Apparatus and method for head-related transfer function compression - Patents.com

Abstract

An apparatus is provided, comprising: a rendering information processor (110) configured to modify original binaural rendering information in dependence on directional information to obtain modified binaural rendering information with adjusted spectral distortion.

Description

[Technical field]

[0001] The present invention relates to audio signal coding, processing and decoding, in particular to an apparatus and method for binaural rendering, and more particularly to an apparatus and method for head-related transfer function (HRTF) compression and expansion. [Background technology]

[0002] When sound waves are emitted from a speaker to a listener's ear, the sound is modified multiple times, for example by the reflection of the sound waves on walls, so that the sound that reaches the pinna of the ear contains, in addition to music and speech for example, information about the listening environment.

[0003] In addition, sounds arriving from multiple directions are shaped differently in the listener's head and pinnae. Using this information, the listener's brain can determine the approximate direction and distance of the sound source.

[0004] However, when headphones are used, all such information is usually missing, as the audio is emitted more or less directly to the listener's eardrums, which creates the impression that the sound is generated inside the listener's head, which can be perceived as inconvenient and can result in, for example, spectral coloration, especially when earphones are used for longer periods of time.

[0005] It has been determined that the above-mentioned modifications of the sound waves toward the pinna and eardrum of the listener can be measured and replicated by digital filters, for example, by using head-based impulse responses, head-related transfer functions, binaural room impulse responses, and binaural room transfer functions. When such filters are applied to audio signals to be reproduced by headphones or earphones, a spatial sound is created that creates a realistic sound impression. Such audio signal processing is called binaural processing or binaural rendering.

[0006] A head-related transfer function (HRTF) is an acoustic transfer function from a sound source to the two ears. An HRTF contains the location information of the corresponding sound source. A virtual sound from a particular direction, when heard through headphones, can be generated by convolution of the audio signal with the corresponding HRTF.

[0007] To render spatial sound binaurally, the HRTFs of relevant positions around the listener are measured and stored. The magnitudes of the HRTFs are frequency dependent and provide the essential psychoacoustic cues for a plausible binaural effect. However, their variations across frequency inevitably result in spectral distortions of the audio signal after binauralization.

[0008] The degree to which the signal is spectrally distorted may be more or less tolerable depending on several factors, e.g. the type of input signal (e.g. speech, music, ambience, special effects, etc.), the frequency spectrum of the signal, the frequency spectrum of the HRTFs, whether dynamic head tracking is used during binaural playback, and the distribution of the signal around the head.

[0009] If the magnitude of the HRTF is flattened across frequency, signal distortion can be reduced. This flattening is hereafter referred to as HRTF compression. Similarly, spectral magnitude emphasis can be achieved by the inverse, called HRTF expansion, which increases the spectral distortion of the input signal. To avoid redundancy, when referring to "HRTF compression" below, the term "HRTF compression" includes HRTF compression and HRTF expansion, given the understanding that "expansion" is simply "negative compression". There is no algorithmic difference between compression and expansion.

[0010] There is a trade-off between using uncompressed HRTFs, which provide complete cues for a reasonable binaural rendering but at the risk of spectral distortion of the binaural audio signal, and, on the other hand, using compressed HRTFs, which provide less effective cues for a reasonable binaural rendering but at the risk of spectral distortion of the binaural audio signal.

[0011] [1] and [2] describe modifications of HRTF filters to reduce undesirable timbral effects. This technique also reduces the root-mean-square (RMS) spectral variation of the HRTFs to reduce undesirable timbral coloration.

[0012] [3] describes the effects of magnitude compression or flattening on perceptual outcomes (e.g., externalization).

[0013] In [4] and [5] concepts are presented for only partial binaural virtualization of single-channel audio signals by filtering. Control allows a smooth transition between full binaural virtualization based on HRTFs and non-binaural virtualization corresponding to panning.

[0014] [6], [7], and [8] provide concepts that generally attempt to reduce spectral distortions, but such concepts seem to affect the overall spatial impression and require complex operations or transformations such as Principal Component Analysis (PCA).

[0015] Concepts have been described in [8] and [9] that attempt to compress HRTFs to reduce redundancy and reduce the amount of data stored. An HRTF representation is stored / transmitted that requires less data space than the original dataset. The HRTFs are restored before rendering, and the parameterization and reconstruction process also affects the HRTF magnitude spectrum, often flattening it. The concepts provided in [8] and [9] operate on the entire set of HRTFs and do not treat HRTFs from specific angles differently, and therefore do not provide direct control over the perceptual outcome.

[0016] It would be ideal to achieve good localization and externalization without distorting the spectrum of the input signal (thus preserving the artistic intent). Summary of the Invention [Problem to be solved by the invention]

[0017] It is an object of the present invention to provide an improved concept for binaural rendering. [Means for solving the problem]

[0018] The object of the present invention is solved by an apparatus according to claim 1, a method according to claim 24 and a computer program according to claim 25.

[0019] An apparatus is provided, comprising: a rendering information processor configured to modify original binaural rendering information in dependence on directional information to obtain modified binaural rendering information with adjusted spectral distortion.

[0020] Additionally provided is a method, comprising: Modifying the original binaural rendering information to obtain modified binaural rendering information in which the spectral distortion is adjusted depending on the directional information. Includes.

[0021] Also a computer program for carrying out the above-mentioned method when executed on a computer or signal processor.

[0022] In contrast to some embodiments of the present invention, the concepts presented in [1] and [2] do not algorithmically adjust the amount of compression based on the azimuth and elevation angles of the HRTF angles, thus flattening the HRTF magnitude spectrum by the same amount in all directions. Furthermore, the concepts in [1], [2] operate on HRTF pairs using the joint RMS spectrum of the original left-ear and right-ear filters, whereas embodiments of the present invention use a single HRTF filter, thus better preserving the RMS difference between ears. Furthermore, embodiments provide a concept to parametrically adjust the compression by weighting the compression ratio in multiple dimensions.

[0023] In contrast to some embodiments, [3] does not provide an algorithmic approach on how to adjust the smoothing to maintain good quality.

[0024] In contrast to some embodiments of the present invention, the concepts presented in [4] and [5] do not provide a parametric frequency-dependent compression approach, and do not provide an approach for the entire database of HRTFs.

[0025] According to an embodiment, spectral distortions in binaural rendering are adjusted.

[0026] In some embodiments, for example, spatial impression may be taken into account.

[0027] According to some embodiments, for example, one or more HRTFs may be processed.

[0028] In some embodiments, one or more HRTFs may be processed, for example, in the frequency domain.

[0029] According to some embodiments, the HRTF magnitude spectrum may be processed, for example, in the frequency domain.

[0030] In some embodiments, the HRTF magnitude spectrum may be, for example, compressed or expanded.

[0031] According to some embodiments, the HRTF magnitude spectrum can be parametrically compressed or expanded, for example, by taking into account one or more parameters.

[0032] In some embodiments, one of the one or more parameters may be, for example, an elevation angle of one or more HRTFs.

[0033] According to some embodiments, one of the one or more parameters may be, for example, an azimuth angle of one or more of the HRTFs.

[0034] In some embodiments, one of the one or more parameters may be, for example, a frequency.

[0035] According to some embodiments, for example, special treatment of frontal sound sources can be provided.

[0036] In some embodiments, for example, an offset may be provided for special treatment of frontal sound sources.

[0037] Some embodiments provide HRTF dynamics compression, which provides a means to compress the spectral magnitude of the HRTFs in an azimuth, elevation, and frequency dependent manner so that cues in important regions can be preserved, but the magnitude of the HRTFs can be controlled in different angular regions to control the spectral distortion and timbre coloration of the resulting binaural output signal.

[0038] According to some embodiments, smooth HRTF compression ratios are provided across angle (az,ele) and frequency. Applying these coefficients to the HRTF reduces spectral distortions while preserving the best possible spatial impression.

[0039] In an embodiment, the tonal distortion of HRTFs can be reduced, for example, by reducing their spectral dynamics (direction dependent) while preserving the spatial impression.

[0040] Some embodiments may, for example, only act on the frequency magnitude of the HRTFs, without modifying the phase.

[0041] Spectral peaks and phases are essential components of any HRTF, especially elevated HRTFs. Peaks and phases are also specific to the particular orientation (azimuth, elevation) of that HRTF. Although peaks and phases are essential properties for synthesizing binaural audio, they introduce spectral distortions. Embodiments can provide HRTF compression measures to control the tradeoff between, for example, spectral distortion and spatial effects.

[0042] In one embodiment, the magnitude of each frequency bin may be modified, for example, to be closer (compressed) or farther (expanded) from the root mean square magnitude of the frequency band of the HRTF.

[0043] According to some embodiments, the amount of compression applied to each HRTF may be weighted depending on the azimuth angle, so that frontal HRTFs, for example, get more compression and rear HRTFs less, and / or depending on the elevation angle, so that horizontal HRTFs, for example, get more compression and elevated ones less.

[0044] In one embodiment, the amount of compression may be modified uniquely for a selected angular focal region, for example, for a central HRTF at or near azimuth angle 0.0.

[0045] According to one embodiment, for example, different amounts of compression may be applied across different frequency regions.

[0046] In an embodiment, for example, by using HRTF dynamics compression according to one embodiment, excellent localization and externalization is provided without distorting the spectrum of the input signal (thus preserving the artistic intent).

[0047] In the following, embodiments of the invention will be explained in more detail with reference to the drawings. [Brief description of the drawings]

[0048] [Figure 1] 1 is an apparatus according to an embodiment. [Diagram 2] 1 is an apparatus for binaural rendering according to one embodiment. [Diagram 3] FIG. 13 illustrates compression for different vsp_angle_factor values ​​without applying center_offset, according to one embodiment. [Figure 4] 13 illustrates the effect of center_offset on overall compression value according to one embodiment. [Diagram 5] FIG. 2 illustrates an overall HRTF compression process according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0049] FIG. 1 is a diagram illustrating an apparatus according to one embodiment. The apparatus comprises a rendering information processor 110 configured to modify the original binaural rendering information in dependence on the directional information to obtain modified binaural rendering information in which the spectral distortions have been adjusted.

[0050] According to an embodiment, the rendering information processor 110 may be configured to modify the original binaural rendering information, for example such that the degree of adjustment of the spectral distortion depends on the directional information.

[0051] In one embodiment, the binaural rendering information may be suitable to be used for processing one or more audio input signals, for example to obtain a binaural signal comprising two audio channels.

[0052] FIG. 2 shows an embodiment in which the apparatus further comprises a signal processor (120) configured to process the one or more audio input signals depending on the modified binaural rendering information to obtain the binaural signal comprising the two audio channels.

[0053] According to one embodiment, the original binaural rendering information comprises one or more original head-related transfer function pairs, each of the one or more original head-related transfer function pairs comprising a first original head-related transfer function and a second original head-related transfer function. Depending on the directional information, the rendering information processor 110 may be configured to modify the first original head-related transfer function and / or the second original head-related transfer function of each of the one or more original head-related transfer function pairs, for example to obtain a first modified head-related transfer function and / or a second modified head-related transfer function of each of the one or more original head-related transfer function pairs.

[0054] In one embodiment, the signal processor 120 may be configured to process the one or more audio input signals in dependence on at least one modified head-related transfer function pair of the one or more modified head-related transfer function pairs, for example to obtain the binaural signal.

[0055] According to one embodiment, each of the first original head-related transfer function and the second original head-related transfer function of each of the one or more original head-related transfer function pairs, and each of the first modified head-related transfer function and the second modified head-related transfer function of each of the one or more modified head-related transfer function pairs, may be, for example, a head-related transfer function, or may be, for example, a head-related impulse response, or may be, for example, a binaural room transfer function, or may be, for example, a binaural room impulse response.

[0056] In one embodiment, the signal processor 120 may comprise, for example, one or more audio filters for applying a first modified head-related transfer function and / or a second modified head-related transfer function of at least one of one or more head-related transfer function pairs on the audio input signal.

[0057] In one embodiment, the rendering information processor 110 may be configured to process, for example, the first original head-related transfer function and / or the second original head-related transfer function of each of one or more head-related transfer function pairs in the frequency domain.

[0058] According to one embodiment, the rendering information processor 110 may be configured to modify the first original head-related transfer function and / or the second original head-related transfer function of each original head-related transfer function pair of one or more head-related transfer function pairs in dependence on the directional information, for example such that the magnitude spectrum of the first original head-related transfer function and / or the magnitude spectrum of the second original head-related transfer function of the original head-related transfer function pair is modified.

[0059] In one embodiment, for example, the rendering information processor 110 may be configured to modify the first original head-related transfer function and / or the second original head-related transfer function of each original head-related transfer function pair of one or more head-related transfer function pairs in dependence on the directional information, such that at least one magnitude difference between two frequency bands of the first original head-related transfer function and / or the second original head-related transfer function of the original head-related transfer function pair is corrected.

[0060] In one embodiment, if the directional information indicates, for example, that spectral distortion should be reduced, the rendering information processor 110 may be configured to modify the first original head-related transfer function and / or the second original head-related transfer function of each original head-related transfer function pair of one or more head-related transfer function pairs in dependence on the directional information, such that at least one magnitude difference between two frequency bands of the first original head-related transfer function and / or the second original head-related transfer function of the original head-related transfer function pair is reduced.

[0061] In one embodiment, the directional information may, for example, include directional information for each of the one or more head-related transfer function pairs.

[0062] According to an embodiment, the directional information of each of the one or more head-related transfer function pairs comprises an elevation angle and / or an azimuth angle of the head-related transfer function pair. The rendering information processor 110 may be configured to, for example, modify the first original head-related transfer function and / or the second original head-related transfer function of the original head-related transfer function pair depending on the elevation angle and / or the azimuth angle of the head-related transfer function pair.

[0063] In one embodiment, the rendering information processor 110 may be configured to determine one or more modification parameters, for example, depending on the directional information. The rendering information processor 110 may be configured to modify the first original head-related transfer function and / or the second original head-related transfer function of each of the one or more original head-related transfer function pairs, for example, depending on at least one of the one or more modification parameters. Each of the one or more modification parameters indicates a degree of adjustment of the spectral distortion.

[0064] According to an embodiment, the rendering information processor 110 may be configured to determine one or more modification parameters, for example by determining at least one of the one or more modification parameters for each of the one or more head-related transfer function pairs in dependence on the elevation angle and / or in dependence on the azimuth angle of the head-related transfer function pair, each of the modification parameters of the head-related transfer function pairs indicating a degree of adjustment of a spectral distortion in the first modified head-related transfer function and / or the second modified head-related transfer function of the modified head-related transfer function pair compared to a spectral distortion in the first original head-related transfer function and / or the second original head-related transfer function of the original head-related transfer function pair.

[0065] In an embodiment, the rendering information processor 110 may be configured to determine the at least one modification parameter for each of the one or more head-related transfer function pairs, for example in a frequency-dependent manner.

[0066] According to one embodiment, the rendering information processor 110 may be configured to generate the at least one correction parameter for each head transfer function pair of the one or more head transfer function pairs such that, for example, when the azimuth angle of the head transfer function pair indicates the presence of a frontal sound source, the correction parameter may be generated in a different way for the same value of the elevation angle of the head transfer function pair compared to when the azimuth angle of the head transfer function pair does not indicate the presence of a frontal sound source.

[0067] In one embodiment, the rendering information processor 110 may be configured to generate the at least one correction parameter for each head transfer function pair of the one or more head transfer function pairs, for example by generating an offset value that depends on the elevation angle of the head transfer function pair when the azimuth angle of the head transfer function pair indicates the presence of the frontal sound source.

[0068] According to an embodiment, the one or more original head-related transfer function pairs are a plurality of original head-related transfer function pairs, and the directional information comprises different directional information for each of the plurality of head-related transfer function pairs. The rendering information processor 110 may be configured to modify a first original head-related transfer function and / or a second original head-related transfer function of each of the plurality of original head-related transfer function pairs in dependence on the directional information of the original head-related transfer function pair to obtain a first modified head-related transfer function and / or a second modified head-related transfer function of each of the one or more modified head-related transfer function pairs, which are a plurality of modified head-related transfer function pairs. The signal processor 120 may be configured to process one or more audio input signals in dependence on the at least one modified head-related transfer function pair of the plurality of modified head-related transfer function pairs in order to obtain the binaural signal, for example.

[0069] In one embodiment, the signal processor 120 may be configured to process one or more audio input signals depending on one or more interpolated head-related transfer function pairs, for example to obtain a binaural signal. The rendering information processor 110 may be configured to determine the interpolated head-related transfer functions, for example including a first interpolated head-related transfer function and a second interpolated head-related transfer function. The rendering information processor 110 may be configured to determine the first interpolated head-related transfer function, for example by interpolating between the first head-related transfer function of each of at least two head-related transfer function pairs of the plurality of head-related transfer function pairs depending on the directional information. Furthermore, the rendering information processor 110 may be configured to determine the second interpolated head-related transfer function, for example by interpolating between the second head-related transfer function of each of at least two head-related transfer function pairs of the plurality of head-related transfer function pairs depending on the directional information.

[0070] Specific embodiments are described below. In the following, when reference is made to a head-related transfer function, such reference should be understood as an example of a particular embodiment. The concepts provided are equally applicable with respect to the time domain of the head-related impulse response, and equally applicable to binaural room transfer functions and binaural room impulse responses. The term "head-related transfer function" includes head-related transfer functions, head-related impulse responses, binaural room transfer functions, and binaural room impulse responses.

[0071] For example, HRTFs measured in the quadrature mirror filter (QMF) domain are considered "uncompressed." The most extreme version of HRTF compression results in a flat line across all frequencies. In such an extreme version of HRTF compression, the magnitude of all QMFs at all frequency bins is equal to the root mean square (RMS) of the uncompressed HRTFs.

[0072] According to some embodiments, the HRTF compression stage provides a way to smoothly move between these two states of "uncompressed" and "fully compressed", taking into account the possible sound arrival directions, i.e., azimuth and elevation angles around the listener's head.

[0073] In some embodiments, a compression ratio that depends on the correction parameters, e.g., azimuth and elevation, can be calculated, e.g., for each HRTF pair. In one embodiment, one compression ratio for both left and right ears for a particular azimuth and elevation can be calculated, e.g., in one embodiment. This factor can be further weighted, e.g., per frequency band, e.g., per QMF band, in one embodiment. This factor can be applied, e.g., to the corresponding frequency band of the corresponding HRTF. In another embodiment, two compression ratios for left and right ears for a particular azimuth and elevation can be calculated, e.g.,

[0074] According to one embodiment, compression can be applied parametrically, for example, depending on three parameters: azimuth, elevation, and frequency. In one embodiment, compression can include the possibility to specifically reduce compression for a particular angular focal region (e.g., when the azimuth angle is equal to or close to 0°). This provides flexible compression settings for directions where timbre-sensitive signals such as speech and vocals are typically located.

[0075] The provided concepts can take into account, for example, HRTF angles, and can keep the variation of the HRTF magnitude spectrum relatively high at angles that are considered to be highly relevant for binaural rendering, for example, to preserve spatial cues. An advantage of some embodiments is that the concepts can be, for example, highly customizable, such that the gradual changes in compression, for example as a function of azimuth, elevation, and frequency, can be tailored to best suit, for example, the input content and / or the intent of the binaural rendering.

[0076] In the following, specific embodiments are provided. A set of Head Related Transfer Functions (HRTFs) can be, for example, an input for the calculation of the compression ratio. The set of HRTFs can be, for example, defined as a number of HRTFs for different combinations of azimuth and elevation angles.

[0077] The HRTFs can be transferred to the frequency domain, for example, using a QMF filter bank.

[0078] The compression ratio can then be calculated, for example, for each HRTF and each QMF domain frequency band.

[0079] For example, for frequency band 1, the compression ratio may, for example, always be set to 1.0 for all HRTFs. For QMF bands 2-64, a loop may be performed over all HRTFs and one compression ratio may be calculated per HRTF pair (left and right ear) per QMF band, for example, as defined in the following pseudocode: % compression factor hrtfComp_vspBaselineFactor = 1.0; % angle-dependence for compression factor hrtfComp_vspAzimuthFactor_anchor_horizontal = 0.25; hrtfComp_vspAzimuthFactor_anchor_elevated = 0.05; % centre offset hrtfComp_centerOffset_anchor_horizontal = 0.10; hrtfComp_centerOffset_anchor_elevated = 1.00; % weight the compression factor dependent on the angle and elevation compressionAngleFactor = cosd(abs(hrtf_elevations(i))); compressionAngleFactor = (compressionAngleFactor - cosd(hrtfComp_el2compress)) * ... ((hrtfComp_vspAzimuthFactor_anchor_horizontal - hrtfComp_vspAzimuthFactor_anchor_elevated) / ... (1 - cosd(hrtfComp_el2compress))) + hrtfComp_vspAzimuthFactor_anchor_elevated; compression2apply = hrtfComp_vspBaselineFactor * abs(sind(hrtf_azimuths(i) / 2)^compressionAngleFactor); % compute the weighting for the center (az=0) if (hrtf_azimuths(i)==0) compressionCenterOffset = sind(abs(hrtf_elevations(i))); compressionCenterOffset = compressionCenterOffset * ... ((hrtfComp_centerOffset_anchor_elevated - hrtfComp_centerOffset_anchor_horizontal) / ... sind(hrtfComp_el2compress)) + hrtfComp_centerOffset_anchor_horizontal; compression2apply = compression2apply + compressionCenterOffset; end % compute RMS before compression over all frequencies for e = 1:2 % L / R ears input_rms(e) = rms( squeeze(hrtf(:, e, i)) ); for b = 2:64 % QMF bands % apply compression hrtf(b, e, i) = input_rms(e) + ( (hrtf(b, e, i) - input_rms(e)) * compression2apply); end end The resulting compression ratio ranges from 0.0 (fully compressed) to 1.0 (no compression) for each HRTF and each band. It depends on three parameters:

[0080] The baseline compression is defined by hrtfComp_vspBaselineFactor, which defines an overall upper limit for compression. This may be set, for example, by default to 1.0 with a range between 0.0 (fully compressed) and 1.0 (no compression). Other values ​​may be used, for example. For example, in another embodiment, 0 may indicate, for example, full compression and 100 may indicate, for example, no compression. In one embodiment, the baseline compression may set, for example, an upper limit for compression, which may typically be lower than this value, for example, because additional azimuth and elevation weighting may be applied.

[0081] compressionAngleFactor defines the elevation-dependent weighting. It is bounded by compressionAngleFactor at 0° elevation defined by hrtfComp_vspAzimuthFactor_anchor_horizontal and compressionAngleFactor at 90° elevation defined by hrtfComp_vspAzimuthFactor_anchor_elevated. Between + / -90° and 0° intermediate values ​​can be calculated using, for example, a cosine function. % angle-dependence for compression factor hrtfComp_vspAzimuthFactor_anchor_horizontal = 0.25; hrtfComp_vspAzimuthFactor_anchor_elevated = 0.05; compressionAngleFactor = cosd(abs(hrtf_elevations(i))); compressionAngleFactor = (compressionAngleFactor - cosd(hrtfComp_el2compress)) * ... ((hrtfComp_vspAzimuthFactor_anchor_horizontal - hrtfComp_vspAzimuthFactor_anchor_elevated) / ... (1 - cosd(hrtfComp_el2compress))) + hrtfComp_vspAzimuthFactor_anchor_elevated; compressionCenterOffset can define, for example, an elevation-dependent offset that is applied when the azimuth of the current HRTF is 0°. compressionCenterOffset can, for example, be at a minimum when elevation=0°. This ensures a compression ratio close to 0.0, which corresponds to a high level of compression and therefore a very clean timbre for important signals such as speech. As the elevation increases, compressionCenterOffset is gradually increased, for example weighted by a sine function, up to a defined maximum value. If the azimuth is not equal to 0°, compressionCenterOffset is set to 0.0. %centre offset hrtfComp_centerOffset_anchor_horizontal = 0.10; hrtfComp_centerOffset_anchor_elevated = 1.00; compressionCenterOffset = sind(abs(hrtf_elevations(i))); compressionCenterOffset = compressionCenterOffset * ... ((hrtfComp_centerOffset_anchor_elevated - hrtfComp_centerOffset_anchor_horizontal) / ... sind(hrtfComp_el2compress)) + hrtfComp_centerOffset_anchor_horizontal;

[0082] In one embodiment, compressionCenterOffset is applied to avoid, for example, compression2apply being equal to 0.0 for azimuth==0°. Additionally, compressionCenterOffset is sinusoidally weighted by elevation to ensure that the total compression applied to the central source decreases as elevation increases. A sine function can be used to calculate a value between 0.0 and 1.0, for example, by applying a sine function sin(abs(elevation)). As a result, a very clean timbre is preserved for the horizontal central source, while elevation and externalization cues are still preserved.

[0083] By applying the described algorithm, an angle-dependent band compression factor is calculated, which is shown in FIG. 3 for different compressionAngleFactor values ​​before applying compressionCenterOffset.

[0084] In particular, FIG. 3 illustrates compression for different compressionAngleFactor values ​​without applying compressionCenterOffset according to one embodiment.

[0085] The plots represent different compressionAngleFactor values ​​(and therefore different elevation angles). When compressionAngleFactor is greater than 0, compression of frontal sources increases. In particular, a compressionAngleFactor of 0 is represented by line 2000, a compressionAngleFactor of 0.25 is represented by line 2025, a compressionAngleFactor of 0.5 is represented by line 2050, a compressionAngleFactor of 0.75 is represented by line 2075, and a compressionAngleFactor of 1 is represented by line 2100.

[0086] As compressionAngleFactor is increased, frontal sound sources will be compressed more (more strongly).

[0087] Without compressionCenterOffset, at azimuth=0.0, compression2apply=0.0 will always be the case. This may not be desirable, since for example 100% compression would destroy all elevation cues and externalization.

[0088] In one embodiment, the compressionCenterOffset is applied to overcome this problem. For example, the compressionCenterOffset is minimized when the elevation angle is equal to 0, achieving a very clean timbre for important signals such as speech. As the elevation increases, the compressionCenterOffset can be gradually increased, for example weighted by a sine function, to a maximum value, for example a maximum value defined by the code.

[0089] The effect of applying compressionCenterOffset is shown in Figure 4. In particular, Figure 4 shows the effect of compressionCenterOffset on the overall compression value according to one embodiment.

[0090] According to some embodiments, a final compression ratio may be applied to, for example, the HRTFs.

[0091] For example, the final compression ratio can be applied to the HRTFs, for example, by calculating the RMS (Root Mean Square) of the uncompressed HRTF, for example, by calculating the RMS for each single HRTF separately for the left / right ear. This RMS value can serve as a pivot point, for example, across all frequencies. A flat line across frequency results. Calculating the RMS separately for the left and right ear ensures that the overall ILD (Interaural Level Difference) is preserved after compression.

[0092] In the most extreme case (100% compression), the magnitude of all frequency bins are set to the same RMS value (a flat line across frequency), resulting in a passive downmix. This has a very similar effect to vsp 0 processing (vsp=virtual speaker position), except that the original energy of the HRTF is preserved.

[0093] Then, for each QMF domain frequency band, a weighted version of the difference between the RMS and the magnitude of the uncompressed HRTF (weighted by the corresponding per-band compression ratio) can be added to, for example, the RMS. For example, for each frequency, a weighted version of the difference between the RMS and the magnitude of the uncompressed HRTF can be added to, for example, the RMS.

[0094] For example, for the frequency bands b, b=0...63, For all azimuth angles az, For all elevation angles ele, the following formula can be used: HRTF compressed (az, ele, b) = rms (HRTF uncompressed ) + + ((HRTF uncompressed (az, ele, b) -rms (HRTF uncompressed )) · · compressionFactor (az, ele, b)) HRTF compressed denotes the compressed HRTF. HRTFin compressed denotes the uncompressed HRTF. rms indicates the root mean square.

[0095] For example, the compression ratio (az,ele,0) may, for example, always be equal to 0.25 across all azimuth and elevation angles.

[0096] This means that if compressionFactor is equal to 0.0 (fully compressed), the output HRTF can be, for example, the RMS of the input HRTF. If compressionFactor is equal to, for example, 0.5 (50% compression), a portion of the uncompressed HRTF is brought back to the RMS in a frequency-dependent manner.

[0097] For example, in one embodiment, the rendering information processor 110 may, for example, compressed By using the above equation for , or by using a different equation, an HRTF compression stage can be provided which provides a means of moving smoothly between these two states of "uncompressed" and "fully compressed."

[0098] FIG. 5 is a diagram illustrating an overall HRTF compression process according to one embodiment. In one embodiment, by employing the above concepts, a means for individual (per user) HRTF personalization is provided. According to one embodiment, different compression presets may be provided to the user for example to choose from. In one embodiment, the user may individually adjust the HRTF compression to their preferences.

[0099] Further embodiments are provided below. According to one embodiment, compression may for example be applied in a different frequency domain, for example in the FFT domain rather than the QMF domain.

[0100] In one embodiment, the processing of the lowest frequency band may, for example, be done in a different way: for example, a dynamic algorithm may start operating in band 0 instead of band 1, or a different predefined fixed compression value for the lowest band may be used.

[0101] According to one embodiment, the application of the angle-dependent compression factor may, for example, be limited to a different range of frequency bands (eg, starting with band 2 instead of band 1, or only running up to band 48).

[0102] In some embodiments, functions other than cosine or sine functions can be used, for example to define a linear function of the angle-dependent parameter, for example a quadratic function.

[0103] According to one embodiment, the orientation of the weighting pattern of the angular coefficients may be rotated such that, for example, a high level of compression is instead applied to rear sound sources, while frontal sound sources are hardly compressed at all.

[0104] In some embodiments, varying amounts of compression across different frequency regions can be used, for example to preserve elevated HRTF elevation cues at higher frequencies. Further embodiments are provided below. Embodiment 1: An apparatus, comprising: a rendering information processor (110) configured to modify the original binaural rendering information in dependence on the directional information to obtain modified binaural rendering information in which the spectral distortion is adjusted; An apparatus comprising: Embodiment 2: The rendering information processor (110) is configured to modify the original binaural rendering information such that a degree of adjustment of the spectral distortion depends on the directional information. 2. The device of embodiment 1. Embodiment 3: The binaural rendering information is suitable for being used to process one or more audio input signals to obtain a binaural signal including two audio channels; 3. The device of embodiment 1 or 2. Embodiment 4: The apparatus further comprises a signal processor (120) configured to process the one or more audio input signals depending on the modified binaural rendering information to obtain the binaural signal including the two audio channels. 4. The device of embodiment 3. Embodiment 5: The original binaural rendering information includes one or more original head-related transfer function pairs, each of the one or more original head-related transfer function pairs including a first original head-related transfer function and a second original head-related transfer function; dependent on the directional information, the rendering information processor (110) is configured to modify the first original head-related transfer function and / or the second original head-related transfer function of each of the one or more original head-related transfer function pairs to obtain a first modified head-related transfer function and / or a second modified head-related transfer function of each of the one or more modified head-related transfer function pairs. 5. A device according to any one of embodiments 1 to 4. Embodiment 6: The rendering information processor (110) determines a coefficient depending on a direction, the rendering information processor (110) is configured to apply coefficients to at least one first original head-related transfer function and / or a second original head-related transfer function of the one or more original head-related transfer function pairs to obtain at least one first modified head-related transfer function and / or a second modified head-related transfer function of the one or more modified head-related transfer function pairs; 6. The device of embodiment 5. Embodiment 7: The coefficient is a compression ratio. 7. The device of embodiment 6. Embodiment 8: The signal processor (120) is configured to process the one or more audio input signals in dependence on at least one modified head-related transfer function pair of the one or more modified head-related transfer function pairs to obtain the binaural signal. The device according to any one of embodiments 5 to 7, which is further dependent on embodiment 4. Embodiment 9: Each of the first original head-related transfer function and the second original head-related transfer function of each of the one or more original head-related transfer function pairs and each of the first modified head-related transfer function and the second modified head-related transfer function of each of the one or more modified head-related transfer function pairs is a head-related transfer function, or a head-related impulse response, or a binaural room transfer function, or a binaural room impulse response. 9. A device according to any one of embodiments 5 to 8. Embodiment 10: The rendering information processor (110) is configured to process the first original head-related transfer function and / or the second original head-related transfer function of each of one or more head-related transfer function pairs in the frequency domain. 10. A device according to any one of embodiments 5 to 9. Embodiment 11: The rendering information processor (110) is configured to modify a first original HRTF and / or a second original HRTF of each original HRTF pair of one or more HRTF pairs in dependence on the directional information such that a magnitude spectrum of the first original HRTF and / or a magnitude spectrum of the second original HRTF of the original HRTF pair is modified. 11. A device according to any one of embodiments 5 to 10. Embodiment 12: The rendering information processor (110) is configured to modify the first original head-related transfer function and / or the second original head-related transfer function of each original head-related transfer function pair of one or more head-related transfer function pairs in dependence on the directional information such that at least one magnitude difference between two frequency bands of the first original head-related transfer function and / or the second original head-related transfer function of the original head-related transfer function pair is corrected. 12. A device according to any one of embodiments 5 to 11. Embodiment 13: If the directional information indicates that the spectral distortion should be reduced, the rendering information processor (110) is configured to modify the first original HRTF and / or the second original HRTF of each original HRTF pair of one or more HRTF pairs in dependence on the directional information such that at least one magnitude difference between two frequency bands of the first original HRTF and / or the second original HRTF of the original HRTF pair is reduced. 13. The device of embodiment 12. Embodiment 14: The directional information includes directional information for each of the one or more head-related transfer function pairs. 14. A device according to any one of embodiments 5 to 13. Embodiment 15: The directional information of each of the one or more head-related transfer function pairs includes an elevation angle and / or an azimuth angle of the head-related transfer function pair; the rendering information processor (110) is configured to modify the first original HRTF and / or the second original HRTF of the original HRTF pair depending on the elevation angle and / or the azimuth angle for the HRTF pair; 15. The device of embodiment 14. Embodiment 16: The rendering information processor (110) is configured to determine one or more modification parameters depending on the directional information, the rendering information processor (110) is configured to modify the first original head-related transfer function and / or the second original head-related transfer function of each of the one or more original head-related transfer function pairs in dependence on at least one of the one or more modification parameters; each of the one or more modification parameters indicates a degree of adjustment of the spectral distortion; 16. The device of any one of embodiments 5 to 15, further dependent on embodiment 2. Embodiment 17: The rendering information processor (110) is configured to determine the one or more correction parameters by determining at least one of the one or more correction parameters for each of the one or more head-related transfer function pairs in dependence on the elevation angle and / or in dependence on the azimuth angle of the head-related transfer function pair, each of the modification parameters of the head-related transfer function pair indicates a degree of adjustment of a spectral distortion in the first modified head-related transfer function and / or the second modified head-related transfer function of the modified head-related transfer function pair compared to a spectral distortion in the first original head-related transfer function and / or the second original head-related transfer function of the original head-related transfer function pair, The device according to embodiment 16, which is further dependent on embodiment 15. Embodiment 18: The rendering information processor (110) is configured to determine the at least one modification parameter for each of the one or more pairs of head-related transfer functions in dependence on frequency. 18. The device of embodiment 17. Embodiment 19: The rendering information processor (110) is configured to generate at least one modification parameter for each head-related transfer function pair of one or more head-related transfer function pairs such that, when the azimuth angle of the head-related transfer function pair indicates the presence of a frontal sound source, the modification parameter is generated in a different way for the same value of the elevation angle of the head-related transfer function pair compared to when the azimuth angle of the head-related transfer function pair does not indicate the presence of a frontal sound source. 19. The device of embodiment 17 or 18. Embodiment 20: The rendering information processor (110) is configured to generate the at least one correction parameter for each head-related transfer function pair of the one or more head-related transfer function pairs by generating an offset value depending on the elevation angle of the head-related transfer function pair when the azimuth angle of the head-related transfer function pair indicates the presence of the frontal sound source. 20. The device of embodiment 19. Embodiment 21: The one or more original head-related transfer function pairs are a plurality of original head-related transfer function pairs, and the directional information comprises different directional information for each of the plurality of head-related transfer function pairs; the rendering information processor (110) is configured to modify a first original head-related transfer function and / or a second original head-related transfer function of each original head-related transfer function pair of the plurality of original head-related transfer function pairs in dependence on directional information of the original head-related transfer function pair to obtain a first modified head-related transfer function and / or a second modified head-related transfer function of each of one or more modified head-related transfer function pairs, the plurality of modified head-related transfer function pairs; the signal processor (120) is configured to process the one or more audio input signals in dependence on at least one modified head-related transfer function pair of the plurality of modified head-related transfer function pairs to obtain a binaural signal; 21. The device of any one of embodiments 5 to 20, further dependent on embodiment 4.

[0036] Embodiment 22: The signal processor (120) is configured to process the one or more audio input signals in dependence on one or more pairs of interpolated head-related transfer functions to obtain the binaural signal; the rendering information processor (110) determines the interpolated head-related transfer functions including a first interpolated head-related transfer function and a second interpolated head-related transfer function; the rendering information processor (110) is configured to determine the first interpolated head-related transfer function by interpolating between the first head-related transfer function of each of at least two head-related transfer function pairs of the plurality of head-related transfer function pairs in dependence on the directional information; the rendering information processor (110) is configured to determine the second interpolated head-related transfer function by interpolating between the second head-related transfer function of each of the at least two head-related transfer function pairs of the plurality of head-related transfer function pairs in dependence on the directional information. 22. The device of embodiment 21. Embodiment 23: In order to modify the original binaural rendering information in dependence on the direction information to obtain the modified binaural rendering information in which the spectral distortion is adjusted, the rendering information processor (110) is configured to use the following formula: HRTF compressed (az, ele, b) = rms (HRTF uncompressed ) + + ((HRTF uncompressed (az, ele, b) -rms (HRTF uncompressed )) · · compressionFactor (az, ele, b)) In the formula, b represents a frequency band, az indicates the azimuth angle, ele indicates the elevation angle, HRTF compressed denotes the compressed HRTF, HRTF uncompressed denotes the uncompressed HRTF, rms stands for root mean square, 23. A device according to any one of embodiments 1 to 22. Embodiment 24: A method, comprising: Modifying the original binaural rendering information to obtain modified binaural rendering information in which the spectral distortion is adjusted depending on the directional information. A method comprising: Embodiment 25: A computer program for carrying out the method according to embodiment 24 when executed on a computer or signal processor.

[0105] Although some aspects are described in the context of an apparatus, it will be apparent that these aspects also represent a description of a corresponding method, with blocks or devices corresponding to method steps or features of method steps. Similarly, aspects described in the context of a method step also represent a description of the corresponding block or item or feature of the corresponding apparatus. Some or all of the method steps may be performed by (or using) a hardware apparatus, such as, for example, a microprocessor, a programmable computer, or an electronic circuit. In some embodiments, one or more of the most important method steps may be performed by such an apparatus.

[0106] Depending on the specific implementation requirements, the embodiments of the present invention can be implemented in hardware or software, or at least partly in hardware, or at least partly in software. The embodiments can be implemented using a digital storage medium, such as, for example, a floppy disk, DVD, Blu-ray, CD, ROM, PROM, EPROM, EEPROM or flash memory, having electronically readable control signals stored therein and cooperating (or capable of cooperating) with a programmable computer system such that the respective methods are performed. Thus, the digital storage medium may be computer readable.

[0107] Some embodiments according to the invention comprise a data carrier having electronically readable control signals which cooperate with a programmable computer system to perform one of the methods described herein.

[0108] Generally, embodiments of the present invention may be implemented as a computer program product having a program code operative to perform one of the methods when the computer program product runs on a computer. The program code may for example be stored on a machine readable carrier.

[0109] Other embodiments comprise the computer program for performing one of the methods described herein, stored on a machine readable carrier.

[0110] In other words, an embodiment of the inventive method is, therefore, a computer program having a program code for performing one of the methods described herein, when the computer program runs on a computer.

[0111] A further embodiment of the inventive method is therefore a data carrier (or digital storage medium or computer readable medium) comprising, and recorded thereon, the computer program for performing one of the methods described herein. The data carrier, digital storage medium or recording medium is typically tangible and / or non-transitory.

[0112] A further embodiment of the inventive method is therefore a data stream or a sequence of signals representing the computer program for performing one of the methods described herein. The data stream or the sequence of signals can for example be arranged to be transferred via a data communication connection, for example the Internet.

[0113] A further embodiment comprises a processing means, for example a computer, or a programmable logic device, configured to or adapted to perform one of the methods described herein.

[0114] A further embodiment comprises a computer having installed thereon the computer program for performing one of the methods described herein.

[0115] Further embodiments according to the invention include an apparatus or system configured to transfer (e.g. electronically or optically) a computer program for performing one of the methods described herein to a receiver. The receiver may be, for example, a computer, a mobile device, a memory device, etc. The apparatus or system may, for example, comprise a file server for transferring the computer program to the receiver.

[0116] In some embodiments, a programmable logic device (e.g., a field programmable gate array) may be used to perform some or all of the functions of the methods described herein. In some embodiments, a field programmable gate array may cooperate with a microprocessor to perform one of the methods described herein. In general, the methods are preferably performed by any hardware apparatus.

[0117] The apparatus described herein may be implemented using a hardware apparatus, or using a computer, or using a combination of a hardware apparatus and a computer.

[0118] The methods described herein may be performed using a hardware apparatus, or using a computer, or using a combination of a hardware apparatus and a computer.

[0119] The above-described embodiments are merely illustrative of the principles of the present invention. It is understood that modifications and variations of the configurations and details described herein are obvious to those skilled in the art. It is therefore intended to be limited only by the scope of the appended claims, and not by the specific details shown by the description and illustration of the embodiments herein.

[0120] literature [1] Merimaa, J.: “Modification of HRTF filters to reduce timbral effects in binaural synthesis”, In Audio Engineering Society Convention 127. Audio Engineering Society, 2009. [2] Merimaa, J.: “Modification of HRTF filters to reduce timbral effects in binaural synthesis, part 2: Individual HRTFs”, In Audio Engineering Society Convention 129, 2010. [3] Song Li: “On Externalization of Virtual Sound Images Presented via Headphones”, PhD Thesis University Hannover, 2021, (Experiment D). [4] DE 10 2019 135 690 A1, Pellegrini, “Verfahren und Vorrichtung zur Audiosignalverarbeitung fuer binaurale Virtualisierung“. [5] US 2021 0195361 A1, Pellegrini, “Method and device for audio signal processing for binaural virtualization”. [6] Marentakis, G. and Hoelzl, J.: “Compression Efficiency and Signal Distortion of Common PCA Bases for HRTF Modelling” 18th Sound and Music Computing Conference (SMC 2021), Virtual, 29 June - 01 July 2021. [7] Hoelzl, J.: “An initial Investigation into HRTF Adaptation using PCA”. [8] Lin Wang: “HRTF Compression via Principal Components Analysis and Vector Quantization”, 2008. [9] Jing Wang: “Compression of Head-Related Transfer Function Based on Tucker and Tensor Train Decomposition”, 2019.

Claims

1. An apparatus, comprising: a rendering information processor (110) configured to modify the original binaural rendering information in dependence on the directional information to obtain modified binaural rendering information with adjusted spectral distortion; An apparatus comprising:

2. the rendering information processor (110) is configured to modify the original binaural rendering information such that a degree of adjustment of the spectral distortion depends on the directional information.

2. The apparatus of claim 1.

3. the binaural rendering information is suitable to be used for processing one or more audio input signals to obtain a binaural signal comprising two audio channels.

3. Apparatus according to claim 1 or 2.

4. the apparatus further comprises a signal processor (120) configured to process the one or more audio input signals in dependence on the modified binaural rendering information to obtain the binaural signal comprising the two audio channels.

4. The apparatus of claim 3.

5. the original binaural rendering information comprises one or more original head-related transfer function pairs, each of the one or more original head-related transfer function pairs comprising a first original head-related transfer function and a second original head-related transfer function; dependent on the directional information, the rendering information processor (110) is configured to modify the first original head-related transfer function and / or the second original head-related transfer function of each of the one or more original head-related transfer function pairs to obtain a first modified head-related transfer function and / or a second modified head-related transfer function of each of one or more modified head-related transfer function pairs.

5. Apparatus according to any one of claims 1 to 4.

6. The rendering information processor (110) determines coefficients depending on the direction; the rendering information processor (110) is configured to apply the coefficients to the first original head-related transfer function and / or the second original head-related transfer function of at least one of the one or more original head-related transfer function pairs to obtain the first modified head-related transfer function and / or the second modified head-related transfer function of at least one of the one or more modified head-related transfer function pairs.

6. The apparatus of claim 5.

7. The coefficient is the compression ratio.

7. The apparatus of claim 6.

8. the signal processor (120) is configured to process the one or more audio input signals in dependence on at least one modified head-related transfer function pair of the one or more modified head-related transfer function pairs to obtain the binaural signal. Apparatus according to any one of claims 5 to 7, further dependent on claim 4.

9. each of the first original head-related transfer function and the second original head-related transfer function of each of the one or more original head-related transfer function pairs and each of the first modified head-related transfer function and the second modified head-related transfer function of the one or more modified head-related transfer function pairs is a head-related transfer function, or a head-related impulse response, or a binaural room transfer function, or a binaural room impulse response; 9. Apparatus according to any one of claims 5 to 8.

10. the rendering information processor (110) is configured to process the first original head-related transfer function and / or the second original head-related transfer function of each of the one or more head-related transfer function pairs in a frequency domain; 10. Apparatus according to any one of claims 5 to 9.

11. the rendering information processor (110) is configured to modify the first original HRTF and / or the second original HRTF of each original HRTF pair of the one or more HRTF pairs in dependence on the directional information such that a magnitude spectrum of the first original HRTF and / or a magnitude spectrum of the second original HRTF of the original HRTF pair is modified, 11. Apparatus according to any one of claims 5 to 10.

12. the rendering information processor (110) is configured to modify the first original head-related transfer function and / or the second original head-related transfer function of each original head-related transfer function pair of the one or more head-related transfer function pairs in dependence on the directional information such that at least one magnitude difference between two frequency bands of the first original head-related transfer function and / or the second original head-related transfer function of the original head-related transfer function pair is corrected, 12. Apparatus according to any one of claims 5 to 11.

13. if the directional information indicates that a spectral distortion should be reduced, the rendering information processor (110) is configured to modify the first original HRTF and / or the second original HRTF of each original HRTF pair of the one or more HRTF pairs in dependence on the directional information such that at least one magnitude difference between two frequency bands of the first original HRTF and / or the second original HRTF of the original HRTF pair is reduced.

13. The apparatus of claim 12.

14. The directional information includes directional information of each of the one or more head related transfer function pairs.

14. Apparatus according to any one of claims 5 to 13.

15. the directional information of each of the one or more head-related transfer function pairs includes an elevation angle and / or an azimuth angle of the head-related transfer function pair; the rendering information processor (110) is configured to modify the first original HRTF and / or the second original HRTF of the original HRTF pair in dependence on the elevation angle and / or the azimuth angle for the HRTF pair, 15. The apparatus of claim 14.

16. the rendering information processor (110) is configured to determine one or more modification parameters in dependence on the directional information; the rendering information processor (110) is configured to modify the first original head-related transfer function and / or the second original head-related transfer function of each of the one or more original head-related transfer function pairs in dependence on the at least one of the one or more modification parameters; each of the one or more modification parameters indicative of the degree of the adjustment of the spectral distortion. Apparatus according to any one of claims 5 to 15, further dependent on claim 2.

17. the rendering information processor (110) is configured to determine the one or more modification parameters by determining at least one of the one or more modification parameters for each of the one or more head-related transfer function pairs in dependence on the elevation angle and / or in dependence on the azimuth angle of the head-related transfer function pairs, each of the modification parameters of the head-related transfer function pair indicates the degree of adjustment of the spectral distortion in the first modified head-related transfer function and / or the second modified head-related transfer function of the modified head-related transfer function pair compared to the spectral distortion in the first original head-related transfer function and / or the second original head-related transfer function of the original head-related transfer function pair, 17. Apparatus according to claim 16, further dependent on claim 15.

18. the rendering information processor (110) is configured to determine the at least one modification parameter for each of the one or more pairs of head-related transfer functions in dependence on frequency; 20. The apparatus of claim 17.

19. the rendering information processor (110) is configured to generate the at least one modification parameter for each head-related transfer function pair of the one or more head-related transfer function pairs such that, when the azimuth angle of the head-related transfer function pair indicates the presence of a frontal sound source, the modification parameter is generated in a different way for the same value of the elevation angle of the head-related transfer function pair compared to when the azimuth angle of the head-related transfer function pair does not indicate the presence of a frontal sound source.

19. Apparatus according to claim 17 or 18.

20. the rendering information processor (110) is configured to generate the at least one modification parameter for each head-related transfer function pair of the one or more head-related transfer function pairs by generating an offset value depending on the elevation angle of the head-related transfer function pair if the azimuth angle of the head-related transfer function pair indicates the presence of the frontal sound source.

20. The apparatus of claim 19.

21. the one or more original head-related transfer function pairs are a plurality of original head-related transfer function pairs, and the directional information comprises different directional information for each of the plurality of head-related transfer function pairs; the rendering information processor (110) is configured to modify the first original head-related transfer function and / or the second original head-related transfer function of each original head-related transfer function pair of the plurality of original head-related transfer function pairs in dependence on the directional information of the original head-related transfer function pair to obtain a first modified head-related transfer function and / or a second modified head-related transfer function of each of the one or more modified head-related transfer function pairs, the first modified head-related transfer function and / or the second modified head-related transfer function of each of the one or more modified head-related transfer function pairs being a plurality of modified head-related transfer function pairs; the signal processor (120) is configured to process the one or more audio input signals in dependence on the at least one modified head-related transfer function pair of the plurality of modified head-related transfer function pairs to obtain the binaural signal. Apparatus according to any one of claims 5 to 20, further dependent on claim 4.

22. the signal processor (120) is configured to process the one or more audio input signals in dependence on one or more pairs of interpolated head-related transfer functions to obtain the binaural signal; The rendering information processor (110) determines the interpolated head-related transfer functions including a first interpolated head-related transfer function and a second interpolated head-related transfer function; the rendering information processor (110) is configured to determine the first interpolated head-related transfer function by interpolating between the first head-related transfer function of each of at least two head-related transfer function pairs of the plurality of head-related transfer function pairs in dependence on the directional information; the rendering information processor (110) is configured to determine the second interpolated head-related transfer function by interpolating between the second head-related transfer function of each of the at least two head-related transfer function pairs of the plurality of head-related transfer function pairs in dependence on the directional information.

22. The apparatus of claim 21.

23. In order to modify the original binaural rendering information in dependence on the direction information to obtain the modified binaural rendering information in which the spectral distortion has been adjusted, the rendering information processor (110) is configured to use the following formula: HRTF compressed (a-z, e-l, b)=rms(HRTF) uncompressed , + (( HRTF uncompressed (az,ele,b)-rms (HRTF uncompressed , ・ compressionFactor (az, ele, b)) In the formula, b represents a frequency band, az indicates the azimuth angle, ele indicates the elevation angle, HRTF ｃｏｍｐｒｅｓｓｅｄ denotes the compressed HRTF, HRTF ｕｎｃｏｍｐｒｅｓｓｅｄ denotes uncompressed HRTF, rms stands for root mean square 23. Apparatus according to any one of claims 1 to 22.

24. 1. A method, comprising: Modifying the original binaural rendering information to obtain modified binaural rendering information in which the spectral distortion is adjusted depending on the directional information. A method comprising:

25. 25. A computer program for carrying out the method according to claim 24 when executed on a computer or signal processor.

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