Description

Technical Field

Embodiments according to the invention are related to a multi-channel decorrelator for providing a plurality of decorrelated signals on the basis of a plurality of decorrelator input signals.

Further embodiments according to the invention are related to a multi-channel audio decoder for providing at least two output audio signals on the basis of an encoded representation.

Further embodiments according to the invention are related to a multi-channel audio encoder for providing an encoded representation on the basis of at least two input audio signals.

Further embodiments according to the invention are related to a method for providing a plurality of decorrelated signals on the basis of a plurality of decorrelator input signals.

Some embodiments according to the invention are related to a method for providing at least two output audio signals on the basis of an encoded representation.

Some embodiments according to the invention are related to a method for providing an encoded representation on the basis of at least two input audio signals.

Some embodiments according to the invention are related to a computer program for performing one of said methods.

Some embodiments according to the invention are related to an encoded audio representation.

Generally speaking, some embodiments according to the invention are related to a decorrelation concept for multi-channel downmix/upmix parametric audio object coding systems.

Background of the Invention

In recent years, demand for storage and transmission of audio contents has steadily increased. Moreover, the quality requirements for the storage and transmission of audio contents have also steadily increased. Accordingly, the concepts for the encoding and decoding of audio content have been enhanced.

For example, the so called "Advanced Audio Coding" (AAC) has been developed, which is described, for example, in the international standard ISO/IEC 13818-7:2003. Moreover, some spatial extensions have been created, like for example the so called "MPEG Surround" concept, which is described, for example, in the international standard ISO/IEC 23003-1 :2007. Moreover, additional improvements for encoding and decoding of spatial information of audio signals are described in the international standard ISO/IEC 23003-2:2010, which relates to the so called "Spatial Audio Object Coding".

Moreover, a switchable audio encoding/decoding concept which provides the possibility to encode both general audio signals and speech signals with good coding efficiency and to handle multi-channel audio signals is defined in the international standard ISO/IEC 23003-3:2012, which describes the so called "Unified Speech and Audio Coding" concept.

Moreover, further conventional concepts are described in the references, which are mentioned at the end of the present description.

However, there is a desire to provide an even more advanced concept for an efficient coding and decoding of 3-dimensional audio scenes.

Summary of the Invention

An embodiment according to the invention creates a multi-channel decorrelator for providing a plurality of decorrelated signals on the basis of a plurality of decorrelator input signals. The multi-channel decorrelator is configured to premix a first set of N decorrelator input signals into a second set of K decorrelator input signals, wherein KK'.

This embodiment according to the invention is based on the idea that a complexity of the decorrelation can be reduced by premixing the first set of N decorrelator input signals into a second set of K decorrelator input signals, wherein the second set of K decorrelator input signals comprises less signals than the first set of N decorrelator input signals. Accordingly, the fundamental decorrelator functionality is performed on only K signals (the K decorrelator input signals of the second set) such that, for example, only K (individual) decorrelators (or individual decorrelations) are required (and not N decorrelators). Moreover, to provide N' decorrelator output signals, an upmix is performed, wherein the first set of K' decorrelator output signals is upmixed into the second set of N' decorrelator output signals. Accordingly, it is possible to obtain a comparatively large number of decorrelated signals (namely, N' signals of the second set of decorrelator output signals) on the basis of a comparatively large number of decorrelator input signals (namely, N signals of the first set of decorrelator input signals), wherein a core decorrelation functionality is performed on the basis of only K signals (for example using only K individual decorrelators). Thus, a significant gain in decorrelation efficiency is achieved, which helps to save processing power and resources (for example, energy).

In a preferred embodiment, the number K of signals of the second set of decorrelator input signals is equal to the number K' of signals of the first set of decorrelator output signals. Accordingly, there may for example be K individual decorrelators, each of which receives one decorrelator input signal (of the second set of decorrelator input signals) from the premixing, and each of which provides one decorrelator output signals (of the first set of decorrelator output signals) to the upmixing. Thus, simple individual decorrelators can be used, each of which provides one output signal on the basis of one input signal.

In another preferred embodiment, number N of signals of the first set of decorrelator input signals may be equal to the number N' of signals of the second set of decorrelator output signals. Thus, the number of signals received by the multi-channel decorrelator is equal to the number of signals provided by the multi-channel decorrelator, such that the multichannel decorrelator appears, from outside, like a bank of N independent decorrelators (wherein, however, the decorrelation result may comprise some imperfections due to the usage of only K input signals for the core decorrelator). Accordingly, the multi-channel decorrelator may be used as drop-in replacement for conventional decorrelators having an equal number of input signals and output signals. Moreover, it should be noted that the upmixing may, for example, be derived from the premixing in such a configuration with moderate effort.

In a preferred embodiment, the number N of signals of the first set of decorrelator input signals may be larger than or equal to 3, and the number N' of signals of the second set of decorrelator output signals may also be larger than or equal to 3. In such a case, the multi-channel decorrelator may provide particular efficiency.

In a preferred embodiment, the multi-channel decorrelator may be configured to premix the first set of N decorrelator input signals into a second set of K decorrelator input signals using a premixing matrix (i.e., using a linear premixing functionality). In this case, the multi-channel decorrelator may be configured to obtain the first set of K' decorrelator output signals on the basis of the second set of K decorrelator input signals (for example, using individual decorrelators). The multi-channel decorrelator may also be configured to upmix the first set of K' decorrelator output signals into the second set of N' decorrelator output signals using a postmixing matrix, i.e., using a linear postmixing function. Accordingly, distortions may be kept small. Also, the premixing and post mixing (also designated as upmixing) may be performed in a computationally efficient manner.

In a preferred embodiment, the multi-channel decorrelator may be configured to select the premixing matrix in dependence on spatial positions to which the channel signals of the first set of N decorrelator input signals are associated. Accordingly, spatial dependencies (or correlations) may be considered in the premixing process, which is helpful to avoid an excessive degradation due to the premixing process performed in the multi-channel decorrelator.

In a preferred embodiment, the multi-channel decorrelator may be configured to select the premixing matrix in dependence on correlation characteristics or covariance characteristics of the channel signals of the first set of N decorrelator input signals. Such a functionality may also help to avoid excessive distortions due to the premixing performed by the multi-channel decorrelator. For example, decorrelator input signals (of the first set of decorrelator input signals), which are closely related (i.e., comprise a high cross-correlation or a high cross-covariance) may, for example, be combined into a single decorrelator input signal of the second set of decorrelator input signals, and may consequently be processed, for example, by a common individual decorrelator (of the decorrelator core). Thus, it can be avoided that substantially different decorrelator input signals (of the first set of decorrelator input signals) are premixed (or downmixed) into a single decorrelator input signal (of the second set of decorrelator input signals), which is input into the decorrelator core, since this will typically result in inappropriate decorrelator output signals (which would, for example, disturb a spatial perception when used to bring audio signals to desired cross-correlation characteristics or cross-covariance characteristics). Accordingly, the multi-channel decorrelator may decide, in an intelligent manner, which signals should be combined in the premixing (or downmixing) process to allow for a good compromise between decorrelation efficiency and audio quality.

In a preferred embodiment, the multi-channel decorrelator is configured to determine the premixing matrix such that a matrix-product between the premixing matrix and a Hermitian thereof is well-conditioned with respect to an inversion operation. Accordingly, the premixing matrix can be chosen such that a postmixing matrix can be determined without numerical problems.

In a preferred embodiment, the multi-channel decorrelator is configured to obtain the postmixing matrix on the basis of the premixing matrix using some matrix multiplication and matrix inversion operations. In this way, the postmixing matrix can be obtained efficiently, such that the postmixing matrix is well-adapted to the premixing process.

In a preferred embodiment, the multi-channel decorrelator is configured to receive an information about a rendering configuration associated with the channel signals of the first set of N decorrelator input signals. In this case, the multi-channel decorrelator is configured to select a premixing matrix in dependence on the information about the rendering configuration. Accordingly, the premixing matrix may be selected in a manner which is well-adapted to the rendering configuration, such that a good audio quality can be obtained.

In a preferred embodiment, the multi-channel decorrelator is configured to combine channel signals of the first set of N decorrelator input signals which are associated with spatially adjacent positions of an audio scene when performing the premixing. Thus, the fact that channel signals associated with spatially adjacent positions of an audio scene are typically similar is exploited when setting up the premixing. Consequently, similar audio signals may be combined in the premixing and processed using the same individual decorrelator in the decorrelator core. Accordingly, inacceptable degradations of the audio content can be avoided.

In a preferred embodiment, the multi-channel decorrelator is configured to combine channel signals of the first set of N decorrelator input signals which are associated with vertically spatially adjacent positions of an audio scene when performing the premixing. This concept is based on the finding that audio signals from vertically spatially adjacent positions of the audio scene are typically similar. Moreover, the human perception is not particularly sensitive with respect to differences between signals associated with vertically spatially adjacent positions of the audio scene. Accordingly, it has been found that combining audio signals associated with vertically spatially adjacent positions of the audio scene does not result in a substantial degradation of a hearing impression obtained on the basis of the decorrelated audio signals.

In a preferred embodiment, the multi-channel decorrelator may be configured to combine channel signals of the first set of N decorrelator input signals which are associated with a horizontal pair of spatial positions comprising a left side position and a right side position. It has been found that channel signals which are associated with a horizontal pair of spatial positions comprising a left side position and a right side position are typically also somewhat related since channel signals associated with a horizontal pair of spatial positions are typically used to obtain a spatial impression. Accordingly, it has been found that it is a reasonable solution to combine channel signals associated with a horizontal pair of spatial positions, for example if it is not sufficient to combine channel signals associated with vertically spatially adjacent positions of the audio scene, because combining channel signals associated with a horizontal pair of spatial positions typically does not result in an excessive degradation of a hearing impression.

In a preferred embodiment, the multi-channel decorrelator is configured to combine at least four channel signals of the first set of N decorrelator input signals, wherein at least two of said at least four channel signals are associated with spatial positions on a left side of an audio scene, and wherein at least two of said at least four channel signals are associated with spatial positions on a right side of an audio scene. Accordingly, four or more channels signals are combined, such that an efficient decorrelation can be obtained without significantly comprising a hearing impression.

In a preferred embodiment, the at least two left-sided channel signals (i.e., channel signals associated with spatial positions on the left side of the audio scene) to be combined are associated with spatial positions which are symmetrical, with respect to a center plane of the audio scene, to the spatial positions associated with the at least two right-sided channel signals to be combined (i.e., channel signals associated with spatial positions on the right side of the audio scene). It has been found that a combination of channel signals associated with "symmetrical" spatial positions typically brings along good results, since signals associated with such "symmetrical" spatial positions are typically somewhat related, which is advantageous for performing the common (combined) decorrelation.

In a preferred embodiment, the multi-channel decorrelator is configured to receive a complexity information describing a number K of decorrelator input signals of the second set of decorrelator input signals. In this case, the multi-channel decorrelator may be configured to select a premixing matrix in dependence on the complexity information. Accordingly, the multi-channel decorrelator can be adapted flexibly to different complexity requirements. Thus, it is possible to vary a compromise between audio quality and complexity.

In a preferred embodiment, the multi-channel decorrelator is configured to gradually (for example, step-wisely) increase a number of decorrelator input signals of the first set of decorrelator input signals which are combined together to obtain the decorrelator input signals of the second set of decorrelator input signals with a decreasing value of the complexity information. Accordingly, it is possible to combine more and more decorrelator input signals of the first set of decorrelator input signals (for example, into a single decorrelator input signal of the second set of decorrelator input signals) if it is desired to decrease the complexity, which allows to vary the complexity with little effort.

In a preferred embodiment, the multi-channel decorrelator is configured to combine only channel signals of the first set of N decorrelator input signals which are associated with vertically spatially adjacent positions of an audio scene when performing the premixing for a first value of the complexity information. However, the multi-channel decorrelator may (also) be configured to combine at least two channel signals of the first set of N decorrelator input signals which are associated with vertically spatially adjacent positions on the left side of the audio scene and at least two channel signals of the first set of N decorrelator input signals which are associated with vertically spatially adjacent positions on the right side of the audio scene in order to obtain a given signal of the second set of decorrelator input signals when performing the premixing for a second value of the complexity information. In other words, for the first value of the complexity information, no combination of channel signals from different sides of the audio scene may be performed, which results in a particularly good quality of the audio signals (and of a hearing impression, which can be obtained on the basis of the decorrelated audio signals). In contrast, if a smaller complexity is required, a horizontal combination may also be performed in addition to the vertical combination. It has been found that this a reasonable concept for a step-wise adjustment of the complexity, wherein a somewhat higher degradation of a hearing impression is found for reduced complexity.

In a preferred embodiment, the multi-channel decorrelator is configured to combine at least four channel signals of the first set of N decorrelator input signals, wherein at least two of said at least four channel signals are associated with spatial positions on a left side of an audio scene, and wherein at least two of said at least four channel signals are associated with spatial positions on a right side of the audio scene when performing the premixing for a second value of the complexity information. This concept is based on the finding that a comparatively low computational complexity can be obtained by combining at least two channel signals associated with spatial positions on a left side of the audio scene and at least two channel signals associated with spatial positions on a right side of the audio scene, even if said channel signals are not vertically adjacent (or at least not perfectly vertically adjacent).

In a preferred embodiment, the multi-channel decorrelator is configured to combine at least two channel signals of the first set of N decorrelator input signals which are associated with vertically spatially adjacent positions on a left side of the audio scene, in order to obtain a first decorrelator input signal of the second set of decorrelator input signals, and to combine at least two channel signals of the first set of N decorrelator input signals which are associated with vertically spatially adjacent positions on a right side of the audio scene, in order to obtain a second decorrelator input signal of the second set of decorrelator input signals for a first value of the complexity information. Moreover, the multi-channel decorrelator is preferably configured to combine the at least two channel signals of the first set of N decorrelator input signals which are associated with vertically spatially adjacent positions on the left side of the audio scene and the at least two channel signals of the first set of N decorrelator input signals which are associated with vertically spatially adjacent positions on the right side of the audio scene, in order to obtain a decorrelator input signal of the second set of decorrelator input signals for a second value of the complexity information. In this case, a number of decorrelator input signals of the second set of decorrelator input signals is larger for the first value of the complexity information than for the second value of the complexity information. In other words, four channel signals, which are used to obtain two decorrelator input signals of the second set of decorrelator input signals for the first value of the complexity information may be used to obtain a single decorrelator input signal of the second set of decorrelator input signals for the second value of the complexity information. Thus, signals which serve as input signals for two individual decorrelators for the first value of the complexity information are combined to serve as input signals for a single individual decorrelator for the second value of the complexity information. Thus, an efficient reduction of the number of individual decorrelators (or of the number of decorrelator input signals of the second set of decorrelator input signals) can be obtained for a reduced value of the complexity information.

An embodiment according to the invention creates a multi-channel audio decoder for providing at least two output audio signals on the basis of an encoded representation. The multi-channel audio decoder comprises a multi-channel decorrelator, as discussed herein.

This embodiment is based on the finding that the multi-channel audio decorrelator is well-suited for application in a multi-channel audio decoder.

In a preferred embodiment, the multi-channel audio decoder is configured to render a plurality of decoded audio signals, which are obtained on the basis of the encoded representation, in dependence on one or more rendering parameters, to obtain a plurality of rendered audio signals. The multi-channel audio decoder is configured to derive one or more decorrelated audio signals from the rendered audio signals using the multi-channel decorrelator, wherein the rendered audio signals constitute the first set of decorrelator input signals, and wherein the second set of decorrelator output signals constitute the decorrelated audio signals. The multi-channel audio decoder is configured to combine the rendered audio signals, or a scaled version thereof, with the one or more decorrelated

audio signals (of the second set of decorrelator output signals), to obtain the output audio signals. This embodiment according to the invention is based on the finding that the multichannel decorrelator described herein is well-suited for a post-rendering processing, wherein a comparatively large number of rendered audio signals is input into the multi-channel decorrelator, and wherein a comparatively large number of decorrelated signals is then combined with the rendered audio signals. Moreover, it has been found that the imperfections caused by the usage of a comparatively small number of individual decorrelators (complexity reduction in the multi-channel decorrelator) typically does not result in a severe degradation of a quality of the output audio signals output by the multi-channel decoder.

In a preferred embodiment, the multi-channel audio decoder is configured to select a premixing matrix for usage by the multi-channel decorrelator in dependence on a control information included in the encoded representation. Accordingly, it is even possible for an audio encoder to control the quality of the decorrelation, such that the quality of the decorrelation can be well-adapted to the specific audio content, which brings along a good tradeoff between audio quality and decorrelation complexity.

In a preferred embodiment, the multi-channel audio decoder is configured to select a premixing matrix for usage by the multi-channel decorrelator in dependence on an output configuration describing an allocation of output audio signals with spatial positions of the audio scene. Accordingly, the multi-channel decorrelator can be adapted to the specific rendering scenario, which helps to avoid substantial degradation of the audio quality by the efficient decorrelation.

In a preferred embodiment, the multi-channel audio decoder is configured to select between three or more different premixing matrices for usage by the multi-channel decorrelator in dependence on a control information included in the encoded representation for a given output representation. In this case, each of the three or more different premixing matrices is associated with a different number of signals of the second set of K decorrelator input signals. Thus, the complexity of the decorrelation can be adjusted over a wide range.

In a preferred embodiment, the multi-channel audio decoder is configured to select a premixing matrix (Mpre) for usage by the multi-channel decorrelator in dependence on a

mixing matrix (Dconv, Drender) which is used by an format converter or renderer which receives the at least two output audio signals.

In another embodiment, the multi-channel audio decoder is configured to select the premixing matrix (Mpre) for usage by the multi-channel decorrelator to be equal to a mixing matrix (Dconv, Drender) which is used by a format converter or renderer which receives the at least two output audio signals.

An embodiment according to the invention creates a multi-channel audio encoder for providing an encoded representation on the basis of at least two input audio signals. The multi-channel audio encoder is configured to provide one or more downmix signals on the basis of the at least two input audio signals. The multi-channel audio encoder is also configured to provide one or more parameters describing a relationship between the at least two input audio signals. Moreover, the multi-channel audio encoder is configured to provide a decorrelation complexity parameter describing a complexity of a decorrelation to be used at the side of an audio decoder. Accordingly, the multi-channel audio encoder is able to control the multi-channel audio decoder described above, such that the complexity of the decorrelation can be adjusted to the requirements of the audio content which is encoded by the multi-channel audio encoder.

Another embodiment according to the invention creates a method for providing a plurality of decorrelated signals on the basis of a plurality of decorrelator input signals. The method comprises premixing a first set of N decorrelator input signals into a second set of K decorrelator input signals, wherein KK'. This method is based on the same ideas as the above described multi-channel decorrelator.

Another embodiment according to the invention creates a method for providing at least two output audio signals on the basis of an encoded representation. The method comprises providing a plurality of decorrelated signals on the basis of a plurality of decorrelator input signals, as described above. This method is based on the same findings as the multi-channel audio decoder mentioned above.

Another embodiment creates a method for providing an encoded representation on the basis of at least two input audio signals. The method comprises providing one or more downmix signals on the basis of the at least two input audio signals. The method also comprises providing one or more parameters describing a relationship between the at least two input audio signals. Further, the method comprises providing a decorrelation complexity parameter describing a complexity of a decorrelation to be used at the side of an audio decoder. This method is based on the same ideas as the above described audio encoder.

Furthermore, embodiments according to the invention create a computer program for performing said methods.

Another embodiment according to the invention creates an encoded audio representation. The encoded audio representation comprises an encoded representation of a downmix signal and an encoded representation of one or more parameters describing a relationship between the at least two input audio signals. Furthermore, the encoded audio representation comprises an encoded decorrelation method parameter describing which decorrelation mode out of a plurality of decorrelation modes should be used at the side of an audio decoder. Accordingly, the encoded audio representation allows to control the multi-channel decorrelator described above, as well as the multi-channel audio decoder described above.

Moreover, it should be noted that the methods described above can be supplemented by any of the features and functionality described with respect to the apparatuses as mentioned above.

Brief Description of the Figures

Embodiments according to the present invention will subsequently be described taking reference to the enclosed figures in which:

Fig. 1 shows a block schematic diagram of a multi-channel audio decoder, according to an embodiment of the present invention;

Fig. 2 shows a block schematic diagram of a multi-channel audio encoder, according to an embodiment of the present invention;

shows a flowchart of a method for providing at least two output audio signals on the basis of an encoded representation, according to an embodiment of the invention;

shows a flowchart of a method for providing an encoded representation on the basis of at least two input audio signals, according to an embodiment of the present invention;

shows a schematic representation of an encoded audio representation, according to an embodiment of the present invention;

shows a block schematic diagram of a multi-channel decorrelator, according to an embodiment of the present invention;

shows a block schematic diagram of a multi-channel audio decoder, according to an embodiment of the present invention;

shows a block schematic diagram of a multi-channel audio encoder, according to an embodiment of the present invention,

shows a flowchart of a method for providing plurality of decorrelated signals on the basis of a plurality of decorrelator input signals, according to an embodiment of the present invention;

shows a flowchart of a method for providing at least two output audio signals on the basis of an encoded representation, according to an embodiment of the present invention;

shows a flowchart of a method for providing an encoded representation on the basis of at least two input audio signals, according to an embodiment of the present invention;

shows a schematic representation of an encoded representation, according to an embodiment of the present invention;

Fig. 13 shows schematic representation which provides an overview of an MMSE based parametric downmix/upmix concept;

Fig. 14 shows a geometric representation for an orthogonality principle in 3- dimensional space;

Fig. 15 shows a block schematic diagram of a parametric reconstruction system with decorrelation applied on rendered output, according to an embodiment of the present invention;

Fig. 16 shows a block schematic diagram of a decorrelation unit;

Fig. 17 shows a block schematic diagram of a reduced complexity decorrelation unit, according to an embodiment of the present invention;

Fig. 18 shows a table representation of loudspeaker positions, according to an embodiment of the present invention;

Figs. 19a to 19g show table representations of premixing coefficients for N = 22 and

K between 5 and 1 1 ;

Figs. 20a to 20d show table representations of premixing coefficients for N = 10 and

K between 2 and 5;

Figs. 21 a to 21 c show table representations of premixing coefficients for N = 8 and K between 2 and 4;

Figs 21 d to 21 f show table representations of premixing coefficients for N = 7 and K between 2 and 4;

Figs. 22a and 22b show table representations of premixing coefficients for N = 5 and

K = 2 or K = 3;

Fig. 23 shows a table representation of premixing coefficients for N = 2 and K =1 ;

Fig. 24 shows a table representation of groups of channel signals;

Fig. 25 shows a syntax representation of additional parameters, which may be included into the syntax of SAOCSpecifigConfigQ or, equivalently, SAOC3DSpecificConfig();

Fig. 26 shows a table representation of different values for the bitstream variable bsDecorrelationMethod;

Fig. 27 shows a table representation of a number of decorrelators for different decorrelation levels and output configurations, indicated by the bitstream variable bsDecorrelationLevel;

Fig. 28 shows, in the form of a block schematic diagram, an overview over a 3D audio encoder;

Fig. 29 shows, in the form of a block schematic diagram, an overview over a 3D audio decoder; and

Fig. 30 shows a block schematic diagram of a structure of a format converter.

Fig. 31 shows a block schematic diagram of a downmix processor, according to an embodiment of the present invention;

Fig. 32 shows a table representing decoding modes for different number of SAOC downmix objects; and

Fig. 33 shows a syntax representation of a bitstream element

"SAOC3DSpecificConfig".

Detailed Description of the Embodiments

1. Multi-channel audio decoder according to Fig. 1

Fig. 1 shows a block schematic diagram of a multi-channel audio decoder 100, according to an embodiment of the present invention.

The multi-channel audio decoder 100 is configured to receive an encoded representation 1 10 and to provide, on the basis thereof, at least two output audio signals 1 12, 1 14.

The multi-channel audio decoder 100 preferably comprises a decoder 120 which is configured to provide decoded audio signals 122 on the basis of the encoded representation 1 10. Moreover, the multi-channel audio decoder 100 comprises a renderer 30, which is configured to render a plurality of decoded audio signals 122, which are obtained on the basis of the encoded representation 1 10 (for example, by the decoder 120) in dependence on one or more rendering parameters 132, to obtain a plurality of rendered audio signals 134, 136. Moreover, the multi-channel audio decoder 100 comprises a decorrelator 140, which is configured to derive one or more decorrelated audio signals 142, 144 from the rendered audio signals 134, 136. Moreover, the multichannel audio decoder 100 comprises a combiner 150, which is configured to combine the rendered audio signals 134, 136, or a scaled version thereof, with the one or more decorrelated audio signals 142, 144 to obtain the output audio signals 1 12, 1 14.

However, it should be noted that a different hardware structure of the multi-channel audio decoder 100 may be possible, as long as the functionalities described above are given.

Regarding the functionality of the multi-channel audio decoder 100, it should be noted that the decorrelated audio signals 142, 144 are derived from the rendered audio signals 34, 136, and that the decorrelated audio signals 142, 144 are combined with the rendered audio signals 134, 136 to obtain the output audio signals 1 12, 1 14. By deriving the decorrelated audio signals 142, 144 from the rendered audio signals 134, 136, a particularly efficient processing can be achieved, since the number of rendered audio signals 134, 136 is typically independent from the number of decoded audio signals 122 which are input into the renderer 130. Thus, the decorrelation effort is typically independent from the number of decoded audio signals 122, which improves the implementation efficiency. Moreover, applying the decorrelation after the rendering avoids the introduction of artifacts, which could be caused by the renderer when combining multiple decorrelated signals in the case that the decorrelation is applied before the rendering. Moreover, characteristics of the rendered audio signals can be considered in the decorrelation performed by the decorrelator 140, which typically results in output audio signals of good quality.

Moreover, it should be noted that the multi-channel audio decoder 100 can be supplemented by any of the features and functionalities described herein. In particular, it should be noted that individual improvements as described herein may be introduced into the multi-channel audio decoder 100 in order to thereby even improve the efficiency of the processing and/or the quality of the output audio signals.

2. Multi-Channel Audio Encoder According to Fig. 2

Fig. 2 shows a block schematic diagram of a multi-channel audio encoder 200, according to an embodiment of the present invention. The multi-channel audio encoder 200 is configured to receive two or more input audio signals 210, 212, and to provide, on the basis thereof, an encoded representation 214. The multi-channel audio encoder comprises a downmix signal provider 220, which is configured to provide one or more downmix signals 222 on the basis of the at least two input audio signals 210, 212. Moreover, the multi-channel audio encoder 200 comprises a parameter provider 230, which is configured to provide one or more parameters 232 describing a relationship (for example, a cross-correlation, a cross-covariance, a level difference or the like) between the at least two input audio signals 210, 212.

Moreover, the multi-channel audio encoder 200 also comprises a decorrelation method parameter provider 240, which is configured to provide a decorrelation method parameter 242 describing which decorrelation mode out of a plurality of decorrelation modes should be used at the side of an audio decoder. The one or more downmix signals 222, the one or more parameters 232 and the decorrelation method parameter 242 are included, for example, in an encoded form, into the encoded representation 214.

However, it should be noted that the hardware structure of the multi-channel audio encoder 200 may be different, as long as the functionalities as described above are fulfilled. In other words, the distribution of the functionalities of the multi-channel audio encoder 200 to individual blocks (for example, to the downmix signal provider 220, to the parameter provider 230 and to the decorrelation method parameter provider 240) should only be considered as an example.

Regarding the functionality of the multi-channel audio encoder 200, it should be noted that the one or more downmix signals 222 and the one or more parameters 232 are provided in a conventional way, for example like in an SAOC multi-channel audio encoder or in a

USAC multi-channel audio encoder. However, the decorrelation method parameter 242, which is also provided by the multi-channel audio encoder 200 and included into the encoded representation 214, can be used to adapt a decorrelation mode to the input audio signals 210, 212 or to a desired playback quality. Accordingly, the decorrelation mode can be adapted to different types of audio content. For example, different decorrelation modes can be chosen for types of audio contents in which the input audio signals 210, 212 are strongly correlated and for types of audio content in which the input audio signals 210, 212 are independent. Moreover, different decorrelation modes can, for example, be signaled by the decorrelation mode parameter 242 for types of audio contents in which a spatial perception is particularly important and for types of audio content in which a spatial impression is less important or even of subordinate importance (for example, when compared to a reproduction of individual channels). Accordingly, a multi-channel audio decoder, which receives the encoded representation 214, can be controlled by the multi-channel audio encoder 200, and may be set to a decoding mode which brings along a best possible compromise between decoding complexity and reproduction quality.

Moreover, it should be noted that the multi-channel audio encoder 200 may be supplemented by any of the features and functionalities described herein. It should be noted that the possible additional features and improvements described herein may be added to the multi-channel audio encoder 200 individually or in combination, to thereby improve (or enhance) the multi-channel audio encoder 200.

3. Method for Providing at Least Two Output Audio Signals According to Fig. 3

Fig. 3 shows a flowchart of a method 300 for providing at least two output audio signals on the basis of an encoded representation. The method comprises rendering 310 a plurality of decoded audio signals, which are obtained on the basis of an encoded representation 312, in dependence on one or more rendering parameters, to obtain a plurality of rendered audio signals. The method 300 also comprises deriving 320 one or more decorrelated audio signals from the rendered audio signals. The method 300 also comprises combining 330 the rendered audio signals, or a scaled version thereof, with the one or more decorrelated audio signals, to obtain the output audio signals 332.

It should be noted that the method 300 is based on the same considerations as the multichannel audio decoder 100 according to Fig. 1 . Moreover, it should be noted that the method 300 may be supplemented by any of the features and functionalities described herein (either individually or in combination). For example, the method 300 may be supplemented by any of the features and functionalities described with respect to the multi-channel audio decoders described herein.

4. Method for Providing an Encoded Representation According to Fig. 4

Fig. 4 shows a flowchart of a method 400 for providing an encoded representation on the basis of at least two input audio signals. The method 400 comprises providing 410 one or more downmix signals on the basis of at least two input audio signals 412. The method 400 further comprises providing 420 one or more parameters describing a relationship between the at least two input audio signals 412 and providing 430 a decorrelation method parameter describing which decorrelation mode out of a plurality of decorrelation modes should be used at the side of an audio decoder. Accordingly, an encoded representation 432 is provided, which preferably includes an encoded representation of the one or more downmix signals, one or more parameters describing a relationship between the at least two input audio signals, and the decorrelation method parameter.

It should be noted that the method 400 is based on the same considerations as the multichannel audio encoder 200 according to Fig. 2, such that the above explanations also apply.

Moreover, it should be noted that the order of the steps 410, 420, 430 can be varied flexibly, and that the steps 410, 420, 430 may also be performed in parallel as far as this is possible in an execution environment for the method 400. Moreover, it should be noted that the method 400 can be supplemented by any of the features and functionalities described herein, either individually or in combination. For example, the method 400 may be supplemented by any of the features and functionalities described herein with respect to the multi-channel audio encoders. However, it is also possible to introduce features and functionalities which correspond to the features and functionalities of the multi-channel audio decoders described herein, which receive the encoded representation 432.

5. Encoded Audio Representation According to Fig. 5

Fig. 5 shows a schematic representation of an encoded audio representation 500 according to an embodiment of the present invention.

The encoded audio representation 500 comprises an encoded representation 510 of a downmix signal, an encoded representation 520 of one or more parameters describing a relationship between at least two audio signals. Moreover, the encoded audio representation 500 also comprises an encoded decorrelation method parameter 530 describing which decorrelation mode out of a plurality of decorrelation modes should be used at the side of an audio decoder. Accordingly, the encoded audio representation allows to signal a decorrelation mode from an audio encoder to an audio decoder. Accordingly, it is possible to obtain a decorrelation mode which is well-adapted to the characteristics of the audio content (which is described, for example, by the encoded representation 510 of one or more downmix signals and by the encoded representation 520 of one or more parameters describing a relationship between at least two audio signals (for example, the at least two audio signals which have been downmixed into the encoded representation 510 of one or more downmix signals)). Thus, the encoded audio representation 500 allows for a rendering of an audio content represented by the encoded audio representation 500 with a particularly good auditory spatial impression and/or a particularly good tradeoff between auditory spatial impression and decoding complexity.

Moreover, it should be noted that the encoded representation 500 may be supplemented by any of the features and functionalities described with respect to the multi-channel audio encoders and the multi-channel audio decoders, either individually or in combination.

6. Multi-Channel Decorrelator According to Fig. 6

Fig. 6 shows a block schematic diagram of a multi-channel decorrelator 600, according to an embodiment of the present invention.

The multi-channel decorrelator 600 is configured to receive a first set of N decorrelator input signals 610a to 61 On and provide, on the basis thereof, a second set of N' decorrelator output signals 612a to 612n'. In other words, the multi-channel decorrelator 600 is configured for providing a plurality of (at least approximately) decorrelated signals 612a to 612n' on the basis of the decorrelator input signals 610a to 61 On.

The multi-channel decorrelator 600 comprises a premixer 620, which is configured to premix the first set of N decorrelator input signals 610a to 61 On into a second set of K decorrelator input signals 622a to 622k, wherein K is smaller than N (with K and N being integers). The multi-channel decorrelator 600 also comprises a decorrelation (or decorrelator core) 630, which is configured to provide a first set of K' decorrelator output signals 632a to 632k' on the basis of the second set of K decorrelator input signals 622a to 622k. Moreover, the multi-channel decorrelator comprises an postmixer 640, which is configured to upmix the first set of K' decorrelator output signals 632a to 632k' into a second set of N' decorrelator output signals 612a to 612n', wherein N' is larger than K' (with N' and K' being integers).

However, it should be noted that the given structure of the multi-channel decorrelator 600 should be considered as an example only, and that it is not necessary to subdivide the multi-channel decorrelator 600 into functional blocks (for example, into the premixer 620, the decorrelation or decorrelator core 630 and the postmixer 640) as long as the functionality described herein is provided.

Regarding the functionality of the multi-channel decorrelator 600, it should also be noted that the concept of performing a premixing, to derive the second set of K decorrelator input signals from the first set of N decorrelator input signals, and of performing the decorrelation on the basis of the (premixed or "downmixed") second set of K decorrelator input signals brings along a reduction of a complexity when compared to a concept in which the actual decorrelation is applied, for example, directly to N decorrelator input signals. Moreover, the second (upmixed) set of N' decorrelator output signals is obtained on the basis of the first (original) set of decorrelator output signals, which are the result of the actual decorrelation, on the basis of an postmixing, which may be performed by the upmixer 640. Thus, the multi-channel decorrelator 600 effectively (when seen from the outside) receives N decorrelator input signals and provides, on the basis thereof, N' decorrelator output signals, while the actual decorrelator core 630 only operates on a smaller number of signals (namely K downmixed decorrelator input signals 622a to 622k of the second set of K decorrelator input signals). Thus, the complexity of the multi-channel decorrelator 600 can be substantially reduced, when compared to conventional decorrelators, by performing a downmixing or "premixing" (which may preferably be a

linear premixing without any decorrelation functionality) at an input side of the decorrelation (or decorrelator core) 630 and by performing the upmixing or "postmixing" (for example, a linear upmixing without any additional decorrelation functionality) on the basis of the (original) output signals 632a to 632k' of the decorrelation (decorrelator core) 630.

Moreover, it should be noted that the multi-channel decorrelator 600 can be supplemented by any of the features and functionalities described herein with respect to the multichannel decorrelation and also with respect to the multi-channel audio decoders. It should be noted that the features described herein can be added to the multi-channel decorrelator 600 either individually or in combination, to thereby improve or enhance the multi-channel decorrelator 600.

It should be noted that a multi-channel decorrelator without complexity reduction can be derived from the above described multichannel decorrelator for K=N (and possibly K'=N' or even K=N=K'=N').

7. Multi-channel Audio Decoder According to Fig. 7

Fig. 7 shows a block schematic diagram of a multi-channel audio decoder 700, according to an embodiment of the invention.

The multi-channel audio decoder 700 is configured to receive an encoded representation 710 and to provide, on the basis of thereof, at least two output signals 712, 714. The multi-channel audio decoder 700 comprises a multi-channel decorrelator 720, which may be substantially identical to the multi-channel decorrelator 600 according to Fig. 6. Moreover, the multi-channel audio decoder 700 may comprise any of the features and functionalities of a multi-channel audio decoder which are known to the man skilled in the art or which are described herein with respect to other multi-channel audio decoders.

Moreover, it should be noted that the multi-channel audio decoder 700 comprises a particularly high efficiency when compared to conventional multi-channel audio decoders, since the multi-channel audio decoder 700 uses the high-efficiency multi-channel decorrelator 720.

8. Multi-Channel Audio Encoder According to Fig. 8

Fig. 8 shows a block schematic diagram of a multi-channel audio encoder 800 according to an embodiment of the present invention. The multi-channel audio encoder 800 is configured to receive at least two input audio signals 810, 812 and to provide, on the basis thereof, an encoded representation 814 of an audio content represented by the input audio signals 810, 812.

The multi-channel audio encoder 800 comprises a downmix signal provider 820, which is configured to provide one or more downmix signals 822 on the basis of the at least two input audio signals 810, 812. The multi-channel audio encoder 800 also comprises a parameter provider 830 which is configured to provide one or more parameters 832 (for example, cross-correlation parameters or cross-covariance parameters, or inter-object-correlation parameters and/or object level difference parameters) on the basis of the input audio signals 810,812. Moreover, the multi-channel audio encoder 800 comprises a decorrelation complexity parameter provider 840 which is configured to provide a decorrelation complexity parameter 842 describing a complexity of a decorrelation to be used at the side of an audio decoder (which receives the encoded representation 814). The one or more downmix signals 822, the one or more parameters 832 and the decorrelation complexity parameter 842 are included into the encoded representation 814, preferably in an encoded form.

However, it should be noted that the internal structure of the multi-channel audio encoder 800 (for example, the presence of the downmix signal provider 820, of the parameter provider 830 and of the decorrelation complexity parameter provider 840) should be considered as an example only. Different structures are possible as long as the functionality described herein is achieved.

Regarding the functionality of the multi-channel audio encoder 800, it should be noted that the multi-channel encoder provides an encoded representation 814, wherein the one or more downmix signals 822 and the one or more parameters 832 may be similar to, or equal to, downmix signals and parameters provided by conventional audio encoders (like, for example, conventional SAOC audio encoders or USAC audio encoders). However, the multi-channel audio encoder 800 is also configured to provide the decorrelation complexity parameter 842, which allows to determine a decorrelation complexity which is applied at the side of an audio decoder. Accordingly, the decorrelation complexity can be adapted to the audio content which is currently encoded. For example, it is possible to signal a desired decorrelation complexity, which corresponds to an achievable audio quality, in dependence on an encoder-sided knowledge about the characteristics of the input audio signals. For example, if it is found that spatial characteristics are important for an audio signal, a higher decorrelation complexity can be signaled, using the decorrelation complexity parameter 842, when compared to a case in which spatial characteristics are not so important. Alternatively, the usage of a high decorrelation complexity can be signaled using the decorrelation complexity parameter 842, if it is found that a passage of the audio content or the entire audio content is such that a high complexity decorrelation is required at a side of an audio decoder for other reasons.

To summarize, the multi-channel audio encoder 800 provides for the possibility to control a multi-channel audio decoder, to use a decorrelation complexity which is adapted to signal characteristics or desired playback characteristics which can be set by the multichannel audio encoder 800.

Moreover, it should be noted that the multi-channel audio encoder 800 may be supplemented by any of the features and functionalities described herein regarding a multi-channel audio encoder, either individually or in combination. For example, some or all of the features described herein with respect to multi-channel audio encoders can be added to the multi-channel audio encoder 800. Moreover, the multi-channel audio encoder 800 may be adapted for cooperation with the multi-channel audio decoders described herein.
Ciaims

A multi-channel decorrelator (140; 600; 1590; 1700) for providing a plurality of decorrelated signals (142, 144; 612a-612n'; 1592a-1592n; 1712a-1712n) on the basis of a plurality of decorrelator input signals (134,136; 610a-610n; 1582a-1582n; 1710a-1710n),

wherein the multi-channel decorrelator is configured to premix a first set (134, 136; 610a-610n; 1582a-1582n; 1710a-1710n; Z) of N decorrelator input signals into a second set (622a-622k; 1722a-1722k; Zmix) of K decorrelator input signals, wherein KK'.

The multi-channel decorrelator according to claim 1 , wherein K=K'.

The multi-channel decorrelator according to claim 1 or claim 2, wherein N=N'.

The multi-channel decorrelator according to one of claims 1 to 3, wherein N>=3 and N'>=3.

The multi-channel decorrelator according to one of claims 1 to 4, wherein the multichannel decorrelator is configured to premix the first set Z of N decorrelator input signals into the second set Zmjx of K decorrelator input signals using a premixing matrix Mpre according to

Zm,v = MpreZ

wherein the multi-channel decorrelator is configured to obtain the first set ¾' of K' decorrelator output signals on the basis of the second set Zmix of K decorrelator input signals, and

wherein the multi-channel decorrelator is configured to upmix the first set ¾^ of K' decorrelator output signals into the second set W of N' decorrelator output signals using a postmixing matrix Mpost according to

6. The multi-channel decorrelator according to claim 5, wherein the multi-channel decorrelator is configured to select the premixing matrix Mpre in dependence on spatial positions to which the channel signals of the first set Z of N decorrelator input signals are associated.

7. The multi-channel decorrelator according to claim 5 or claim 6, wherein the multi- channel decorrelator is configured to select the premixing matrix Mpre in dependence on correlation characteristics or covariance characteristics of the channel signals of the first set Z of N decorrelator input signals.

8. The multi-channel decorrelator according to one of claims 5 to 7, wherein the multichannel decorrelator is configured to determine the pre-mixing matrix such that a matrix-product

( ^,Μ^.)

is well-conditioned with respect to an inversion operation.

9. The multi-channel decorrelator according to one of claims 5 to 8,

wherein the multi-channel decorrelator is configured to obtain the postmixing matrix post according to

M post Mpre MpTeM„re

The multi-channel decorrelator according to one of claims 1 to 9, wherein the multichannel decorrelator is configured to receive an information about a rendering configuration associated with the channel signals of the first set (Z) of N decorrelator input signals, and wherein the multi-channel decorrelator is configured to select a premixing matrix (Mpre) in dependence on the information about the rendering configuration.

The multi-channel decorrelator according to one of claims 1 to 10, wherein the multi-channel decorrelator is configured to combine channel signals of the first set (Z) of N decorrelator input signals which are associated with spatially adjacent positions of an audio scene when performing the premixing.

The multi-channel decorrelator according to claim 1 1 , wherein the multi-channel decorrelator is configured to combine channel signals of the first set (Z) of N decorrelator input signals which are associated with vertically spatially adjacent positions of the audio scene when performing the premixing.

The multi-channel decorrelator according to one of claims 1 to 12, wherein the multi-channel decorrelator is configured to combine channel signals of the first set (Z) of N decorrelator input signals which are associated with a horizontal pair of spatial positions comprising a left side position and a right side position.

The multi-channel decorrelator according to one of claims 1 to 13, wherein the multi-channel decorrelator is configured to combine at least four channel signals of the first set (Z) of N decorrelator input signals, wherein at least two of said at least four channel signals are associated with spatial positions on a left side of an audio scene, and wherein at least two of said at least four channel signals are associated with spatial positions on a right side of the audio scene.

The multi-channel decorrelator according claim 14, wherein the at least two left-sided channel signals to be combined are associated with spatial positions which are symmetrical, with respect to a center plane of the audio scene, to the spatial positions associated with the at least two right-sided channel signals to be combined.

The multi-channel decorrelator according to one of claims 1 to 15, wherein the multi-channel decorrelator is configured to receive a complexity information describing a number K of decorrelator input signals of the second set of decorrelator input signals, and wherein the multi-channel decorrelator is configured to select a premixing matrix (Mpre) in dependence on the complexity information.

The multi-channel decorrelator according to claim 16, wherein the multi-channel decorrelator is configured to step-wisely increase a number of decorrelator input signals of the first set (Z) of decorrelator input signals which are combined to obtain the decorrelator input signals of the second set of decorrelator input signals with a decreasing value of the complexity information.

The multi-channel decorrelator according to claim 16 or 17, wherein the multichannel decorrelator is configured to combine only channel signals of the first set (Z) of N decorrelator input signals which are associated with vertically spatially adjacent positions of an audio scene when performing the premixing for a first value of the complexity information, and

wherein the multi-channel decorrelator is configured to combine at least two channel signals of the first set ( ) of N decorrelator input signals which are associated with vertically spatially adjacent positions on a left side of the audio scene and at least two channel signals of the first set (Z) of N decorrelator input signals which are associated with vertically spatially adjacent positions on a right side of the audio scene in order to obtain a given signal of the second set of decorrelator input signals when performing the premixing for a second value of the complexity information.

The multi-channel decorrelator according to one of claims 16 to 18, wherein the multi-channel decorrelator is configured to combine at least four channel signals of the first set (Z) of N decorrelator input signals, wherein at least two of said at least four channel signals are associated with spatial positions on a left side of an audio scene, and wherein at least two of said at least four channel signals are associated with spatial positions on a right side of an audio scene, in order to obtain a given signal of the second set of decorrelator input signals when performing the premixing for a second value of the complexity information.

20. The multi-channel decorrelator according to one of claims 16 to 19, wherein the multi-channel decorrelator is configured to combine at least two channel signals of the first set (Z) of N decorrelator input signals which are associated with vertically spatially adjacent positions on a left side of the audio scene, in order to obtain a first decorrelator input signal of the second set of decorrelator input signals , and to combine at least two channel signals of the first set (Z) of N decorrelator input signals which are associated with vertically spatially adjacent positions on a right side of the audio scene, in order to obtain a second decorrelator input signal of the second set of decorrelator input signals for a first value of the complexity information, and

wherein the multi-channel decorrelator is configured to combine the at least two channel signals of the first set (z) of N decorrelator input signals which are associated with vertically spatially adjacent positions of the left side of the audio scene and the at least two channel signals of the first set (Z) of N decorrelator input signals which are associated with vertically spatially adjacent positions on the right side of the audio scene, in order to obtain a decorrelator input signal of the second set of decorrelator input signals for a second value of the complexity information,

wherein a number of decorrelator input signals of the second set of decorrelator input signals is larger for the first value of the complexity information than for the second value of the complexity information.

21. A multi-channel audio decoder (100;1550) for providing at least two output audio signals (1 12, 1 14;1552a-1552n) on the basis of an encoded representation (1 10; 1516a, 1516b, 1518),

wherein the multi-channel audio decoder comprises a multi-channel decorrelator (140; 600; 1590; 1700) according to one of claims 1 to 20.

22. The multi-channel audio decoder according to claim 21 ,

wherein the multi-channel audio decoder is configured to render a plurality of decoded audio signals (122; 1562a-1562n), which are obtained on the basis of the encoded representation, in dependence on one or more rendering parameters (132), to obtain a plurality of rendered audio signals (134, 136; 1582a-1582n), and

wherein the multi-channel audio decoder is configured to derive one or more decorrelated audio signals (142,144; 1592a-1592n) from the rendered audio signals using the multi-channel decorrelator, wherein the rendered audio signals constitute the first set of decorrelator input signals, and wherein the second set of decorrelator output signals constitute the decorrelated audio signals, and

wherein the multi-channel audio decoder is configured to combine (150;1598) the rendered audio signals, or a scaled version thereof, with the one or more decorrelated audio signals, to obtain the output audio signals.

The multi-channel audio decoder according to claim 21 or claim 22, wherein the multi-channel audio decoder is configured to select a premixing matrix (Mpre) for usage by the multi-channel decorrelator in dependence on a control information included in the encoded representation.

The multi-channel audio decoder according to one of claims 21 to 23, wherein the multi-channel audio decoder is configured to select a premixing matrix ( pre) for usage by the multi-channel decorrelator in dependence on an output configuration describing an allocation of the output audio signals with spatial positions of an audio scene.

The multi-channel audio decoder according to one of claims 21 to 24, wherein the multi-channel audio decoder is configured to select between three or more different premixing matrices (Mpre) for usage by the multi-channel decorrelator in dependence on a control information included in the encoded representation for a given output configuration, wherein each of the three or more different premixing matrices is associated with a different number of signals of the second set of K decorrelator input signals.

The multi-channel audio decoder according to one of claims 21 to 25, wherein the multi-channel audio decoder is configured to select a premixing matrix (Mpre) for usage by the mu!ti-channel decorreiator in dependence on a mixing matrix (Dconv, Drender) which is used by an format converter or renderer which receives the at least two output audio signals.

The multi-channel audio decoder according to claim 26, wherein the multi-channel audio decoder is configured to select the premixing matrix (Mpre) for usage by the multi-channel decorrelatorto be equal to a mixing matrix (Dconv, Drender) which is used by a format converter or renderer which receives the at least two output audio signals.

A multi-channel audio encoder (800) for providing an encoded representation (814) on the basis of at least two input audio signals (810;812),

wherein the multi-channel audio encoder is configured to provide one or more downmix signals (822) on the basis of the at least two input audio signals, and

wherein the multi-channel audio encoder is configured to provide one or more parameters (832) describing a relationship between the at least two input audio signals, and

wherein the multi-channel audio encoder is configured to provide a decorrelation complexity parameter (842) describing a complexity of a decorrelation to be used at the side of an audio decoder.

A method (900) for providing a plurality of decorrelated signals on the basis of a plurality of decorrelator input signals, the method comprising:

premixing (910) a first set of N decorrelator input signals into a second set of K decorrelator input signals, wherein KK'.

A method (1000) for providing at least two output audio signals on the basis of an encoded representation,

wherein the method comprises providing ( 020) a plurality of decorrelated signals on the basis of a plurality of decorrelator input signals according to claim 29.

A method (1 100) for providing an encoded representation on the basis of at least two input audio signals, the method comprising:

providing (1 1 10) one or more downmix signals on the basis of the at least two input audio signals, and

providing (1 120) one or more parameters describing a relationship between the at least two input audio signals, and

providing (1 130) a decorrelation complexity parameter describing a complexity of a decorrelation to be used at the side of an audio decoder.

A computer program for performing the method of claim 29, claim 30 or claim 31 when the computer program runs on a computer.

An encoded audio representation ( 200), comprising:

an encoded representation (1210) of a downmix signal;

an encoded representation (1220) of one or more parameters describing a relationship between the at least two input audio signals, and

an encoded decorrelation complexity parameter describing a complexity of a decorrelation to be used at the side of an audio decoder.