer 120 can be further adapted for rendering the first decomposed signal such that the 20 first rendering characteristic does not have a delay introducing characteristic. In other words, there may be no decorrelation of the first decomposed signal. In another embodiment, the first rendering characteristic may have a delay introducing characteristic having a first 25 delay amount and the second rendering characteristic may have a second delay amount, the second delay amount being greater than the first delay amount. In other words in this embodiment, both the first decomposed signal and the second decomposed signal may be decorrelated, however, the 30 level of decorrelation may scale with amount of delay introduced to the respective decorrelated versions of the decomposed signals. The decorrelation may therefore be stronger for the second decomposed signal than for the first decomposed signal. 35 In embodiments, the first decomposed signal and the second decomposed signal may overlap and/or may be time 2936077_1 (GHMatters) P88385 AU - 14 synchronous. In other words, signal processing may be carried out block-wise, where one block of input audio signal samples may be sub-divided by the decomposer 110 in a number of blocks of decomposed signals. In embodiments, 5 the number of decomposed signals may at least partly overlap in the time domain, i.e. they may represent overlapping time domain samples. In other words, the decomposed signals may correspond to parts of the input audio signal, which overlap, i.e. which represent at least 10 partly simultaneous audio signals. In embodiments the first and second decomposed signals may represent filtered or transformed versions of an original input signal. For example, they may represent signal parts being extracted from a composed spatial signal corresponding for example 15 to a close sound source or a more distant sound source. In other embodiments they may correspond to transient and stationary signal components, etc. In embodiments, the renderer 120 may be sub-divided in a 20 first renderer and a second renderer, where the first renderer can be adapted for rendering the first decomposed signal and the second renderer can be adapted for rendering the second decomposed signal. In embodiments, the renderer 120 may be implemented in software, for 25 example, as a program stored in a memory to be run on a processor or a digital signal processor which, in turn, is adapted for rendering the decomposed signals sequentially. The renderer 120 can be adapted for decorrelating the 30 first decomposed signal to obtain a first decorrelated signal and/or for decorrelating the second decomposed signal to obtain a second decorrelated signal. In other words, the renderer 120 may be adapted for decorrelating both decomposed signals, however, using different 35 decorrelation or rendering characteristics. In embodiments, the renderer 120 may be adapted for applying amplitude panning to either one of the first or second 2938077_1 (GHMatters) P86365.AU - 15 decomposed signals instead or in addition to decorrelation. The renderer 120 may be adapted for rendering the first 5 and second rendered signals each having as many components as channels in the spatial output multi-channel audio signal and the processor 130 may be adapted for combining the components of the first and second rendered signals to obtain the spatial output multi-channel audio signal. In 10 other embodiments the renderer 120 can be adapted for rendering the first and second rendered signals each having less components than the spatial output multi channel audio signal and wherein the processor 130 can be adapted for up-mixing the components of the first and 15 second rendered signals to obtain the spatial output multi-channel audio signal. Fig. lb shows another embodiment of an apparatus 100, comprising similar components as were introduced with the 20 help of Fig. la. However, Fig. lb shows an embodiment having more details. Fig. lb shows a decomposer 110 receiving the input audio signal and optionally the input parameter. As can be seen from Fig. lb, the decomposer is adapted for providing a first decomposed signal and a 25 second decomposed signal to a renderer 120, which is indicated by the dashed lines. In the embodiment shown in Fig. 1b, it is assumed that the first decomposed signal corresponds to a point-like audio source as the first semantic property and that the renderer 120 is adapted for 30 applying amplitude-panning as the first rendering characteristic to the first decomposed signal. In embodiments the first and second decomposed signals are exchangeable, i.e. in other embodiments amplitude-panning may be applied to the second decomposed signal. 35 In the embodiment depicted in Fig. 1b, the renderer 120 shows, in the signal path of the first decomposed signal, 2938077_1 (GHMatters) P86385.AU - 16 two scalable amplifiers 121 and 122, which are adapted for amplifying two copies of the first decomposed signal differently. The different amplification factors used may, in embodiments, be determined from the input parameter, in 5 other embodiments, they may be determined from the input audio signal, it may be preset or it may be locally generated, possibly also referring to a user input. The outputs of the two scalable amplifiers 121 and 122 are provided to the processor 130, for which details will be 10 provided below. As can be seen from Fig. 1b, the decomposer 110 provides a second decomposed signal to the renderer 120, which carries out a different rendering in the processing path 15 of the second decomposed signal. In other embodiments, the first decomposed signal may be processed in the presently described path as well or instead of the second decomposed signal. The first and second decomposed signals can be exchanged in embodiments. 20 In the embodiment depicted in Fig. 1b, in the processing path of the second decomposed signal, there is a decorrelator 123 followed by a rotator or parametric stereo or up-mix module 124 as second rendering 25 characteristic. The decorrelator 123 can be adapted for decorrelating the second decomposed signal X[k] and for providing a decorrelated version Q[k] of the second decomposed signal to the parametric stereo or up-mix module 124. In Fig. 1b, the mono signal X[k] is fed into 30 the decorrelator unit "D" 123 as well as the up-mix module 124. The decorrelator unit 123 may create the decorrelated version Q[k] of the input signal, having the same frequency characteristics and the same long term energy. The up-mix module 124 may calculate an up-mix matrix based on the 35 spatial parameters and synthesize the output channels Y[k] and Y 2 [k]. The up-mix module can be explained according to 2936077_1 (GHMatters) P88365.AU - 17 Y[k] c, 0][cos(a+fl) sin (a + f) X[k]~

Y

2 [k]j o c, cos(-a+p) sin(-a+l)j[ Q[ki_ with the parameters c,, c,, a and # being constants, or time- and frequency-variant values estimated from the 5 input signal X[k] adaptively, or transmitted as side information along with the input signal X[k] in the form of e.g. ILD (ILD = Inter channel Level Difference) parameters and ICC (ICC = Inter Channel Correlation) parameters. The signal X[k] is the received mono signal, 10 the signal Q[k] is the de-correlated signal, being a decorrelated version of the input signal X[k]. The output signals are denoted by Y[k] and Y2[k]. The decorrelator 123 may be implemented as an IIR filter 15 (IIR = Infinite Impulse Response), an arbitrary FIR filter (FIR = Finite Impulse response) or a special FIR filter using a single tap for simply delaying the signal. The parameters c,, c,., a and # can be determined in 20 different ways. In some embodiments, they are simply determined by input parameters, which can be provided along with the input audio signal, for example, with the down-mix data as a side information. In other embodiments, they may be generated locally or derived from properties 25 of the input audio signal. In the embodiment shown in Fig. lb, the renderer 120 is adapted for providing the second rendered signal in terms of the two output signals ;[k] and Y2[k] of the up-mix 30 module 124 to the processor 130. According to the processing path of the first decomposed signal, the two amplitude-panned versions of the first decomposed signal, available from the outputs of the two 35 scalable amplifiers 121 and 122 are also provided to the 2936077 1 (GHMatters) P88365.AU - 18 processor 130. In other embodiments, the scalable amplifiers 121 and 122 may be present in the processor 130, where only the first decomposed signal and a panning factor may be provided by the renderer 120. 5 As can be seen in Fig. 1b, the processor 130 can be adapted for processing or combining the first rendered signal and the second rendered signal, in this embodiment simply by combining the outputs in order to provide a 10 stereo signal having a left channel L and a right channel R corresponding to the spatial output multi-channel audio signal of Fig. la. In the embodiment in Fig. 1b, in both signaling paths, the 15 left and right channels for a stereo signal are determined. In the path of the first decomposed signal, amplitude panning is carried out by the two scalable amplifiers 121 and 122, therefore, the two components result in two in-phase audio signals, which are scaled 20 differently. This corresponds to an impression of a point like audio source as a semantic property or rendering characteristic. In the signal-processing path of the second decomposed 25 signal, the output signals Yk] and Y 2 [k] are provided to the processor 130 corresponding to left and right channels as determined by the up-mix module 124. The parameters c,, C,, a and 8 determine the spatial wideness of the corresponding audio source. In other words, the parameters 30 c,, c,., a and #8 can be chosen in a way or range such that for the L and R channels any correlation between a maximum correlation and a minimum correlation can be obtained in the second signal-processing path as second rendering characteristic. Moreover, this may be carried out 35 independently for different frequency bands. In other words, the parameters c,, cr, a and #8 can be chosen in a 29360771 (GHMatters) P80385 AU - 19 way or range such that the L and R channels are in-phase, modeling a point-like audio source as semantic property. The parameters c,, C,, a and 8 may also be chosen in a 5 way or range such that the L and R channels in the second signal processing path are decorrelated, modeling a spatially rather distributed audio source as semantic property, e.g. modeling a background or spatially wider sound source. 10 Fig. 2 illustrates another embodiment, which is more general. Fig. 2 shows a semantic decomposition block 210, which corresponds to the decomposer 110. The output of the semantic decomposition 210 is the input of a rendering 15 stage 220, which corresponds to the renderer 120. The rendering stage 220 is composed of a number of individual renderers 221 to 22n, i.e. the semantic decomposition stage 210 is adapted for decomposing a mono/stereo input signal into n decomposed signals, having n semantic 20 properties. The decomposition can be carried out based on decomposition controlling parameters, which can be provided along with the mono/stereo input signal, be preset, be generated locally or be input by a user, etc. 25 In other words, the decomposer 110 can be adapted for decomposing the input audio signal semantically based on the optional input parameter and/or for determining the input parameter from the input audio signal. 30 The output of the decorrelation or rendering stage 220 is then provided to an up-mix block 230, which determines a multi-channel output on the basis of the decorrelated or rendered signals and optionally based on up-mix controlled parameters. 35 Generally, embodiments may separate the sound material into n different semantic components and decorrelate each 2936077_1 (GHMatters) P88385.AU - 20 component separately with a matched decorrelator, which are also labeled D' to D" in Fig. 2. In other words, in embodiments the rendering characteristics can be matched to the semantic properties of the decomposed signals. 5 Each of the decorrelators or renderers can be adapted to the semantic properties of the accordingly-decomposed signal component. Subsequently, the processed components can be mixed to obtain the output multi-channel signal. The different components could, for example, correspond 10 foreground and background modeling objects. In other words, the renderer 110 can be adapted for combining the first decomposed signal and the first decorrelated signal to obtain a stereo or multi-channel 15 up-mix signal as the first rendered signal and/or for combining the second decomposed signal and the second decorrelated signal to obtain a stereo up-mix signal as the second rendered signal. 20 Moreover, the renderer 120 can be adapted for rendering the first decomposed signal according to a background audio characteristic and/or for rendering the second decomposed signal according to a foreground audio characteristic or vice versa. 25 Since, for example, applause-like signals can be seen as composed of single, distinct nearby claps and a noise-like ambience originating from very dense far-off claps, a suitable decomposition of such signals may be obtained by 30 distinguishing between isolated foreground clapping events as one component and noise-like background as the other component. In other words, in one embodiment, n=2. In such an embodiment, for example, the renderer 120 may be adapted for rendering the first decomposed signal by 35 amplitude panning of the first decomposed signal. In other words, the correlation or rendering of the foreground clap component may, in embodiments, be achieved in D' by 2938077_1 (GHMatters) P88385 AU - 21 amplitude panning of each single event to its estimated original location. In embodiments, the renderer 120 may be adapted for 5 rendering the first and/or second decomposed signal, for example, by all-pass filtering the first or second decomposed signal to obtain the first or second decorrelated signal. 10 In other words, in embodiments, the background can be decorrelated or rendered by the use of m mutually independent all-pass filters D ... m. In embodiments, only the quasi-stationary background may be processed by the all pass filters, the temporal smearing effects of the state 15 of the art decorrelation methods can be avoided this way. As amplitude panning may be applied to the events of the foreground object, the original foreground applause density can approximately be restored as opposed to the state of the art's system as, for example, presented in 20 paragraph J. Breebaart, S. van de Par, A. Kohlrausch, E. Schuijers, "High-Quality Parametric Spatial Audio Coding at Low Bitrates" in AES 116th Convention, Berlin, Preprint 6072, May 2004 and J. Herre, K. Kj6rling, J. Breebaart, et. al., "MPEG Surround - the ISO/MPEG Standard for 25 Efficient and Compatible Multi-Channel Audio Coding" in Proceedings of the 122nd AES Convention, Vienna, Austria, May 2007. In other words, in embodiments, the decomposer 110 can be 30 adapted for decomposing the input audio signal semantically based on the input parameter, wherein the input parameter may be provided along with the input audio signal as, for example, a side information. In such an embodiment, the decomposer 110 can be adapted for 35 determining the input parameter from the input audio signal. In other embodiments, the decomposer 110 can be adapted for determining the input parameter as a control 2938077_1 (GHMatters) P86385.AU - 22 parameter independent from the input audio signal, which may be generated locally, preset, or may also be input by a user. 5 In embodiments, the renderer 120 can be adapted for obtaining a spatial distribution of the first rendered signal or the second rendered signal by applying a broadband amplitude panning. In other words, according to the description of Fig. lb above, instead of generating a 10 point-like source, the panning location of the source can be temporally varied in order to generate an audio source having a certain spatial distribution. In embodiments, the renderer 120 can be adapted for applying the locally generated low-pass noise for amplitude panning, i.e. the 15 scaling factors for the amplitude panning for, for example, the scalable amplifiers 121 and 122 in Fig. lb correspond to a locally-generated noise value, i.e. are time-varying with a certain bandwidth. 20 Embodiments may be adapted for being operated in a guided or an unguided mode. For example, in a guided scenario, referring to the dashed lines, for example in Fig. 2, the decorrelation can be accomplished by applying standard technology decorrelation filters controlled on a coarse 25 time grid to, for example, the background or ambience part only and obtain the correlation by redistribution of each single event in, for example, the foreground part via time variant spatial positioning using broadband amplitude panning on a much finer time grid. In other words, in 30 embodiments, the renderer 120 can be adapted for operating decorrelators for different decomposed signals on different time grids, e.g. based on different time scales, which may be in terms of different sample rates or different delay for the respective decorrelators. In one 35 embodiment, carrying out foreground and background separation, the foreground part may use amplitude panning, where the amplitude is changed on a much finer time grid 29380771 (GHMatters) P88385.AU - 23 than operation for a decorrelator with respect to the background part. Furthermore, it is emphasized that for the decorrelation 5 of, for example, applause-like signals, i.e. signals with quasi-stationary random quality, the exact spatial position of each single foreground clap may not be as much of crucial importance, as rather the recovery of the overall distribution of the multitude of clapping events. 10 Embodiments may take advantage of this fact and may operate in an unguided mode. In such a mode, the aforementioned amplitude-panning factor could be controlled by low-pass noise. Fig. 3 illustrates a mono to-stereo system implementing the scenario. Fig. 3 shows a 15 semantic decomposition block 310 corresponding to the decomposer 110 for decomposing the mono input signal into a foreground and background decomposed signal part. As can be seen from Fig. 3, the background decomposed part 20 of the signal is rendered by all-pass D' 320. The decorrelated signal is then provided together with the un rendered background decomposed part to the up-mix 330, corresponding to the processor 130. The foreground decomposed signal part is provided to an amplitude panning 25 D2 stage 340, which corresponds to the renderer 120. Locally-generated low-pass noise 350 is also provided to the amplitude panning stage 340, which can then provide the foreground-decomposed signal in an amplitude-panned configuration to the up-mix 330. The amplitude panning D 2 30 stage 340 may determine its output by providing a scaling factor k for an amplitude selection between two of a stereo set of audio channels. The scaling factor k may be based on the lowpass noise. 35 As can be seen from Fig. 3, there is only one arrow between the amplitude panning 340 and the up-mix 330. This one arrow may as well represent amplitude-panned signals, 2935077_1 (GHMatters) P88365.AU - 24 i.e. in case of stereo up-mix, already the left and the right channel. As can be seen from Fig. 3, the up-mix 330 corresponding to the processor 130 is then adapted to process or combine the background and foreground 5 decomposed signals to derive the stereo output. Other embodiments may use native processing in order to derive background and foreground decomposed signals or input parameters for decomposition. The decomposer 110 may 10 be adapted for determining the first decomposed signal and/or the second decomposed signal based on a transient separation method. In other words, the decomposer 110 can be adapted for determining the first or second decomposed signal based on a separation method and the other 15 decomposed signal based on the difference between the first determined decomposed signal and the input audio signal. In other embodiments, the first or second decomposed signal may be determined based on the transient separation method and the other decomposed signal may be 20 based on the difference between the first or second decomposed signal and the input audio signal. The decomposer 110 and/or the renderer 120 and/or the processor 130 may comprise a DirAC monosynth stage and/or 25 a DirAC synthesis stage and/or a DirAC merging stage. In embodiments the decomposer 110 can be adapted for decomposing the input audio signal, the renderer 120 can be adapted for rendering the first and/or second decomposed signals, and/or the processor 130 can be 30 adapted for processing the first and/or second rendered signals in terms of different frequency bands. Embodiments may use the following approximation for applause-like signals. While the foreground components can 35 be obtained by transient detection or separation methods, cf. Pulkki, Ville; "Spatial Sound Reproduction with Directional Audio Coding" in J. Audio Eng. Soc., Vol. 55, 2938077_1 (GHMatters) P88365 AU - 25 No. 6, 2007, the background component may be given by the residual signal. Fig. 4 depicts an example where a suitable method to obtain a background component x'(n) of, for example, an applause-like signal x(n) to implement the 5 semantic decomposition 310 in Fig. 3, i.e. an embodiment of the decomposer 120. Fig. 4 shows a time-discrete input signal x(n), which is input to a DFT 410 (DFT = Discrete Fourier Transform). The output of the DFT block 410 is provided to a block for smoothing the spectrum 420 and to 10 a spectral whitening block 430 for spectral whitening on the basis of the output of the DFT 410 and the output of the smooth spectrum stage 430. The output of the spectral whitening stage 430 is then 15 provided to a spectral peak-picking stage 440, which separates the spectrum and provides two outputs, i.e. a noise and transient residual signal and a tonal signal. The noise and transient residual signal is provided to an LPC filter 450 (LPC = Linear Prediction Coding) of which 20 the residual noise signal is provided to the mixing stage 460 together with the tonal signal as output of the spectral peak-picking stage 440. The output of the mixing stage 460 is then provided to a spectral shaping stage 470, which shapes the spectrum on the basis of the 25 smoothed spectrum provided by the smoothed spectrum stage 420. The output of the spectral shaping stage 470 is then provided to the synthesis filter 480, i.e. an inverse discrete Fourier transform in order to obtain x' (n) representing the background component. The foreground 30 component can then be derived as the difference between the input signal and the output signal, i.e. as x(n) x' (n). Embodiments of the present invention may be operated in a 35 virtual reality applications as, for example, 3D gaming. In such applications, the synthesis of sound sources with a large spatial extent may be complicated and complex when 2938077_1 (GHMatlers) P86385.AU - 26 based on conventional concepts. Such sources might, for example, be a seashore, a bird flock, galloping horses, the division of marching soldiers, or an applauding audience. Typically, such sound events are spatialized as 5 a large group of point-like sources, which leads to computationally-complex implementations, cf. Wagner, Andreas; Walther, Andreas; Melchoir, Frank; Straug, Michael; "Generation of Highly Immersive Atmospheres for Wave Field Synthesis Reproduction" at 1 1 6 th International 10 EAS Convention, Berlin, 2004. Embodiments may carry out a method, which performs the synthesis of the extent of sound sources plausibly but, at the same time, having a lower structural and computational 15 complexity. Embodiments may be based on DirAC (DirAC = Directional Audio Coding), cf. Pulkki, Ville; "Spatial Sound Reproduction with Directional Audio Coding" in J. Audio Eng. Soc., Vol. 55, No. 6, 2007. In other words, in embodiments, the decomposer 110 and/or the renderer 120 20 and/or the processor 130 may be adapted for processing DirAC signals. In other words, the decomposer 110 may comprise DirAC monosynth stages, the renderer 120 may comprise a DirAC synthesis stage and/or the processor may comprise a DirAC merging stage. 25 Embodiments may be based on DirAC processing, for example, using only two synthesis structures, for example, one for foreground sound sources and one for background sound sources. The foreground sound may be applied to a single 30 DirAC stream with controlled directional data, resulting in the perception of nearby point-like sources. The background sound may also be reproduced by using a single direct stream with differently-controlled directional data, which leads to the perception of spatially-spread 35 sound objects. The two DirAC streams may then be merged and decoded for arbitrary loudspeaker set-up or for headphones, for example. 2936077_1 (GHMatters) P88385 AU - 27 Fig. 5 illustrates a synthesis of sound sources having a spatially-large extent. Fig. 5 shows an upper monosynth block 610, which creates a mono-DirAC stream leading to a 5 perception of a nearby point-like sound source, such as the nearest clappers of an audience. The lower monosynth block 620 is used to create a mono-DirAC stream leading to the perception of spatially-spread sound, which is, for example, suitable to generate background sound as the 10 clapping sound from the audience. The outputs of the two DirAC monosynth blocks 610 and 620 are then merged in the DirAC merge stage 630. Fig. 5 shows that only two DirAC synthesis blocks 610 and 620 are used in this embodiment. One of them is used to create the sound events, which are 15 in the foreground, such as closest or nearby birds or closest or nearby persons in an applauding audience and the other generates a background sound, the continuous bird flock sound, etc. 20 The foreground sound is converted into a mono-DirAC stream with DirAC-monosynth block 610 in a way that the azimuth data is kept constant with frequency, however, changed randomly or controlled by an external process in time. The diffuseness parameter y is set to 0, i.e. representing a 25 point-like source. The audio input to the block 610 is assumed to be temporarily non-overlapping sounds, such as distinct bird calls or hand claps, which generate the perception of nearby sound sources, such as birds or clapping persons. The spatial extent of the foreground 30 sound events is controlled by adjusting the 0 and Grangeforeground, which means that individual sound events will be perceived in O±Orangeforeground directions, however, a single event may be perceived point-like. In other words, point-like sound sources are generated where the possible 35 positions of the point are limited to the range E ± E range-f oreground 2935077 1 (GHMatters) P86385 AU - 28 The background block 620 takes as input audio stream, a signal, which contains all other sound events not present in the foreground audio stream, which is intended to include lots of temporarily overlapping sound events, for 5 example hundreds of birds or a great number of far-away clappers. The attached azimuth values are then set random both in time and frequency, within given constraint azimuth values e±erangebackground. The spatial extent of the background sounds can thus be synthesized with low 10 computational complexity. The diffuseness y may also be controlled. If it was added, the DirAC decoder would apply the sound to all directions, which can be used when the sound source surrounds the listener totally. If it does not surround, diffuseness may be kept low or close to 15 zero, or zero in embodiments. Embodiments of the present invention can provide the advantage that superior perceptual quality of rendered sounds can be achieved at moderate computational cost. 20 Embodiments may enable a modular implementation of spatial sound rendering as, for example, shown in Fig. 5. Depending on certain implementation requirements of the inventive methods, the inventive methods can be 25 implemented in hardware or in software. The implementation can be performed using a digital storage medium and, particularly, a flash memory, a disc, a DVD or a CD having electronically-readable control signals stored thereon, which co-operate with the programmable computer system, 30 such that the inventive methods are performed. Generally, the present invention is, therefore, a computer-program product with a program code stored on a machine-readable carrier, the program code being operative for performing the inventive methods when the computer program product 35 runs on a computer. In other words, the inventive methods are, therefore, a computer program having a program code 29380771 (GHMatters) P88385 AU - 29 for performing at least one of the inventive methods when the computer program runs on a computer. In the claims that follow and in the preceding description 5 of the invention, except where the context requires otherwise owing to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, that is, to specify the presence of the stated features 10 but not to preclude the presence or addition of further features in various embodiments of the invention. Further, any reference herein to prior art is not intended to imply that such prior art forms or formed a part of the 15 common general knowledge in Australia or any other country. 2936077_ (GHMatters) P8836S.AU

Claims (8)

1. An apparatus for determining a spatial output multi channel audio signal based on an input audio signal, 5 comprising: a semantic decomposer configured for decomposing the input audio signal to obtain a first decomposed signal having a first semantic property, the first decomposed signal being a foreground signal part, and a second 10 decomposed signal having a second semantic property being different from the first semantic property, the second decomposed signal being a background signal part; and a renderer for rendering the first decomposed signal using a first rendering characteristic to obtain a first 15 rendered signal having the first semantic property and for rendering the second decomposed signal using a second rendering characteristic to obtain a second rendered signal having the second semantic property, wherein the first rendering characteristic and the second rendering 20 characteristic are different from each other; wherein the renderer comprises: a first DirAC monosynth stage for rendering the foreground signal part, the first DirAC monosynth stage being configured for creating a first mono-DirAC stream 25 leading to a perception of a nearby point-like source, and a second DirAC monosynth stage for rendering the background signal part, the second DirAC monosynth stage being configured for creating a mono-DirAC stream leading to a perception of spatially-spread sound, wherein each of 30 the mono-DirAC streams comprises omnidirectional signal data and directional data, the corresponding DirAC monosynth stage being configured for generating the respective directional data by controlling, in time or frequency, directional data input into the corresponding 35 DirAC monosynth stage; and a processor for processing the first rendered signal and the second rendered signal to obtain the spatial output multi-channel audio signal, wherein the processor comprises a DirAC merging stage for merging the 5252596_1 (GHMatters) P86385.AU.1 - 31 first mono-DirAC stream and the second mono-DirAC stream.

2. An apparatus as claimed in claim 1, wherein the first DirAC monosynth stage is configured so that azimuth data 5 is kept constant with frequency and changed randomly or controlled by an external process in time within a controlled azimuth range, and a diffuseness parameter is set to zero, and the second DirAC monosynth stage is configured so 10 that azimuth data are set random in time and frequency within given constraint azimuth values.

3. A method for determining a spatial output multi channel audio signal based on an input audio signal and an 15 input parameter, the method comprising: semantically decomposing the input audio signal to obtain a first decomposed signal having a first semantic property, the first decomposed signal being a foreground signal part, and a second decomposed signal having a 20 second semantic property being different from the first semantic property, the second decomposed signal being a background signal part; rendering the first decomposed signal using a first rendering characteristic to obtain a first rendered signal 25 having the first semantic property by processing the first decomposed signal in a first DirAC monosynth stage, the first DirAC monosynth stage being configured for creating a first mono-DirAC stream leading to a perception of a nearby point-like source; 30 rendering the second decomposed signal using a second rendering characteristic to obtain a second rendered signal having the second semantic property by processing the second decomposed signal in a second DirAC monosynth stage, the second DirAC monosynth stage being configured 35 for creating a mono-DirAC stream leading to a perception of spatially-spread sound, wherein each of the mono-DirAC streams comprises omnidirectional signal data and directional data, the corresponding DirAC monosynth stage being configured for generating the respective directional 5252590 1 (GHMatters) P88385.AU.1 - 32 data by controlling, in time or frequency, directional data input into the corresponding DirAC monosynth stage; and processing the first rendered signal and the second 5 rendered signal to obtain the spatial output multi-channel audio signal by using a DirAC merging stage for merging the first mono-DirAC stream and the second mono-DirAC stream. 10

4. A method as claimed in claim 3, wherein: in the first DirAC monosynth stage, azimuth data is kept constant with frequency and changed randomly or controlled by an external process in time within a controlled azimuth range, and a diffuseness parameter is 15 set to zero, and in the second DirAC monosynth stage, azimuth data is set random in time and frequency within given constraint azimuth values. 20

5. A computer program having program code for performing the method of either claim 3 or 4, when the program code runs on a computer or a processor.

6. An apparatus for determining a spatial output multi 25 channel audio signal based on an input audio signal, substantially as herein described with reference to any one of figures 1 to 5 of the accompanying drawings.

7. A method for determining a spatial output multi 30 channel audio signal based on an input audio signal and an input parameter, substantially as herein described with reference to any one of figures 1 to 5 of the accompanying drawings. 35

8. A computer program having program code for performing a method for determining a spatial output multi-channel audio signal based on an input audio signal and an input parameter, substantially as herein described with reference to any one of figures 1 to 5 of the accompanying 40 drawings. -- - HMI ItrM. u PRSA; AU I