Method and apparatus for applying dynamic range compression to high-order Ambisonics signals

Abstract

To solve such a problem that dynamic range control (DRC) cannot be applied simply to a signal of high order ambisonics (HOA) based signal.SOLUTION: A method for executing DRC of a HOA signal includes to convert the HOA signal into space region, to analyze the converted HOA signal, and to obtain a gain factor usable for dynamic compression from the analysis results. The gain factor can be transmitted together with the HOA signal. When the DRC is applied, the HOA signal is converted into the space region, the gain factor is extracted, and multiplied by the converted HOA signal in the space region, thus obtaining a converted HOA signal subjected to gain compensation. The converted HOA signal subjected to gain compensation is converted into the original HOA region, thus obtaining a HOA signal subjected to gain compensation.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method and apparatus for performing Dynamic Range Compression (DRC) on Ambisonics signals, in particular Higher Order Ambisonics (HOA) signals. [Background technology]

[0002] The objective of Dynamic Range Compression (DRC) is to reduce the dynamic range of an audio signal. A time-varying gain factor is applied to the audio signal. Typically this gain factor depends on the amplitude envelope of the signal used to control the gain. The mapping is generally non-linear. Soft sounds are often amplified while large amplitudes are mapped to smaller amplitudes. Scenarios are noisy environments, late night listening, small speaker or mobile headphone listening.

[0003] A common concept for streaming or broadcasting audio is to generate DRC gains before transmission and apply these gains after reception and decoding. The principle of using DRC, i.e. how DRC is typically applied to an audio signal, is shown in Fig. 1a). The signal level, typically the signal envelope, is detected and an associated time-varying gain g DRC is calculated. The gain is used to change the amplitude of the audio signal. Figure 1b) shows the principle of using DRC for encoding / decoding, where the gain factor is transmitted together with the coded audio signal. At the decoder side, the gain is applied to the decoded audio signal in order to reduce its dynamic range.

[0004] For 3D audio, different gains can be applied to loudspeaker channels representing different spatial positions. These positions must then be known at the sender to be able to generate a matching set of gains. This is usually only possible for idealized conditions. In realistic cases, the number of speakers and their placement can vary in many ways. This is influenced more by practical considerations than specifications. Higher order Ambisonics is an audio format that allows flexible rendering. HOA signals are composed of coefficient channels that do not directly represent sound levels. Therefore, DRC cannot simply be applied to HOA-based signals. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2015 / 007889A (PD130040) [Non-patent literature]

[0006] [Non-Patent Document 1] J¨org Fliege, “Integration nodes for the sphere”, 2010, online, accessed 2010-10-05, http: / / www.mathematik.uni-dortmund.de / lsx / research / projects / fliege / nodes / nodes.html [Non-Patent Document 2] J¨org Fliege and Ulrike Maier, “A two-stage approach for computing cubature formula for the sphere”, Technical report, Fachbereich Mathematik, Universitat Dortmund, 1999 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention at least solves the problem of how DRC can be applied to HOA signals. [Means for solving the problem]

[0008] The HOA signal is analyzed to obtain one or more gain factors. In one embodiment, at least two gain factors are obtained and the analysis of the HOA signal includes a transformation to the spatial domain (iDSHT). The one or more gain factors are transmitted together with the original HOA signal. A special indicator can be transmitted to indicate whether all gain factors are equal. This is the case in the so-called simplified mode. In the non-simplified mode, on the other hand, at least two different gain factors are used. At the decoder, the one or more gain factors can be applied to the HOA signal (this is not mandatory). The user has the option of applying the one or more gain factors or not. The advantage of the simplified mode is that only one gain factor is used and the gain factor can be applied directly in the HOA domain to the coefficient channel of the HOA signal, thus skipping the transformation to the spatial domain and then back to the HOA domain, thus requiring significantly fewer calculations. In the simplified mode, the gain factors are obtained by analysis of only the zeroth order coefficients of the HOA signal.

[0009] According to an embodiment of the present invention, a method for performing DRC on an HOA signal includes transforming the HOA signal into the spatial domain (by an inverse DSHT), analyzing the transformed HOA signal, and obtaining from the result of said analysis a gain factor usable for dynamic range compression. In a further step, the obtained gain factor is multiplied with the transformed HOA signal (in the spatial domain) to obtain a gain-compressed transformed HOA signal. Finally, the gain-compressed transformed HOA signal is transformed back (by a DSHT) into the HOA domain, i.e. the coefficient domain, to obtain a gain-compressed HOA signal.

[0010] Furthermore, according to an embodiment of the present invention, a method for performing DRC in simplified mode on an HOA signal includes analyzing the HOA signal and obtaining from the result of said analysis a gain factor usable for dynamic range compression. In a further step, upon evaluation of the index, the obtained gain factor is multiplied with a coefficient channel of the HOA signal (in the HOA domain) to obtain a gain-compressed transformed HOA signal. Upon evaluation of the index, it may also be determined that the transformation of the HOA signal can be skipped. An index indicating the simplified mode, i.e., that only one gain factor is used, may be set either implicitly, e.g., when only the simplified mode is available due to hardware or other constraints, or explicitly, e.g., upon user selection of either the simplified mode or the non-simplified mode.

[0011] Furthermore, a method of applying a DRC gain factor to an HOA signal includes receiving an HOA signal, an index, and a gain factor, determining that the index indicates a non-simplified mode, transforming (using an inverse DSHT) the HOA signal to the spatial domain to obtain a transformed HOA signal, multiplying the transformed HOA signal by the gain factor to obtain a dynamic range compressed transformed HOA signal, and transforming (using a DSHT) the dynamic range compressed transformed HOA signal back to the HOA domain (i.e., the coefficient domain) to obtain a dynamic range compressed HOA signal. The gain factor can be received together with or separately from the HOA signal. Furthermore, according to an embodiment of the present invention, a method of applying a DRC gain factor to an HOA signal includes receiving an HOA signal, an index, and a gain factor, determining that the index indicates a simplified mode, and upon said determination, multiplying the HOA signal by the gain factor to obtain a dynamic range compressed HOA signal. The gain factor can be received together with or separately from the HOA signal.

[0012] An apparatus for applying a DRC gain factor to an HOA signal is disclosed in claim 11.

[0013] In one embodiment, the present invention provides a computer readable medium having executable instructions for causing a computer to carry out a method of applying a DRC gain factor to an HOA signal, the method including the steps as described above.

[0014] In one embodiment, the present invention provides a computer readable medium having executable instructions for causing a computer to carry out a method of performing DRC on an HOA signal, the method including the steps as described above.

[0015] Advantageous embodiments of the invention are disclosed in the dependent claims, the following description and the drawings. [Brief description of the drawings]

[0016] Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings. [Figure 1] FIG. 1 illustrates the general principle of DRC applied to audio. [Diagram 2] FIG. 2 illustrates a general approach for applying DRC to HOA-based signals according to the present invention. [Diagram 3] A diagram showing a spherical speaker lattice for N=1 to N=6. [Figure 4] FIG. 1 illustrates the generation of DRC gains for an HOA. [Diagram 5] FIG. 1 illustrates the application of DRC to an HOA signal. [Figure 6] FIG. 13 is a diagram showing a dynamic range compression process on the decoder side. [Figure 7] FIG. 13 illustrates the DRC for HOA in the QMF domain combined with the rendering stage. [Figure 8] FIG. 13 illustrates DRC for HOA in the QMF domain combined with a rendering stage for the simple case of a single DRC gain group. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The present invention describes how DRC can be applied to HOA. This is usually not straightforward since HOA is not a sound field description. Figure 2 illustrates the principle of the approach. At the encoding or transmitting side, as shown in Figure 2 a), the HOA signal is analyzed, a DRC gain g is calculated from the analysis of the HOA signal, and the DRC gain is coded and transmitted together with the coded representation of the HOA content. This can be a multiplexed bitstream or two or more separate bitstreams.

[0018] At the decoding or receiving side, a gain g is extracted from such bitstream(s), as shown in Fig. 2b). After decoding the bitstream in the decoder, the gain g is applied to the HOA signal as described below. This results in a gain being applied to the HOA signal, i.e., in general, a HOA signal with reduced dynamic range. Finally, the dynamic range adjusted HOA signal is rendered in the HOA renderer.

[0019] The assumptions and definitions used are explained below.

[0020] The assumption is that the HOA renderer is energy-preserving, i.e., N3D normalized spherical harmonics are used and the energy of the unidirectional signal, encoded inside the HOA representation, is preserved after rendering. For example, US Pat. No. 6,399,433 describes how to achieve this energy-preserving HOA rendering.

[0021] The definitions of terms used are as follows:

[0022]

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[0023]

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[0024]

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[0025] For all HOA truncation orders N, the ideal L L =(N+1) 2 virtual speaker lattices and associated rendering matrices D L are defined. The virtual speaker positions sample the spatial area surrounding the virtual listener. A grid for N=1 to 6 is shown in Figure 3, where the area associated with a speaker is the shaded cell. One sampling position is always relative to the central speaker position (azimuth=0, tilt=π / 2; note that the azimuth is measured from the front direction relative to the listening position). The sampling positions, D L , D L -1 is known at the encoder side when the DRC gain is generated. At the decoder side, D is used to apply the gain value. L and D. L -1 needs to be known.

[0026] The generation of the DRC gain for an HOA works as follows.

[0027] HOA signal is W L =D L These signals are then transformed into the spatial domain by B. By analyzing these signals, L L =(N+1) 2 DRC gain up to gl is generated. If the content is a combination of HOA and Audio Objects (AO), the AO signal, e.g. the dialogue track, may be used for side chaining. This is shown in Fig. 4b). When generating different DRC gain values ​​related to different spatial areas, care must be taken that these gains do not affect the spatial image stability at the decoder side. To avoid this, in the simplest case (the so-called simplified mode), a single gain may be assigned to all L channels. This can be done by analysing all spatial signals W or by using the zeroth-order HOA coefficient sample block.

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[0028] In Fig. 4, the generation of DRC gains for an HOA is shown. Fig. 4a) shows how a single gain g1 (for a single gain group) is added to the zeroth-order HOA component

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[0029] The gain value is transmitted to the receiver or decoder side.

[0030] Variable numbers 1 through L related to blocks of τ samples L =(N+1) 2 gain values ​​are transmitted. The gain values ​​can be assigned to channel groups for transmission. In one embodiment, all equal gains are combined into one channel group to minimize transmitted data. If a single gain is transmitted, it is L L The channel group gain value g lg and their number. The usage of the channel group is signaled so that the receiver or decoder can correctly apply the gain values.

[0031] The gain values ​​are applied as follows:

[0032] The receiver / decoder determines the number of encoded gain values ​​transmitted, decodes the associated information (51), and converts those gains into L L=(N+1) 2 In the case where only one gain value (one channel group) is transmitted, it can be directly applied to the HOA signal (52) (B DRC =g1B). This is advantageous because decoding is much simpler and requires significantly less processing, since no matrix operations are required and instead the gain values ​​can be directly applied 52, e.g. multiplied with the HOA coefficients.

[0033] When more than one gain is transmitted, the channel group gains are each represented by L channel gains g = [g1, ..., g L ] is assigned to.

[0034] For a hypothetical regular loudspeaker grid, the loudspeaker signal with the DRC gain applied is

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[0035] This is (N+1) 2This solution has the advantage over the conventional solution because it is more efficient in terms of the computational operations required, i.e., the decoding is much simpler and requires significantly less processing, since <τ. The reason is that no matrix operations are required, and instead the gain values ​​can be directly applied, i.e., multiplied to the HOA coefficients, in the gain assignment block 54.

[0036] In one embodiment, a more efficient way of applying the gain matrix is ​​to modify the renderer matrix in the renderer matrix modification block 57 as

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[0037] In summary, Figure 5 shows various embodiments of applying DRC to the HOA signal. In Figure 5a), a single channel group gain is transmitted, decoded (51), and applied directly to the HOA coefficients (52). The HOA coefficients are then rendered (56) using the regular rendering matrix.

[0038] In FIG. 5b), two or more channel group gains are transmitted and decoded (51). The result of the decoding is (N+1) 2 A gain vector g of gain values ​​is obtained. A gain matrix G is generated and applied to the block of HOA samples (54). These are then rendered using the regular rendering matrix.

[0039] In Fig. 5c), instead of applying the decoded gain matrix / gain values ​​directly to the HOA signals, we apply them directly to the renderer matrices. This is performed in the renderer matrix modification block 57. This is computationally beneficial if the DRC block size τ is larger than the number of output channels L. In this case, the HOA samples are rendered using the modified rendering matrix (57).

[0040] In the following, the computation of an ideal DSHT (Discrete Spherical Harmonic Transform) matrix for DRC is described. Such a DSHT matrix is ​​specifically optimized for use in DRC and differs from DSHT matrices used for other purposes, e.g. data rate compression.

[0041] The ideal rendering and encoding matrix D related to the ideal spherical layout L and D. L -1 The requirements for are derived below. Ultimately, these requirements are: (1) Rendering matrix D L must be invertible, i.e., D L -1 must be present; (2) the sum of amplitudes in the spatial domain should be reflected as the zeroth-order HOA coefficient after the transformation from the spatial domain to the HOA domain and should be preserved after the subsequent transformation back to the spatial domain (amplitude requirement); (3) The energy of the spatial signal should be preserved when transforming to the HOA domain and back to the spatial domain (energy conservation requirement).

[0042] Even for an ideal rendering layout, requirements 2 and 3 seem to contradict each other. When using a naive approach for deriving DSHT transformation matrices as known from the prior art, only one or the other of requirements (2) and (3) can be fulfilled without error. Fulfilling one of requirements (2) and (3) without error leads to an error of more than 3 dB for the other. This usually leads to audible artifacts. A way to overcome this problem is described below.

[0043] First, L=(N+1) 2 The ideal spherical layout with L directions of (virtual) speaker positions is selected. l and the associated mode matrix is

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[0044] The first prototype rendering matrix (D L ] is derived by the following formula:

[0045]

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[0046] Second, a compact singular value decomposition is performed:

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[0047]

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[0048] Fourth, in the final step, the amplitude error to satisfy requirement 2 is substituted: If the row vector e is

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[0049]

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[0050] The detailed requirements for DRC are explained below.

[0051] First, L with value g1 in the spatial domain L Applying the same gains is equivalent to applying the gain g1 to the HOA coefficients:

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[0052] Second, analyzing the sum signal in the spatial domain is equivalent to analyzing the zeroth-order HOA component. The DRC analyzer uses the energy of the signal and its amplitude. Thus, the sum signal is related to the amplitude and the energy.

[0053] HOA Signal Model

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[0054]

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[0055] The zeroth order component HOA signal needs to be summed with the directional signal to reflect the correct amplitude of the sum signal.

[0056]

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[0057] In this mix,

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[0058] The sum of the amplitudes in the spatial domain is the HOA pan matrix M L =D L Psi e Using

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[0059] this is,

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[0060] This also ensures that the energy requirement for the sum signal can be met. The energy sum in the spatial domain is

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[0061] this is,

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[0062] Third, conservation of energy is essential.

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[0063] RequirementsVV T = 1 means L ≧ (N + 1) 2 This can be achieved for L<(N+1) 2 can only be approximated.

[0064] As examples, cases with ideal spherical positions (HOA orders N=1 to N=3) are given below (Tables 1-3). Ideal spherical positions for further HOA orders (N=4 to N=6) are given at the end (Tables 4-6). All positions below are derived from the modified positions published in [1]. These positions and the associated quadrature / higher order quadrature gains were published in [2]. In these tables, azimuth angles are measured counterclockwise from the front direction relative to the listening position and tilt angles are measured from the z-axis with tilt 0 above the listening position.

[0065] [Table 1] Table 1: a) Spherical positions of virtual loudspeakers for HOA order N=1, b) Resulting rendering matrix for the spatial transformation (DSHT).

[0066] [Table 2] Table 2: a) Spherical positions of virtual loudspeakers for HOA order N=2, b) Resulting rendering matrix for spatial transformation (DSHT).

[0067] [Table 3] Table 3: a) Spherical positions of virtual loudspeakers for HOA order N=2, b) Resulting rendering matrix for spatial transformation (DSHT).

[0068] The term numerical quadrature, often abbreviated to quadrature, is entirely synonymous with numerical integration, especially when applied to one-dimensional integrals. Numerical integration in two or more dimensions is referred to herein as higher-order quadrature.

[0069] A typical application scenario for applying DRC gain to an HOA signal is shown above in Figure 5. For mixed content applications, such as HOA and audio objects, the DRC gain application can be realized in at least two ways for flexible rendering.

[0070] Fig. 6 exemplarily illustrates dynamic range compression (DRC) processing at the decoder side: in Fig. 6a) DRC is applied before rendering and mixing, in Fig. 6b) DRC is applied to the loudspeaker signals, i.e. after rendering and mixing.

[0071] In Fig. 6 a) DRC gains are applied separately to the audio objects and to the HOA. DRC gains are applied to the audio objects in the audio object DRC block 610 and DRC gains are applied to the HOA in the HOA DRC block 615. Here, the realization of the block HOA DRC block 615 corresponds to the one of Fig. 5. In Fig. 6 b) a single gain is applied to all channels of the mixed signal of the rendered HOA and the rendered audio object signals. Here, spatial emphasis and attenuation are not possible. The associated DRC gains cannot be generated by analyzing the sum signal of the rendered mix, since the speaker layout of the consumer site is not known at the time of production at the broadcast or content production site. The DRC gains are

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[0072]

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[0073] DRC on HOA Content The DRC may be applied to the HOA signal before rendering or combined with the rendering. The DRC for the HOA can be applied in the time domain or in the QMF filter bank domain.

[0074] For time-domain DRC, the DRC decoder calculates (N+1) 2 Gain values

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[0075] The DRC gain is

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[0076] In one embodiment, (N+1) per sample 4 To reduce the computational load by one operation, the loudspeaker signal is processed in a rendering stage.

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[0077] As in the simplified mode, all gains g1,…,g (N+1)2 The same value g drc , a single gain set was used to convey the encoder DRC gains. This case can be flagged by the DRC decoder. In this case, no computations are required in the spatial filter, so the computations are

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[0078] The above describes how to obtain and apply the DRC gain values. Below we describe the calculation of the DSHT matrix for the DRC.

[0079] In the following, D L D DSHT The name will be changed to Spatial Filter D. DSHT and its inverse D DSHT -1 The matrix for determining is calculated as follows:

[0080] A set of spherical positions, indexed by the HOA order N from Tables 1-4

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[0081]

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[0082] For DRC in the QMF filter bank domain the following holds:

[0083] The DRC decoder is (N+1) 2 Gain values ​​g for all time-frequency tiles n, m for spatial channels ch (n,m). The gain for time slot n and frequency band m is

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[0084] In the QMF filter bank domain, multi-band DRC is applied. The processing steps are shown in Figure 7. The reconstructed HOA signal is then processed by (inverse DSHT): DSHT =D DSHT It is transformed into the spatial domain by C, where

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[0085]

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[0086] Figure 7 shows the DRC for HOA in the QMF domain combined with the rendering stage. If only a single gain set for the DRC is used, this should be flagged by the DRC decoder, as this again allows for computational simplifications. In this case, all the gains in the vector g(n,m) have the same value g DRC (n,m). The QMF filter bank can be applied directly to the HOA signal, with gain g DRC(n,m) can be multiplied in the filter bank domain.

[0087] Figure 8 shows the DRC for an HOA in the QMF domain (Quadrature Mirror Filter domain) combined with a rendering stage, with a computational simplification for the simple case of a single DRC gain group.

[0088] As will become apparent in view of the above, in one embodiment, the present invention relates to a method for applying a dynamic range compression gain factor to an HOA signal, the method comprising the steps of receiving an HOA signal and one or more gain factors, transforming 40 the HOA signal into the spatial domain using an iDSHT with a transformation matrix derived from the spherical positions of virtual loudspeakers and a quadrature gain q to obtain a transformed HOA signal, multiplying the gain factor by the transformed HOA signal to obtain a dynamically range compressed transformed HOA signal, and transforming the dynamically range compressed transformed HOA signal back into the coefficient domain, the original HOA domain, using a Discrete Spherical Harmonics Transform (DSHT) to obtain a dynamically range compressed HOA signal.

[0089] Furthermore, the transformation matrix is

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[0090] Furthermore, in one embodiment, the present invention relates to an apparatus for applying a DRC gain factor to an HOA signal, the apparatus comprising a processor or one or more processing elements adapted to perform the steps of receiving an HOA signal and one or more gain factors, transforming 40 the HOA signal into the spatial domain using an iDSHT with a transformation matrix derived from the spherical positions of virtual loudspeakers and a quadrature gain q to obtain a transformed HOA signal, multiplying the gain factor by the transformed HOA signal to obtain a dynamically range compressed transformed HOA signal, and transforming the dynamically range compressed transformed HOA signal into the original HOA domain, which is the coefficient domain, using a Discrete Spherical Harmonics Transform (DSHT) to obtain a dynamically range compressed HOA signal. Furthermore, the transformation matrix is

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[0091] Furthermore, in one embodiment, the present invention relates to a computer-readable storage medium having computer-executable instructions that, when executed on a computer, cause the computer to perform a method for applying a dynamic range compression gain factor to a Higher Order Ambisonics (HOA) signal, the method including the steps of receiving an HOA signal and one or more gain factors, transforming 40 the HOA signal into the spatial domain using an iDSHT with a transformation matrix derived from the spherical positions of virtual loudspeakers and a quadrature gain q to obtain a transformed HOA signal, multiplying the gain factor by the transformed HOA signal to obtain a dynamic range compressed transformed HOA signal, and transforming the dynamic range compressed transformed HOA signal back into the coefficient domain, the original HOA domain, using a Discrete Spherical Harmonics Transform (DSHT) to obtain a dynamic range compressed HOA signal. Furthermore, the transformation matrix is

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[0092] Furthermore, in one embodiment, the present invention relates to a method for performing DRC on an HOA signal, the method includes the steps of: setting or determining a mode, which is either a simplified mode or a non-simplified mode; transforming the HOA signal into a spatial domain using an inverse DSHT in the non-simplified mode; analyzing the transformed HOA signal in the non-simplified mode; and obtaining one or more gain factors usable for dynamic range compression from the analysis result, where only one gain factor is obtained in the simplified mode and two or more different gain factors are obtained in the non-simplified mode; multiplying the obtained gain factor with the HOA signal in the simplified mode to obtain a gain-compressed HOA signal; and multiplying the obtained gain factor with the transformed HOA signal in the non-simplified mode to obtain a gain-compressed transformed HOA signal; and transforming the gain-compressed transformed HOA signal back to the HOA domain to obtain a gain-compressed HOA signal.

[0093] In one embodiment, the method further includes receiving an indicator indicating either a simplified mode or a non-simplified mode, selecting the non-simplified mode if the indicator indicates the non-simplified mode, and selecting the simplified mode if the indicator indicates the simplified mode, wherein the steps of converting the HOA signal to the spatial domain and converting the dynamic range compressed converted HOA signal back to the HOA domain are performed only in the non-simplified mode, and in the simplified mode, the HOA signal is multiplied by only one gain factor.

[0094] In one embodiment, the method further includes a step of analyzing the HOA signal in a simplified mode and analyzing a converted HOA signal in a non-simplified mode, and then obtaining one or more gain factors that can be used for dynamic range compression from the result of the analysis, where two or more different gain factors are obtained in the non-simplified mode and only one gain factor is obtained in the simplified mode, where in the simplified mode a gain-compressed HOA signal is obtained by multiplying the obtained gain factor with the HOA signal, and in the non-simplified mode the gain-compressed converted HOA signal is obtained by multiplying the obtained two or more gain factors with the converted HOA signal, and in the non-simplified mode, the conversion of the HOA signal to the spatial domain uses an inverse DSHT.

[0095] In one embodiment, the HOA signal is split into frequency subbands, and the gain factor(s) are derived separately for each frequency subband and applied with an individual gain per subband. In one embodiment, the steps of analyzing the HOA signal (or the transformed HOA signal), deriving one or more gain factors, multiplying the HOA signal (or the transformed HOA signal) with the derived gain factor, and converting the gain-compressed transformed HOA signal back to the HOA domain are applied separately for each frequency subband with an individual gain per subband. It is noted that the sequential order of splitting the HOA signal into frequency subbands and converting the HOA signal to the spatial domain can be interchanged and / or the sequential order of combining the subbands and converting the gain-compressed transformed HOA signal back to the HOA domain can be interchanged. These interchanges can be independent of each other.

[0096] In one embodiment, the method further comprises transmitting the converted HOA signal together with the obtained gain factors and a number of these gain factors prior to the step of multiplying by the gain factors.

[0097] In one embodiment, the transformation matrix is ​​a mode matrix ΨDSHT and the corresponding quadrature gains are calculated from the modal matrix Ψ DSHT teeth

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[0098] In one embodiment, the HOA signal B is transformed into the spatial domain to produce a transformed HOA signal W DSHT The converted HOA signal W DSHT is the gain value diag(g)

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[0099] In one embodiment, at least (N+1) 2 If <τ, the method further comprises:

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[0100] In one embodiment, the method further comprises: decomposing the gain matrix G by at least L<τ, where L is a number of output channels and τ is a DRC block size.

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[0101] In one embodiment, the present invention relates to a method for applying a DRC gain factor to an HOA signal, the method comprising the steps of: receiving an HOA signal together with an index and one or more gain factors, the index indicating either a simplified mode or a non-simplified mode, and only one gain factor being received when the index indicates the simplified mode; selecting either a simplified mode or a non-simplified mode according to the index; and in the simplified mode, multiplying the gain factor with the HOA signal to obtain a dynamic range compressed HOA signal, and in the non-simplified mode, transforming the HOA signal into a spatial domain to obtain a transformed HOA signal, multiplying the gain factor with the transformed HOA signal to obtain a dynamic range compressed transformed HOA signal, and transforming the dynamic range compressed transformed HOA signal back to the HOA domain to obtain a dynamic range compressed HOA signal.

[0102] Furthermore, in one embodiment, the present invention relates to an apparatus for performing DRC on an HOA signal, the apparatus having a processor or one or more processing elements adapted to perform the following steps: set or determine a mode, either a simplified mode or a non-simplified mode; transform the HOA signal into the spatial domain using an inverse DSHT in the non-simplified mode; analyze the transformed HOA signal in the non-simplified mode; and obtain from the analysis one or more gain factors usable for dynamic range compression, where in the simplified mode only one gain factor is obtained and in the non-simplified mode two or more different gain factors are obtained; multiply the obtained gain factor by the HOA signal in the simplified mode to obtain a gain compressed HOA signal, and in the non-simplified mode multiply the obtained gain factor by the transformed HOA signal to obtain a gain compressed transformed HOA signal, and transform the gain compressed transformed HOA signal back to the HOA domain to obtain a gain compressed HOA signal.

[0103] In an embodiment for non-simplified mode only, the device for performing DRC on the HOA signal comprises a processor or one or more processing elements adapted to perform the steps of: analyzing the transformed HOA signal, obtaining from the result of said analysis one or more gain factors usable for dynamic range compression, multiplying the obtained gain factors with said transformed HOA signal to obtain a gain-compressed transformed HOA signal, and converting the gain-compressed transformed HOA signal back to the HOA domain to obtain a gain-compressed HOA signal. In an embodiment, the device further comprises a transmitting unit for transmitting the HOA signal together with the obtained gain factor(s) before multiplying with the obtained gain factor(s).

[0104] Furthermore, in an embodiment, the present invention relates to an apparatus for applying a DRC gain factor to an HOA signal, the apparatus comprising a processor or one or more processing elements adapted to perform the steps of: receiving an HOA signal together with an index and one or more gain factors, the index indicating either a simplified mode or a non-simplified mode, and only one gain factor being received if the index indicates the simplified mode; selecting either the simplified mode or the non-simplified mode according to the index; and in the simplified mode, multiplying the gain factor with the HOA signal to obtain a dynamic range compressed HOA signal, and in the non-simplified mode, transforming the HOA signal into the spatial domain to obtain a transformed HOA signal, multiplying the gain factor with the transformed HOA signal to obtain a dynamic range compressed transformed HOA signal, and transforming the dynamic range compressed transformed HOA signal back to the HOA domain to obtain a dynamic range compressed HOA signal.

[0105] Moreover, in one embodiment, the apparatus further comprises a transmitting unit for transmitting the HOA signal together with the obtained gain factor before multiplying with the obtained gain factor. In one embodiment, the HOA signal is divided into frequency subbands, and the analyzing the transformed HOA signal, obtaining a gain factor, multiplying the transformed HOA signal with the obtained gain factor and converting the gain compressed transformed HOA signal back to the HOA domain are applied to each frequency subband separately, using individual gains for each subband.

[0106] In one embodiment of an apparatus for applying DRC gain factors to an HOA signal, the HOA signal is divided into multiple frequency subbands, and obtaining one or more gain factors, multiplying the obtained gain factors with the HOA signal or the transformed HOA signal, and in a non-simplified mode, converting the gain-compressed transformed HOA signal back to the original HOA signal is applied to each frequency subband separately, using individual gains for each subband.

[0107] Furthermore, in an embodiment where only the non-simplified mode is used, the present invention relates to an apparatus for applying a DRC gain factor to an HOA signal, the apparatus comprising a processor or one or more processing elements adapted to perform the steps of receiving an HOA signal together with a gain factor, transforming the HOA signal into the spatial domain (using an iDSHT) to obtain a transformed HOA signal, multiplying the gain factor by the transformed HOA signal to obtain a dynamically range compressed transformed HOA signal, and transforming the dynamically range compressed transformed HOA signal back into the HOA domain (i.e. the coefficient domain) (using a DSHT) to obtain a dynamically range compressed HOA signal.

[0108] Tables 4-6 below list the spherical positions of virtual loudspeakers for HOA of order N, where N=4, 5 or 6.

[0109] While the basic novel features of the invention have been shown, described and pointed out as applied to its preferred embodiments, it will be understood that various omissions, substitutions and changes in the described apparatus and methods may be made by those skilled in the art in the form and details of the disclosed devices and their operation without departing from the spirit of the invention. Any combination of elements that perform substantially the same function in substantially the same way to achieve the same results is expressly intended to be within the scope of the invention. Substitution of elements from one described embodiment for another described embodiment is also fully intended and contemplated.

[0110] It will be understood that the invention has been described purely by way of example and modifications of detail can be made without departing from the scope of the invention. Each feature disclosed in the description and (where appropriate) the claims and drawings may be provided independently or in any appropriate combination. Features may, where appropriate, be implemented in hardware, software or a combination of both.

[0111] [Table 4] Table 4: Spherical positions of virtual loudspeakers for HOA order N=4.

[0112] [Table 5] Table 5: Spherical positions of virtual loudspeakers for HOA order N=5.

[0113] [Table 6] Table 6: Virtual loudspeaker spherical positions for HOA order N=6.

Claims

1. 1. A method for dynamic range compression (DRC) comprising: receiving a reconstructed Higher Order Ambisonics (HOA) audio signal representation; The reconstructed HOA audio signal [Number 91] Transforming to the spatial domain based on D DSHT corresponds to the inverse discrete spherical harmonic transform (DSHT) matrix, C corresponds to a block of τ HOA samples, W corresponds to a block of spatial samples that match the input time granularity of the quadrature mirror filter (QMF) bank, and D DSHT teeth [Number 92] A matrix determined based on [Number 93] Based on this, Ψ DSHT is determined based on a transposed modal matrix of spherical harmonics associated with a virtual speaker, q is determined based on a quadrature gain associated with a set of spatial locations, and N is the order of the HOA audio signal representation; [Number 93B] Stages and; The DRC gain value g(n,m) corresponding to the time-frequency tile (n,m) is [Number 94] applying the method according to [Number 95] is the vector of spatial channels for time-frequency tile (n,m), and To the loudspeaker channel [Number 96] Rendering based on D DSHT -1 The matrix is ​​D DSHT matrix inverse, D is the HOA rendering matrix, method.

2. The method of claim 1 , wherein the reconstructed HOA audio representation is divided into frequency subbands and the DRC gain value is applied to each subband separately.

3. A non-transitory computer readable storage medium having computer executable instructions that, when executed on a computer, cause the computer to perform the method of claim 1.

4. 1. An apparatus for dynamic range compression (DRC), comprising: a receiver for receiving a reconstructed Higher Order Ambisonics (HOA) audio signal representation; and an audio decoder, the audio decoder comprising: The reconstructed HOA audio signal [Number 97] Transforming to the spatial domain based on D DSHT corresponds to the inverse discrete spherical harmonic transform (DSHT) matrix, C corresponds to a block of τ HOA samples, W corresponds to a block of spatial samples that match the input time granularity of the quadrature mirror filter (QMF) bank, and D DSHT teeth [Number 98] A matrix determined based on [Number 99] Based on this, Ψ DSHT is determined based on a transposed modal matrix of spherical harmonics associated with a virtual speaker, q is determined based on a quadrature gain associated with a set of spatial locations, and N is the order of the HOA audio signal representation; [Number 99B] Stages and; The DRC gain value g(n,m) corresponding to the time-frequency tile (n,m) is [Number 100] applying the method according to [Number 101] is the vector of spatial channels for time-frequency tile (n,m), and To the loudspeaker channel [00102] Rendering based on D DSHT -1 The matrix is ​​D DSHT where D is the inverse of the matrix D, and D is the HOA rendering matrix; Device.

5. The apparatus of claim 4 , wherein the reconstructed HOA audio representation is divided into frequency subbands and the DRC gain value is applied to each subband separately.

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