Patent Publication Number: US-10313815-B2

Title: Apparatus and method for generating a plurality of parametric audio streams and apparatus and method for generating a plurality of loudspeaker signals

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of copending International Application No. PCT/EP2013/073574, filed Nov. 12, 2013, which is incorporated herein by reference in its entirety, and additionally claims priority from U.S. Application No. 61/726,887, filed Nov. 15, 2012, and European Application No. 13159421.0, filed Mar. 15, 2013, both of which are also incorporated herein by reference in their entirety. 
    
    
     The present invention generally relates to a parametric spatial audio processing, and in particular to an apparatus and a method for generating a plurality of parametric audio streams and an apparatus and a method for generating a plurality of loudspeaker signals. Further embodiments of the present invention relate to a sector-based parametric spatial audio processing. 
     BACKGROUND OF THE INVENTION 
     In multichannel listening, the listener is surrounded with multiple loudspeakers. A variety of known methods exist to capture audio for such setups. Let us first consider loudspeaker systems and the spatial impression that can be created with them. Without special techniques, common two-channel stereophonic setups can only create auditory events on the line connecting the loudspeakers. Sound emanating from other directions cannot be produced. Logically, by using more loudspeakers around the listener, more directions can be covered and a more natural spatial impression can be created. The most well known multichannel loudspeaker system and layout is the 5.1 standard (“ITU-R 775-1”), which consists of five loudspeakers at azimuthal angles of 0°, 30° and 110° with respect to the listening position. Other systems with a varying number of loudspeakers located at different directions are also known. 
     In the art, several different recording methods have been designed for the previously mentioned loudspeaker systems, in order to reproduce the spatial impression in the listening situation as it would be perceived in the recording environment. The ideal way to record spatial sound for a chosen multichannel loudspeaker system would be to use the same number of microphones as there are loudspeakers. In such a case, the directivity patterns of the microphones should also correspond to the loudspeaker layout such that sound from any single direction would only be recorded with one, two, or three microphones. The more loudspeakers are used, the narrower directivity patterns are thus needed. However, such narrow directional microphones are relatively expensive, and have typically a non-flat frequency response, which is not desired. Furthermore, using several microphones with too broad directivity patterns as input to multichannel reproduction results in a colored and blurred auditory perception, due to the fact that sound emanating from a single direction is usually reproduced with more loudspeakers than is useful. Hence, current microphones are best suited for two-channel recording and reproduction without the goal of a surrounding spatial impression. 
     Another known approach to spatial sound recording is to record a large number of microphones which are distributed over a wide spatial area. For example, when recording an orchestra on a stage, the single instruments can be picked up by so-called spot microphones, which are positioned closely to the sound sources. The spatial distribution of the frontal sound stage can, for example, be captured by conventional stereo microphones. The sound field components corresponding to the late reverberation can be captured by several microphones placed at a relatively far distance to the stage. A sound engineer can then mix the desired multichannel output by using a combination of all microphone channels available. However, this recording technique implies a very large recording setup and hand crafted mixing of the recorded channels, which is not always feasible in practice. 
     Conventional systems for the recording and reproduction of spatial audio based on directional audio coding (DirAC), as described in T. Lokki, J. Merimaa, V. Pulkki: Method for Reproducing Natural or Modified Spatial Impression in Multichannel Listening, U.S. Pat. No. 7,787,638 B2, Aug. 31, 2010 and V. Pulkki: Spatial Sound Reproduction with Directional Audio Coding. J. Audio Eng. Soc., Vol. 55, No. 6, pp. 503-516, 2007, rely on a simple global model for the sound field. Therefore, they suffer from some systematic drawbacks, which limits the achievable sound quality and experience in practice. 
     A general problem of known solutions is that they are relatively complex and typically associated with a degradation of the spatial sound quality. 
     SUMMARY 
     According to an embodiment, an apparatus for generating a plurality of parametric audio streams from an input spatial audio signal acquired from a recording in a recording space may have: a segmentor for generating at least two input segmental audio signals from the input spatial audio signal; wherein the segmentor is configured to generate the at least two input segmental audio signals depending on corresponding segments of the recording space, wherein the segments of the recording space each represent a subset of directions within a two-dimensional plane or within a three-dimensional space, and wherein the segments are different from each other; and a generator for generating a parametric audio stream for each of the at least two input segmental audio signals to acquire the plurality of parametric audio streams, so that the plurality of parametric audio streams each include a component of the at least two input segmental audio signals and a corresponding parametric spatial information, wherein the parametric spatial information of each of the parametric audio steams includes direction-of-arrival parameter and/or a diffuseness parameter. 
     According to another embodiment, an apparatus for generating a plurality of loudspeaker signals from a plurality of parametric audio streams; wherein each of the plurality of parametric audio streams includes a segmental audio component and a corresponding parametric spatial information; wherein the parametric spatial information of each of the parametric audio steams includes a direction-of-arrival parameter and/or a diffuseness parameter; may have: a renderer for providing a plurality of input segmental loudspeaker signals from the plurality of parametric audio streams, so that the input segmental loudspeaker signals depend on corresponding segments of a recording space, wherein the segments of the recording space each represent a subset of directions within a two-dimensional plane or within a three-dimensional space, and wherein the segments are different from each other; wherein the renderer is configured for rendering each of the segmental audio components using the corresponding parametric spatial information to acquire the plurality of input segmental loudspeaker signals; and a combiner for combining the input segmental loudspeaker signals to acquire the plurality of loudspeaker signals. 
     According to another embodiment, a method for generating a plurality of parametric audio streams from an input spatial audio signal acquired from a recording in a recording space may have the steps of: generating at least two input segmental audio signals from the input spatial audio signal; wherein generating the at least two input segmental audio signals is conducted depending on corresponding segments of the recording space, wherein the segments of the recording space each represent a subset of directions within a two-dimensional plane or within a three-dimensional space, and wherein the segments are different from each other; generating a parametric audio stream for each of the at least two input segmental audio signals to acquire the plurality of parametric audio streams, so that the plurality of parametric audio streams each include a component of the at least two input segmental audio signals and a corresponding parametric spatial information, wherein the parametric spatial information of each of the parametric audio steams includes direction-of-arrival parameter and/or a diffuseness parameter. 
     According to another embodiment, a method for generating a plurality of loudspeaker signals from a plurality of parametric audio streams; wherein each of the plurality of parametric audio streams includes a segmental audio component and a corresponding parametric spatial information; wherein the parametric spatial information of each of the parametric audio steams includes a direction-of-arrival parameter and/or a diffuseness parameter; may have the steps of: providing a plurality of input segmental loudspeaker signals from the plurality of parametric audio streams, so that the input segmental loudspeaker signals depend on corresponding segments of a recording space, wherein the segments of the recording space each represent a subset of directions within a two-dimensional plane or within a three-dimensional space, and wherein the segments are different from each other; wherein providing the plurality of input segmental loudspeaker signals is conducted by rendering each of the segmental audio components using the corresponding parametric spatial information to acquire the plurality of input segmental loudspeaker signals; and combining the input segmental loudspeaker signals to acquire the plurality of loudspeaker signals. 
     According to another embodiment, a computer program including a program code for performing the method according to claim  11  when the computer program is executed on a computer. 
     According to another embodiment, a computer program including a program code for performing the method according to claim  12  when the computer program is executed on a computer. 
     The basic idea underlying the present invention is that the improved parametric spatial audio processing can be achieved if at least two input segmental audio signals are provided from the input spatial audio signal, wherein the at least two input segmental audio signals are associated with corresponding segments of the recording space, and if a parametric audio stream is generated for each of the at least two input segmental audio signals to obtain the plurality of parametric audio streams. This allows to achieve the higher quality, more realistic spatial sound recording and reproduction using relatively simple and compact microphone configurations. 
     According to a further embodiment, the segmentor is configured to use a directivity pattern for each of the segments of the recording space. Here, the directivity pattern indicates a directivity of the at least two input segmental audio signals. By the use of the directivity patterns, it is possible to obtain a better model match of the observed sound field, especially in complex sound scenes. 
     According to a further embodiment, the generator is configured for obtaining the plurality of parametric audio streams, wherein the plurality of parametric audio streams each comprise a component of the at least two input segmental audio signals and a corresponding parametric spatial information. For example, the parametric spatial information of each of the parametric audio streams comprises a direction-of-arrival (DOA) parameter and/or a diffuseness parameter. By providing the DOA parameters and/or the diffuseness parameters, it is possible to describe the observed sound field in a parametric signal representation domain. 
     According to a further embodiment, an apparatus for generating a plurality of loudspeaker signals from a plurality of parametric audio streams derived from an input spatial audio signal recorded in a recording space comprises a renderer and a combiner. The renderer is configured for providing a plurality of input segmental loudspeaker signals from the plurality of parametric audio streams. Here, the input segmental loudspeaker signals are associated with corresponding segments of the recording space. The combiner is configured for combining the input segmental loudspeaker signals to obtain the plurality of loudspeaker signals. 
     Further embodiments of the present invention provide methods for generating a plurality of parametric audio streams and for generating a plurality of loudspeaker signals. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will be detailed subsequently referring to the appended drawings, in which: 
         FIG. 1  shows a block diagram of an embodiment of an apparatus for generating a plurality of parametric audio streams from an input spatial audio signal recording in a recording space with a segmentor and a generator; 
         FIG. 2  shows a schematic illustration of the segmentor of the embodiment of the apparatus in accordance with  FIG. 1  based on a mixing or matrixing operation; 
         FIG. 3  shows a schematic illustration of the segmentor of the embodiment of the apparatus in accordance with  FIG. 1  using a directivity pattern; 
         FIG. 4  shows a schematic illustration of the generator of the embodiment of the apparatus in accordance with  FIG. 1  based on a parametric spatial analysis; 
         FIG. 5  shows a block diagram of an embodiment of an apparatus for generating a plurality of loudspeaker signals from a plurality of parametric audio streams with a renderer and a combiner; 
         FIG. 6  shows a schematic illustration of example segments of a recording space, each representing a subset of directions within a two-dimensional (2D) plane or within a three-dimensional (3D) space; 
         FIG. 7  shows a schematic illustration of an example loudspeaker signal computation for two segments or sectors of a recording space; 
         FIG. 8  shows a schematic illustration of an example loudspeaker signal computation for two segments or sectors of a recording space using second order B-format input signals; 
         FIG. 9  shows a schematic illustration of an example loudspeaker signal computation for two segments or sectors of a recording space including a signal modification in a parametric signal representation domain; 
         FIG. 10  shows a schematic illustration of example polar patterns of input segmental audio signals provided by the segmentor of the embodiment of the apparatus in accordance with  FIG. 1 ; 
         FIG. 11  shows a schematic illustration of an example microphone configuration for performing a sound field recording; and 
         FIG. 12  shows a schematic illustration of an example circular array of omnidirectional microphones for obtaining higher order microphone signals. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Before discussing the present invention in further detail using the drawings, it is pointed out that in the figures identical elements, elements having the same function or the same effect are provided with the same reference numerals so that the description of these elements and the functionality thereof illustrated in the different embodiments is mutually exchangeable or may be applied to one another in the different embodiments. 
       FIG. 1  shows a block diagram of an embodiment of an apparatus  100  for generating a plurality of parametric audio streams  125  (θ i , Ψ i , W i ) from an input spatial audio signal  105  obtained from a recording in a recording space with a segmentor  110  and a generator  120 . For example, the input spatial audio signal  105  comprises an omnidirectional signal W and a plurality of different directional signals X, Y, Z, U, V (or X, Y, U, V). As shown in  FIG. 1 , the apparatus  100  comprises a segmentor  110  and a generator  120 . For example, the segmentor  110  is configured for providing at least two input segmental audio signals  115  (W i , X i , Y i , Z i ) from the omnidirectional signal W and the plurality of different directional signals X, Y, Z, U, V of the input spatial audio signal  105 , wherein the at least two input segmental audio signals  115  (W i , X i , Y i , Z i ) are associated with corresponding segments Seg i  of the recording space. Furthermore, the generator  120  may be configured for generating a parametric audio stream for each of the at least two input segmentor audio signals  115  (W i , X i , Y i , Z i ) to obtain the plurality of parametric audio streams  125  (θ i , Ψ i , W i ). 
     By the apparatus  100  for generating the plurality of parametric audio streams  125 , it is possible to avoid a degradation of the spatial sound quality and to avoid relatively complex microphone configurations. Accordingly, the embodiment of the apparatus  100  in accordance with  FIG. 1  allows for a higher quality, more realistic spatial sound recording using relatively simple and compact microphone configurations. 
     In embodiments, the segments Seg i  of the recording space each represent a subset of directions within a two-dimensional (2D) plane or within a three-dimensional (3D) space. 
     In embodiments, the segments Seg i  of the recording space each are characterized by an associated directional measure. 
     According to embodiments, the apparatus  100  is configured for performing a sound field recording to obtain the input spatial audio signal  105 . For example, the segmentor  110  is configured to divide a full angle range of interest into the segments Seg i  of the recording space. Furthermore, the segments Seg i  of the recording space may each cover a reduced angle range compared to the full angle range of interest. 
       FIG. 2  shows a schematic illustration of the segmentor  110  of the embodiment of the apparatus  100  in accordance with  FIG. 1  based on a mixing (or matrixing) operation. As exemplarily depicted in  FIG. 2 , the segmentor  110  is configured to generate the at least two input segmental audio signals  115  (W i , X i , Y i , Z i ) from the omnidirectional signal W and the plurality of different directional signals X, Y, Z, U, V using a mixing or matrixing operation which depends on the segments Seg i  of the recording space. By the segmentor  110  exemplarily shown in  FIG. 2 , it is possible to map the omnidirectional signal W and the plurality of different directional signals X, Y, Z, U, V constituting the input spatial audio signal  105  to the at least two input segmental audio signal  115  (W i , X i , Y i , Z i ) using a predefined mixing or matrixing operation. This predefined mixing or matrixing operation depends on the segments Seg i  of the recording space and can substantially be used to branch off the at least two input segmental audio signals  115  (W i , X i , Y i , Z i ) from the input spatial audio signal  105 . The branching off of the at least two input segmental audio signals  115  (W i , X i , Y i , Z i ) by the segmentor  110  which is based on the mixing or matrixing operation substantially allows to achieve the above mentioned advantages as opposed to a simple global model for the sound field. 
       FIG. 3  shows a schematic illustration of the segmentor  110  of the embodiment of the apparatus  100  in accordance with  FIG. 1  using a (desired or predetermined) directivity pattern  305 , q i (ϑ). As exemplarily depicted in  FIG. 3 , the segmentor  110  is configured to use a directivity pattern  305 , q i (ϑ) for each of the segments Seg i  of the recording space. Furthermore, the directivity pattern  305 , q i (ϑ), may indicate a directivity of the at least two input segmental audio signals  115  (W i , X i , Y i , Z i ). 
     In embodiments, the directivity pattern  305 , q i (ϑ), is given by
 
 q   i (ϑ)= a+b  cos(ϑ+Θ i )  (1)
 
where a and b denote multipliers that can be modified to obtain desired directivity patterns and wherein ϑ denotes an azimuthal angle and Θ i  indicates an advantageous direction of the i&#39;th segment of the recording space. For example, a lies in a range of 0 to 1 and b in a range of −1 to 1.
 
     One useful choice of multipliers a, b may be a=0.5 and b=0.5, resulting in the following directivity pattern:
 
 q   i (ϑ)=0.5+0.5 cos(ϑ+Θ i )  (1a)
 
     By the segmentor  110  exemplarily depicted in  FIG. 3 , it is possible to obtain the at least two input segmental audio signals  115  (W i , X i , Y i , Z i ) associated with the corresponding segments Seg i  of the recording space having a predetermined directivity pattern  305 , q i (ϑ), respectively. It is pointed out here that the use of the directivity pattern  305 , q i (ϑ), for each of the segments Seg i  of the recording space allows to enhance the spatial sound quality obtained with the apparatus  100 . 
       FIG. 4  shows a schematic illustration of the generator  120  of the embodiment of the apparatus  100  in accordance with  FIG. 1  based on a parametric spatial analysis. As exemplarily depicted in  FIG. 4 , the generator  120  is configured for obtaining the plurality of parametric audio streams  125  (θ i , Ψ i , W i ). Furthermore, the plurality of parametric audio streams  125  (θ i , Ψ i , W i ) may each comprise a component W i  of the at least two input segmental audio signals  115  (W i , Y i , Z i ) and a corresponding parametric spatial information θ i , Ψ i . 
     In embodiments, the generator  120  may be configured for performing a parametric spatial analysis for each of the at least two input segmental audio signals  115  (W i , X i , Y i , Z i ) to obtain the corresponding parametric spatial information θ i , Ψ i . 
     In embodiments, the parametric spatial information θ i , Ψ i  of each of the parametric audio streams  125  (θ i , Ψ i , W i ) comprises a direction-of-arrival (DOA) parameter θ i  and/or a diffuseness parameter Ψ i . 
     In embodiments, the direction-of-arrival (DOA) parameter θ i  and the diffuseness parameter Ψ i  provided by the generator  120  exemplarily depicted in  FIG. 4  may constitute DirAC parameters for a parametric spatial audio signal processing. For example, the generator  120  is configured for generating the DirAC parameters (e.g. the DOA parameter θ i  and the diffuseness parameter Ψ i ) using a time-frequency representation of the at least two input segmental audio signals  115 . 
       FIG. 5  shows a block diagram of an embodiment of an apparatus  500  for generating a plurality of loudspeaker signals  525  (L 1 , L 2 , . . . ) from a plurality of parametric audio streams  125  (θ i , Ψ i , W i ) with a renderer  510  and a combiner  520 . In the embodiment of  FIG. 5 , the plurality of parametric audio streams  125  (θ i , Ψ i , W i ) may be derived from an input spatial audio signal (e.g. the input spatial audio signal  105  exemplarily depicted in the embodiment of  FIG. 1 ) recorded in a recording space. As shown in  FIG. 5 , the apparatus  500  comprises a renderer  510  and a combiner  520 . For example, the renderer  510  is configured for providing a plurality of input segmental loudspeaker signals  515  from the plurality of parametric audio streams  125  (θ i , Ψ i , W i ), wherein the input segmental loudspeaker signals  515  are associated with corresponding segments (Seg i ) of the recording space. Furthermore, the combiner  520  may be configured for combining the input segmental loudspeaker signals  515  to obtain the plurality of loudspeaker signals  525  (L 1 , L 2 , . . . ). 
     By providing the apparatus  500  of  FIG. 5 , it is possible to generate the plurality of loudspeaker signals  525  (L 1 , L 2 , . . . ) from the plurality of parametric audio streams  125  (θ i , Ψ i , W i ), wherein the parametric audio streams  125  (θ i , Ψ i , W i ) may be transmitted from the apparatus  100  of  FIG. 1 . Furthermore, the apparatus  500  of  FIG. 5  allows to achieve a higher quality, more realistic spatial sound reproduction using parametric audio streams derived from relatively simple and compact microphone configurations. 
     In embodiments, the renderer  510  is configured for receiving the plurality of parametric audio streams  125  (θ i , Ψ i , W i ). For example, the plurality of parametric audio streams  125  (θ i , Ψ i , W i ) each comprise a segmental audio component W i  and a corresponding parametric spatial information θ i , Ψ i . Furthermore, the renderer  510  may be configured for rendering each of the segmental audio components W i  using the corresponding parametric spatial information  505  (θ i , Ψ i ) to obtain the plurality of input segmental loudspeaker signals  515 . 
       FIG. 6  shows a schematic illustration  600  of example segments Seg i  (i=1, 2, 3, 4)  610 ,  620 ,  630 ,  640  of a recording space. In the schematic illustration  600  of  FIG. 6 , the example segments  610 ,  620 ,  630 ,  640  of the recording space each represent a subset of directions within a two-dimensional (2D) plane. In addition, the segments Seg i  of the recording space may each represent a subset of directions within a three-dimensional (3D) space. For example, the segments Seg i  representing the subsets of directions within the three-dimensional (3D) space can be similar to the segments  610 ,  620 ,  630 ,  640  exemplarily depicted in  FIG. 6 . According to the schematic illustration  600  of  FIG. 6 , four example segments  610 ,  620 ,  630 ,  640  for the apparatus  100  of  FIG. 1  are exemplarily shown. However, it is also possible to use a different number of segments Seg i  (i=1, 2, . . . , n, wherein i is an integer index, and n denotes the number of segments). The example segments  610 ,  620 ,  630 ,  640  may each be represented in a polar coordinate system (see, e.g.  FIG. 6 ). For the three-dimensional (3D) space, the segments Seg i  may similarly be represented in a spherical coordinate system. 
     In embodiments, the segmentor  110  exemplarily shown in  FIG. 1  may be configured to use the segments Seg i  (e.g. the example segments  610 ,  620 ,  630 ,  640  of  FIG. 6 ) for providing the at least two input segmental audio signals  115  (W i , X i , Y i , Z i ). By using the segments (or sectors), it is possible to realize a segment-based (or sector-based) parametric model of the sound field. This enables to achieve a higher quality spatial audio recording and reproduction with a relatively compact microphone configuration. 
       FIG. 7  shows a schematic illustration  700  of an example loudspeaker signal computation for two segments or sectors of a recording space. In the schematic illustration  700  of  FIG. 7 , the embodiment of the apparatus  100  for generating the plurality of parametric audio streams  125  (θ i , Ψ i , W i ) and the embodiment of the apparatus  500  for generating the plurality of loudspeaker signals  525  (L 1 , L 2 , . . . ) are exemplarily depicted. As shown in the schematic illustration  700  of  FIG. 7 , the segmentor  110  may be configured for receiving the input spatial audio signal  105  (e.g. microphone signal). Furthermore, the segmentor  110  may be configured for providing the at least two input segmental audio signals  115  (e.g. segmental microphone signals  715 - 1  of a first segment and segmental microphone signals  715 - 2  of a second segment). The generator  120  may comprise a first parametric spatial analysis block  720 - 1  and a second parametric spatial analysis block  720 - 2 . Furthermore, the generator  120  may be configured for generating the parametric audio stream for each of the at least two input segmental audio signals  115 . At the output of the embodiment of the apparatus  100 , the plurality of parametric audio streams  125  will be obtained. For example, the first parametric spatial analysis block  720 - 1  will output a first parametric audio stream  725 - 1  of a first segment, while the second parametric spatial analysis block  720 - 2  will output a second parametric audio stream  725 - 2  of a second segment. Furthermore, the first parametric audio stream  725 - 1  provided by the first parametric spatial analysis block  720 - 1  may comprise parametric spatial information (e.g. θ 1 , Ψ 1 ) of a first segment and one or more segmental audio signals (e.g. W 1 ) of the first segment, while the second parametric audio stream  725 - 2  provided by the second parametric spatial analysis block  720 - 2  may comprise parametric spatial information (e.g. ϑ 2 , Ψ 2 ) of a second segment and one or more segmental audio signals (e.g. W 2 ) of the second segment. The embodiment of the apparatus  100  may be configured for transmitting the plurality of parametric audio streams  125 . As also shown in the schematic illustration  700  of  FIG. 7 , the embodiment of the apparatus  500  may be configured for receiving the plurality of parametric audio streams  125  from the embodiment of the apparatus  100 . The renderer  510  may comprise a first rendering unit  730 - 1  and a second rendering unit  730 - 2 . Furthermore, the renderer  510  may be configured for providing the plurality of input segmental loudspeaker signals  515  from the received plurality of parametric audio streams  125 . For example, the first rendering unit  730 - 1  may be configured for providing input segmental loudspeaker signals  735 - 1  of a first segment from the first parametric audio stream  725 - 1  of the first segment, while the second rendering unit  730 - 2  may be configured for providing input segmental loudspeaker signals  735 - 2  of a second segment from the second parametric audio stream  725 - 2  of the second segment. Furthermore, the combiner  520  may be configured for combining the input segmental loudspeaker signals  515  to obtain the plurality of loudspeaker signals  525  (e.g. L 1 , L 2 , . . . ). 
     The embodiment of  FIG. 7  essentially represents a higher quality spatial audio recording and reproduction concept using a segment-based (or sector-based) parametric model of the sound field, which allows to record also complex spatial audio scenes with a relatively compact microphone configuration. 
       FIG. 8  shows a schematic illustration  800  of an example loudspeaker signal computation for two segments or sectors of a recording space using second order B-format input signals  105 . The example loudspeaker signal computation schematically illustrated in  FIG. 8  essentially corresponds to the example loudspeaker signal computation schematically illustrated in  FIG. 7 . In the schematic illustration of  FIG. 8 , the embodiment of the apparatus  100  for generating the plurality of parametric audio streams  125  and the embodiment of the apparatus  500  for generating the plurality of loudspeaker signals  525  are exemplarily depicted. As shown in  FIG. 8 , the embodiment of the apparatus  100  may be configured for receiving the input spatial audio signal  105  (e.g. B-format microphone channels such as [W, X, Y, U, V]). Here, it is to be noted that the signals U, V in  FIG. 8  are second order B-format components. The segmentor  110  exemplarily denoted by “matrixing” may be configured for generating the at least two input segmental audio signals  115  from the omnidirectional signal and the plurality of different directional signals using a mixing or matrixing operation which depends on the segments Seg i  of the recording space. For example, the at least two input segmental audio signals  115  may comprise the segmental microphone signal  715 - 1  of a first segment (e.g. [W 1 , X 1 , Y 1 ]) and the segmental microphone signals  715 - 2  of a second segment (e.g. [W 2 , X 2 , Y 2 ]). Furthermore, the generator  120  may comprise a first directional and diffuseness analysis block  720 - 1  and a second directional and diffuseness analysis block  720 - 2 . The first and the second directional and diffuseness analysis blocks  720 - 1 ,  720 - 2  exemplarily shown in  FIG. 8  essentially correspond to the first and the second parametric spatial analysis blocks  720 - 1 ,  720 - 2  exemplarily shown in  FIG. 7 . The generator  120  may be configured for generating a parametric audio stream for each of the at least two input segmental audio signals  115  to obtain the plurality of parametric audio streams  125 . For example, the generator  120  may be configured for performing a spatial analysis on the segmental microphone signals  715 - 1  of the first segment using the first directional and diffuseness analysis block  720 - 1  and for extracting a first component (e.g. a segmental audio signal W 1 ) from the segmental microphone signals  715 - 1  of the first segment to obtain the first parametric audio stream  725 - 1  of the first segment. Furthermore, the generator  120  may be configured for performing a spatial analysis on the segmental microphone signals  715 - 2  of the second segment and for extracting a second component (e.g. a segmental audio signal W 2 ) from the segmental microphone signals  715 - 2  of the second segment using the second directional and diffuseness analysis block  720 - 2  to obtain the second parametric audio stream  725 - 2  of the second segment. For example, the first parametric audio stream  725 - 1  of the first segment may comprise parametric spatial information of the first segment comprising a first direction-of-arrival (DOA) parameter θ 1  and a first diffuseness parameter Ψ 1  as well as a first extracted component W i , while the second parametric audio stream  725 - 2  of the second segment may comprise parametric spatial information of the second segment comprising a second direction-of-arrival (DOA) parameter ϑ 2  and a second diffuseness parameter Ψ 2  as well as a second extracted component W 2 . The embodiment of the apparatus  100  may be configured for transmitting the plurality of parametric audio streams  125 . 
     As also shown in the schematic illustration  800  of  FIG. 8 , the embodiment of the apparatus  500  for generating the plurality of loudspeaker signals  525  may be configured for receiving the plurality of parametric audio streams  125  transmitted from the embodiment of the apparatus  100 . In the schematic illustration  800  of  FIG. 8 , the renderer  510  comprises the first rendering unit  730 - 1  and the second rendering unit  730 - 2 . For example, the first rendering unit  730 - 1  comprises a first multiplier  802  and a second multiplier  804 . The first multiplier  802  of the first rendering unit  730 - 1  may be configured for applying a first weighting factor  803  (e.g.) √{square root over (1−Ψ)}) to the segmental audio signal W i  of the first parametric audio stream  725 - 1  of the first segment to obtain a direct sound substream  810  by the first rendering unit  730 - 1 , while the second multiplier  804  of the first rendering unit  730 - 1  may be configured for applying a second weighting factor  805  (e.g. √{square root over (Ψ)}) to the segmental audio signal W i  of the first parametric audio stream  725 - 1  of the first segment to obtain a diffuse substream  812  by the first rendering unit  730 - 1 . Furthermore, the second rendering unit  730 - 2  may comprise a first multiplier  806  and a second multiplier  808 . For example, the first multiplier  806  of the second rendering unit  730 - 2  may be configured for applying a first weighting factor  807  (e.g. √{square root over (1−Ψ)}) to the segmental audio signal W 2  of the second parametric audio stream  725 - 2  of the second segment to obtain a direct sound stream  814  by the second rendering unit  730 - 2 , while the second multiplier  808  of the second rendering unit  730 - 2  may be configured for applying a second weighting factor  809  (e.g. √{square root over (Ψ)}) to the segmental audio signal W 2  of the second parametric audio stream  725 - 2  of the second segment to obtain a diffuse substream  816  by the second rendering unit  730 - 2 . In embodiments, the first and the second weighting factors  803 ,  805 ,  807 ,  809  of the first and the second rendering units  730 - 1 ,  730 - 2  are derived from the corresponding diffuseness parameters Ψ i . According to embodiments, the first rendering unit  730 - 1  may comprise gain factor multipliers  811 , decorrelating processing blocks  813  and combining units  832 , while the second rendering unit  730 - 2  may comprise gain factor multipliers  815 , decorrelating processing blocks  817  and combining units  834 . For example, the gain factor multipliers  811  of the first rendering unit  730 - 1  may be configured for applying gain factors obtained from a vector base amplitude panning (VBAP) operation by blocks  822  to the direct sound substream  810  output by the first multiplier  802  of the first rendering unit  730 - 1 . Furthermore, the decorrelating processing blocks  813  of the first rendering unit  730 - 1  may be configured for applying a decorrelation/gain operation to the diffuse substream  812  at the output of the second multiplier  804  of the first rendering unit  730 - 1 . In addition, the combining units  832  of the first rendering unit  730 - 1  may be configured for combining the signals obtained from the gain factor multipliers  811  and the decorrelating processing blocks  813  to obtain the segmental loudspeaker signals  735 - 1  of the first segment. For example, the gain factor multipliers  815  of the second rendering unit  730 - 2  may be configured for applying gain factors obtained from a vector base amplitude panning (VBAP) operation by blocks  824  to the direct sound substream  814  output by the first multiplier  806  of the second rendering unit  730 - 2 . Furthermore, the decorrelating processing blocks  817  of the second rendering unit  730 - 2  may be configured for applying a decorrelation/gain operation to the diffuse substream  816  at the output of the second multiplier  808  of the second rendering unit  730 - 2 . In addition, the combining units  834  of the second rendering unit  730 - 2  may be configured for combining the signals obtained from the gain factor multipliers  815  and the decorrelating processing blocks  817  to obtain the segmental loudspeaker signals  735 - 2  of the second segment. 
     In embodiments, the vector base amplitude panning (VBAP) operation by blocks  822 ,  824  of the first and the second rendering unit  730 - 1 ,  730 - 2  depends on the corresponding direction-of-arrival (DOA) parameters θ i . As exemplarily depicted in  FIG. 8 , the combiner  520  may be configured for combining the input segmental loudspeaker signals  515  to obtain the plurality of loudspeaker signals  525  (e.g. L 1 , L 2 , . . . ). As exemplarily depicted in  FIG. 8 , the combiner  520  may comprise a first summing up unit  842  and a second summing up unit  844 . For example, the first summing up unit  842  is configured to sum up a first of the segmental loudspeaker signals  735 - 1  of the first segment and a first of the segmental loudspeaker signals  735 - 2  of the second segment to obtain a first loudspeaker signal  843 . In addition, the second summing up unit  844  may be configured to sum up a second of the segmental loudspeaker signals  735 - 1  of the first segment and a second of the segmental loudspeaker signals  735 - 2  of the second segment to obtain a second loudspeaker signal  845 . The first and the second loudspeaker signals  843 ,  845  may constitute the plurality of loudspeaker signals  525 . Referring to the embodiment of  FIG. 8 , it should be noted that for each segment, potentially loudspeaker signals for all loudspeakers of the playback can be generated. 
       FIG. 9  shows a schematic illustration  900  of an example loudspeaker signal computation for two segments or sectors of a recording space including a signal modification in a parametric signal representation domain. The example loudspeaker signal computation in the schematic illustration  900  of  FIG. 9  essentially corresponds to the example loudspeaker signal computation in the schematic illustration  700  of  FIG. 7 . However, the example loudspeaker signal computation in the schematic illustration  900  of  FIG. 9  includes an additional signal modification. 
     In the schematic illustration  900  of  FIG. 9 , the apparatus  100  comprises the segmentor  110  and the generator  120  for obtaining the plurality of parametric audio streams  125  (θ i , Ψ i , W i ). Furthermore, the apparatus  500  comprises the renderer  510  and the combiner  520  for obtaining the plurality of loudspeaker signals  525 . 
     For example, the apparatus  100  may further comprise a modifier  910  for modifying the plurality of parametric audio streams  125  (θ i , Ψ i , W i ) in a parametric signal representation domain. Furthermore, the modifier  910  may be configured to modify at least one of the parametric audio streams  125  (θ i , Ψ i , W i ) using a corresponding modification control parameter  905 . In this way, a first modified parametric audio stream  916  of a first segment and a second modified parametric audio stream  918  of a second segment may be obtained. The first and the second modified parametric audio streams  916 ,  918  may constitute a plurality of modified parametric audio streams  915 . In embodiments, the apparatus  100  may be configured for transmitting the plurality of modified parametric audio streams  915 . In addition, the apparatus  500  may be configured for receiving the plurality of modified parametric audio streams  915  transmitted from the apparatus  100 . 
     By providing the example loudspeaker signal computation according to  FIG. 9 , it is possible to achieve a more flexible spatial audio recording and reproduction scheme. In particular, it is possible to obtain higher quality output signals when applying modifications in the parametric domain. By segmenting the input signals before generating the plurality of parametric audio representations (streams), a higher spatial selectivity is obtained that better allows to treat different components of the captured sound field differently. 
       FIG. 10  shows a schematic illustration  1000  of example polar patterns of input segmental audio signals  115  (e.g. W i , X i , Y i ) provided by the segmentor  110  of the embodiment of the apparatus  100  for generating the plurality of parametric audio streams  125  (θ i , Ψ i , W i ) in accordance with  FIG. 1 . In the schematic illustration  1000  of  FIG. 10 , the example input segmental audio signals  115  are visualized in a respective polar coordinate system for the two-dimensional (2D) plane. Similarly, the example input segmental audio signals  115  can be visualized in a respective spherical coordinate system for the three-dimensional (3D) space. The schematic illustration  1000  of  FIG. 10  exemplarily depicts a first directional response  1010  for a first input segmental audio signal (e.g. an omnidirectional signal W i ), a second directional response  1020  of a second input segmental audio signal (e.g. a first directional signal X i ) and a third directional response  1030  of a third input segmental audio signal (e.g. a second directional signal Y i ). Furthermore, a fourth directional response  1022  with opposite sign compared to the second directional response  1020  and a fifth directional response  1032  with opposite sign compared to the third directional response  1030  are exemplarily depicted in the schematic illustration  1000  of  FIG. 10 . Thus, different directional responses  1010 ,  1020 ,  1030 ,  1022 ,  1032  (polar patterns) can be used for the input segmental audio signals  115  by the segmentor  110 . It is pointed out here that the input segmental audio signals  115  can be dependent on time and frequency, i.e. W i =W i (m, k), X i =X i (m, k), and Y i =Y i (m, k), wherein (m, k) are indices indicating a time-frequency tile in a spatial audio signal representation. 
     In this context, it should be noted that  FIG. 10  exemplarily depicts the polar diagrams for a single set of input signals, i.e. the signals  115  for a single sector i (e.g. [W i , X i , Y i ]). Furthermore, the positive and negative parts of the polar diagram plots together represent the polar diagram of a signal, respectively (for example, the parts  1020  and  1022  together show the polar diagram of signal X i , while the parts  1030  and  1032  together show the polar diagram of signal Y i .). 
       FIG. 11  shows a schematic illustration  1100  of an example microphone configuration  1110  for performing a sound field recording. In the schematic illustration  1100  of  FIG. 11 , the microphone configuration  1110  may comprise multiple linear arrays of directional microphones  1112 ,  1114 ,  1116 . The schematic illustration  1100  of  FIG. 11  exemplarily depicts how a two-dimensional (2D) observation space can be divided into different segments or sectors  1101 ,  1102 ,  1103  (e.g. Seg i , i=1, 2. 3) of the recording space. Here, the segments  1101 ,  1102 ,  1103  of  FIG. 11  may correspond to the segments Seg i  exemplarily depicted in  FIG. 6 . Similarly, the example microphone configuration  1110  can also be used in the three-dimensional (3D) observation space, wherein the three-dimensional (3D) observation space can be divided into the segments or sectors for the given microphone configuration. In embodiments, the example microphone configuration  1110  in the schematic illustration  1100  of  FIG. 11  can be used to provide the input spatial audio signal  105  for the embodiment of the apparatus  100  in accordance with  FIG. 1 . For example, the multiple linear arrays of directional microphones  1112 ,  1114 ,  1116  of the microphone configuration  1110  may be configured to provide the different directional signals for the input spatial audio signal  105 . By the use of the example microphone configuration  1110  of  FIG. 11 , it is possible to optimize the spatial audio recording quality using the segment-based (or sector-based) parametric model of the sound field. 
     In the previous embodiments, the apparatus  100  and the apparatus  500  may be configured to be operative in the time-frequency domain. 
     In summary, embodiments of the present invention relate to the field of high quality spatial audio recording and reproduction. The use of a segment-based or sector-based parametric model of the sound field allows to also record complex spatial audio scenes with relatively compact microphone configurations. In contrast to a simple global model of the sound field assumed by the current state of the art methods, the parametric information can be determined for a number of segments in which the entire observation space is divided. Therefore, the rendering for an almost arbitrary loudspeaker configuration can be performed based on the parametric information together with the recorded audio channels. 
     According to embodiments, for a planar two-dimensional (2D) sound field recording, the entire azimuthal angle range of interest can be divided into multiple sectors or segments covering a reduced range of azimuthal angles. Analogously, in the 3D case the full solid angle range (azimuthal and elevation) can be divided into sectors or segments covering a smaller angle range. The different sectors or segments may also partially overlap. 
     According to embodiments, each sector or segment is characterized by an associated directional measure, which can be used to specify or refer to the corresponding sector or segment. The directional measure can, for example, be a vector pointing to (or from) the center of the sector or segment, or an azimuthal angle in the 2D case, or a set of an azimuth and an elevation angle in the 3D case. The segment or sector can be referred to as both a subset of directions within a 2D plane or within a 3D space. For presentational simplicity, the previous examples were exemplarily described for the 2D case; however the extension to 3D configurations is straightforward. 
     With reference to  FIG. 6 , the directional measure may be defined as a vector which, for the segment Seg 3 , points from the origin, i.e. the center with the coordinate (0, 0), to the right, i.e. towards the coordinate (1, 0) in the polar diagram, or the azimuthal angle of 0° if, in  FIG. 6 , angles are counted from (or referred to) the x-axis (horizontal axis). 
     Referring to the embodiment of  FIG. 1 , the apparatus  100  may be configured to receive a number of microphone signals as an input (input spatial audio signal  105 ). These microphone signals can, for example, either result from a real recording or can be artificially generated by a simulated recording in a virtual environment. From these microphone signals, corresponding segmental microphone signals (input segmental audio signals  115 ) can be determined, which are associated with the corresponding segments (Seg i ). The segmental microphone signals feature specific characteristics. Their directional pick-up pattern may show a significantly increased sensitivity within the associated angular sector compared to the sensitivity outside this sector. An example of the segmentation of a full azimuth range of 360° and the pick-up patterns of the associated segmental microphone signals were illustrated with reference to  FIG. 6 . In the example of  FIG. 6 , the directivity of the microphones associated with the sectors exhibit cardioid patterns which are rotated in accordance to the angular range covered by the corresponding sector. For example, the directivity of the microphone associated with the sector  3  (Seg 3 ) pointing towards 0° is also pointing towards 0°. Here, it should be noted that in the polar diagrams of  FIG. 6 , the direction of the maximum sensitivity is the direction in which the radius of the depicted curve comprises the maximum. Thus, Seg 3  has the highest sensitivity for sound components which come from the right. In other words, the segment Seg 3  has its advantageous direction at the azimuthal angle of 0° (assuming that angles are counted from the x-axis). 
     According to embodiments, for each sector, a DOA parameter (θ i ) can be determined together with a sector-based diffuseness parameter (Ψ i ). In a simple realization, the diffuseness parameter (Ψ i ) may be the same for all sectors. In principle, any advantageous DOA estimation algorithm can be applied (e.g. by the generator  120 ). For example, the DOA parameter (θ i ) can be interpreted to reflect the opposite direction in which most of the sound energy is traveling within the considered sector. Accordingly, the sector-based diffuseness relates to the ratio of the diffuse sound energy and the total sound energy within the considered sector. It is to be noted that the parameter estimation (such as performed with the generator  120 ) can be performed time-variantly and individually for each frequency band. 
     According to embodiments, for each sector, a directional audio stream (parametric audio stream) can be composed including the segmental microphone signal (W i ) and the sector-based DOA and diffuseness parameters (θ i , Ψ i ) which predominantly describe the spatial audio properties of the sound field within the angular range represented by that sector. For example, the loudspeaker signals  525  for playback can be determined using the parametric directional information (θ i , Ψ i ) and one or more of the segmental microphone signals  125  (e.g. W i ). Thereby, a set of segmental loudspeaker signals  515  can be determined for each segment which can then be combined such as by the combiner  520  (e.g. summed up or mixed) to build the final loudspeaker signals  525  for playback. The direct sound components within a sector can, for example, be rendered as point-like sources by applying an example vector base amplitude panning (as described in V. Pulkki: Virtual sound source positioning using Vector Base Amplitude Panning J. Audio Eng. Soc., Vol. 45, pp. 456-466, 1997), whereas the diffuse sound can be played back from several loudspeakers at the same time. 
     The block diagram in  FIG. 7  illustrates the computation of the loudspeaker signals  525  as described above for the case of two sectors. In  FIG. 7 , bold arrows represent audio signals, whereas thin arrows represent parametric signals or control signals. In  FIG. 7 , the generation of the segmental microphone signals  115  by the segmentor  110 , the application of the parametric spatial signal analysis (blocks  720 - 1 ,  720 - 1 ) for each sector (e.g. by the generator  120 ), the generation of the segmental loudspeaker signals  515  by the renderer  510  and the combining of the segmental loudspeaker signals  515  by the combiner  520  are schematically illustrated. 
     In embodiments, the segmentor  110  may be configured for performing the generation of the segmental microphone signals  115  from a set of microphone input signals  105 . Furthermore, the generator  120  may be configured for performing the application of the parametric spatial signal analysis for each sector such that the parametric audio streams  725 - 1 ,  725 - 2  for each sector will be obtained. For example, each of the parametric audio streams  725 - 1 ,  725 - 2  may consist of at least one segmental audio signal (e.g. W 1 , W 2 , respectively) as well as associated parametric information (e.g. DOA parameters θ 1 , θ 2  and diffuseness parameters Ψ 1 , Ψ 2 , respectively). The renderer  510  may be configured for performing the generation of the segmental loudspeaker signals  515  for each sector based on the parametric audio streams  725 - 1 ,  725 - 2  generated for the particular sectors. The combiner  520  may be configured for performing the combining of the segmental loudspeaker signals  515  to obtain the final loudspeaker signals  525 . 
     The block diagram in  FIG. 8  illustrates the computation of the loudspeaker signals  525  for the example case of two sectors shown as an example for a second order B-format microphone signal application. As shown in the embodiment of  FIG. 8 , two (sets of) segmental microphone signals  715 - 1  (e.g. [W 1 , X 1 , Y 1 ]) and  715 - 2  (e.g. [W 2 , X 2 , Y 2 ]) can be generated from a set of input microphone signals  105  by a mixing or matrixing operation (e.g. by block  110 ) as described before. For each of the two segmental microphone signals, a directional audio analysis (e.g. by blocks  720 - 1 ,  720 - 2 ) can be performed, yielding the directional audio streams  725 - 1  (e.g. θ 1 , Ψ 1 , W 1 ) and  725 - 2  (e.g. ϑ 2 , Ψ 2 , W 2 ) for the first sector and the second sector, respectively. 
     In  FIG. 8 , the segmental loudspeaker signals  515  can be generated separately for each sector as follows. The segmental audio component W i  can be divided into two complementary substreams  810 ,  812 ,  814 ,  816  by weighting with multipliers  803 ,  805 ,  807 ,  809  derived from the diffuseness parameter Ψ i . One substream may carry predominately direct sound components, whereas the other substream may carry predominately diffuse sound components. The direct sound substreams  810 ,  814  can be rendered using panning gains  811 ,  815  determined by the DOA parameter θ i , whereas the diffuse substreams  812 ,  816  can be rendered incoherently using decorrelating processing blocks  813 ,  817 . 
     As an example last step, the segmental loudspeaker signals  515  can be combined (e.g. by block  520 ) to obtain the final output signals  525  for loudspeaker reproduction. 
     Referring to the embodiment of  FIG. 9 , it should be mentioned that the estimated parameters (within the parametric audio streams  125 ) may also be modified (e.g. by modifier  910 ) before the actual loudspeaker signals  525  for playback are determined. For example, the DOA parameter θ i  may be remapped to achieve a manipulation of the sound scene. In other cases, the audio signals (e.g. W i ) of certain sectors may be attenuated before computing the loudspeaker signals  525  if the sound coming from a certain or all directions included in these sectors are not desired. Analogously, diffuse sound components can be attenuated if mainly or only direct sound should be rendered. This processing including a modification  910  of the parametric audio streams  125  is exemplarily illustrated in  FIG. 9  for the example of a segmentation into two segments. 
     An embodiment of a sector-based parameter estimation in the example 2D case performed with the previous embodiments will be described in the following. It is assumed that the microphone signals used for capturing can be converted into so-called second-order B-format signals. Second-order B-format signals can be described by the shape of the directivity patterns of the corresponding microphones:
 
 b   W (ϑ)=1  (2)
 
 b   X (ϑ)=cos(ϑ)  (3)
 
 b   Y (ϑ)=sin(ϑ)  (4)
 
 b   U (ϑ)=cos(2ϑ)  (5)
 
 b   Y (ϑ)=sin(2ϑ)  (6)
 
where ϑ denotes the azimuth angle. The corresponding B-format signals (e.g. input  105  of  FIG. 8 ) are denoted by W(m, k), X(m, k), Y(m, k), U(m, k) and V(m, k), where m and k represent a time and frequency index, respectively. It is now assumed that the segmental microphone signal associated with the i&#39;th sector has a directivity pattern q i (ϑ). We can then determine (e.g. by block  110 ) the additional microphone signals  115 , W i (m, k), X i (m, k), Y i (m, k) having a directivity pattern which can be expressed by
 
 b   W     i   (ϑ)= q   i (ϑ)  (7)
 
 b   X     i   (ϑ)= q   i (ϑ)cos(ϑ)  (8)
 
 b   Y     i   (ϑ)= q   i (ϑ)sin(ϑ)  (9)
 
     Some examples for the directivity patterns of the described microphone signals in case of an example cardioid pattern q i (ϑ)=0.5+0.5 cos(ϑ+Θ i ) are shown in  FIG. 10 . The advantageous direction of the i&#39;th sector depends on an azimuth angle Θ i . In  FIG. 10 , the dashed lines indicate the directional responses  1022 ,  1032  (polar patterns) with opposite sign compared to the directional responses  1020 ,  1030  depicted with solid lines. 
     Note that for the example case of Θ i =0, the signals W i (m, k), X i (m, k), Y i (m, k) can be determined from the second-order B-format signals by mixing the input components W, X, Y, U, V according to
 
 W   i ( m,k )=0.5 W ( m,k )+0.5 X ( m,k )  (10)
 
 X   i ( m,k )=0.25 W ( m,k )+0.5 X ( m,k )+0.25 U ( m,k )  (11)
 
 Y   i ( m,k )=0.5 Y ( m,k )+0.25 V ( m,k )  (12)
 
     This mixing operation is performed e.g. in  FIG. 2  in building block  110 . Note that a different choice of q i (ϑ) leads to a different mixing rule to obtain the components W i , X i , Y i  from the second-order B-format signals. 
     From the segmental microphone signals  115 , W i (m, k), X i (m, k), Y i (m, k), we can then determine (e.g. by block  120 ) the DOA parameter θ i  associated with the i&#39;th sector by computing the sector-based active intensity vector 
                       I     a   i       ⁡     (     m   ,   k     )       =       -     1     2   ⁢           ⁢     ρ   0     ⁢   c         ⁢   Re   ⁢     {         W   i   *     ⁡     (     m   ,   k     )       ·     [             X   i     ⁡     (     m   ,   k     )                   Y   i     ⁡     (     m   ,   k     )             ]       }               (   13   )               
where Re {A} denotes the real part of the complex number A and * denotes complex conjugate. Furthermore, ρ 0  is the air density and c is the sound velocity. The desired DOA estimate θ i (m, k), for example represented by the unit vector e i (m, k), can be obtained by
 
                       e   i     ⁡     (     m   ,   k     )       =     -         I     a   i       ⁡     (     m   ,   k     )                I     a   i       ⁡     (     m   ,   k     )                        (   14   )               
We can further determine the sector-based, sound field energy related quantity
 
                       E   i     ⁡     (     m   ,   k     )       =       1     4   ⁢           ⁢     ρ   0     ⁢     c   2         ⁢     (                W   i     ⁡     (     m   ,   k     )            2     +              X   i     ⁡     (     m   ,   k     )            2     +              Y   i     ⁡     (     m   ,   k     )            2       )               (   15   )               
The desired diffuseness parameter Ψ i (m, k) of the i&#39;th sector can then be determined by
 
                       Ψ   i     ⁡     (     m   ,   k     )       =     g   ⁡     (     1   -            E   ⁢     {       I     a   i       ⁡     (     m   ,   k     )       }                cE   i     ⁡     (     m   ,   k     )           )               (   16   )               
where g denotes a suitable scaling factor, E{ } is the expectation operator and ∥ ∥ denotes the vector norm. It can be shown that the diffuseness parameter Ψ i (m, k) is zero if only a plane wave is present and takes a positive value smaller than or equal to one in the case of purely diffuse sound fields. In general, an alternative mapping function can be defined for the diffuseness which exhibits a similar behavior, i.e. giving 0 for direct sound only, and approaching 1 for a completely diffuse sound field.
 
     Referring to the embodiment of  FIG. 11 , an alternative realization for the parameter estimation can be used for different microphone configurations. As exemplarily illustrated in  FIG. 11 , multiple linear arrays  1112 ,  1114 ,  1116  of directional microphones can be used.  FIG. 11  also shows an example of how the 2D observation space can be divided into sectors  1101 ,  1102 ,  1103  for the given microphone configuration. The segmental microphone signals  115  can be determined by beam forming techniques such as filter and sum beam forming applied to each of the linear microphone arrays  1112 ,  1114 ,  1116 . The beamforming may also be omitted, i.e. the directional patterns of the directional microphones may be used as the only means to obtain segmental microphone signals  115  that show the desired spatial selectivity for each sector (Seg i ). The DOA parameter θ i  within each sector can be estimated using common estimation techniques such as the “ESPRIT” algorithm (as described in R. Roy and T. Kailath: ESPRIT-estimation of signal parameters via rotational invariance techniques, IEEE Transactions on Acoustics, Speech and Signal Processing, vol. 37, no. 7, pp. 984995, July 1989). The diffuseness parameter Ψ i  for each sector can, for example, be determined by evaluating the temporal variation of the DOA estimates (as described in J. Ahonen, V. Pulkki: Diffuseness estimation using temporal variation of intensity vectors, IEEE Workshop on Applications of Signal Processing to Audio and Acoustics, 2009. WAS-PAA &#39;09., pp. 285-288, 18-21 Oct. 2009). Alternatively, known relations of the coherence between different microphones and the direct-to-diffuse sound ratio (as described in O. Thiergart, G. Del Galdo, E.A.P. Habets: Signal-to-reverberant ratio estimation based on the complex spatial coherence between omnidirectional microphones, IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), 2012, pp. 309-312, 25-30 Mar. 2012) can be employed. 
       FIG. 12  shows a schematic illustration  1200  of an example circular array of omnidirectional microphones  1210  for obtaining higher order microphone signals (e.g. the input spatial audio signal  105 ). In the schematic illustration  1200  of  FIG. 12 , the circular array of omnidirectional microphones  1210  comprises, for example, 5 equidistant microphones arranged along a circle (dotted line) in a polar diagram. In embodiments, the circular array of omnidirectional microphones  1210  can be used to obtain the higher order (HO) microphone signals, as will be described in the following. In order to compute the example second-order microphone signals U and V from the omnidirectional microphone signals (provided by the omnidirectional microphones  1210 ), at least 5 independent microphone signals should be used. This can be achieved elegantly, e.g. using a Uniform Circular Array (UCA) as the one exemplarily shown in  FIG. 12 . The vector obtained from the microphone signals at a certain time and frequency can, for example, be transformed with a DFT (Discrete Fourier transform). The microphone signals W, X, Y, U and V (i.e. the input spatial audio signal  105 ) can then be obtained by a linear combination of the DFT coefficients. Note that the DFT coefficients represent the coefficients of the Fourier series calculated from the vector of the microphone signals. 
     Let γ m  denote the generalized m-th order microphone signal, defined by the directivity patterns
 
γ m   (cos)   pattern: cos( m ϑ)
 
γ m   (sin)   pattern: sin( m ϑ)  (17)
 
where ϑ denotes an azimuth angle so that
 
 X=γ   1   (cos)  
 
 Y=γ   1   (sin)  
 
 U=γ   2   (cos)  
 
 V=γ   2   (sin)   (18)
 
Then, it can be proven that
 
                       Υ   m     (   cos   )       =       A   m       2   ⁢     j   m           ⁢     
     ⁢       Υ   m     (   sin   )       =       B   m       2   ⁢     j   m           ⁢     
     ⁢   where   ⁢     
     ⁢       A   m     =       1       J   m     ⁡     (   kr   )         ⁢     (         P   °     m     +       P   °       -   m         )         ⁢     
     ⁢       B   m     =       j   ·     1       J   m     ⁡     (   kr   )           ⁢     (         P   °     m     -       P   °       -   m         )         ⁢     
     ⁢       P   ⁡     (     φ   ,   r     )       =       ∑     m   =     -   ∞       ∞     ⁢         P   °     m     ⁢     e     jm   ⁢           ⁢   φ                     (   19   )               
where j is the imaginary unit, k is the wave number, r and φ are the radius and the azimuth angle defining a polar coordinate system, J m (·) is the m-order Bessel function of the first kind, and    m  are the coefficients of the Fourier series of the pressure signal measured on the polar coordinates (r, φ).
 
     Note that care has to be taken in the array design and implementation of the calculation of the (higher order) B-format signals to avoid excessive noise amplification due to the numerical properties of the Bessel function. 
     Mathematical background and derivations related to the described signal transformation can be found, e.g. in A. Kuntz,  Wave field analysis using virtual circular microphone arrays , Dr. Hut, 2009, ISBN: 978-3-86853-006-3. 
     Further embodiments of the present invention relate to a method for generating a plurality of parametric audio streams  125  (θ i , Ψ i , W i ) from an input spatial audio signal  105  obtained from a recording in a recording space. For example, the input spatial audio signal  105  comprises an omnidirectional signal W and a plurality of different directional signals X, Y, Z, U, V. The method comprises providing at least two input segmental audio signals  115  (W i , X i , Y i , Z i ) from the input spatial audio signal  105  (e.g. the omnidirectional signal W and the plurality of different directional signals X, Y, Z, U, V), wherein the at least two input segmental audio signals  115  (W i , X i , Y i , Z i ) are associated with corresponding segments Seg i  of the recording space. Furthermore, the method comprises generating a parametric audio stream for each of the at least two input segmental audio signals  115  (W i , X i , Y i , Z i ) to obtain the plurality of parametric audio streams  125  (θ i , Ψ i , W i ). 
     Further embodiments of the present invention relate to a method for generating a plurality of loudspeaker signals  525  (L 1 , L 2 , . . . ) from a plurality of parametric audio streams  125  (θ i , Ψ i , W i ) derived from an input spatial audio signal  105  recorded in a recording space. The method comprises providing a plurality of input segmental loudspeaker signals  515  from the plurality of parametric audio streams  125  (θ i , Ψ i , W i ), wherein the input segmental loudspeaker signals  515  are associated with corresponding segments Seg i  of the recording space. Furthermore, the method comprises combining the input segmental loudspeaker signals  515  to obtain the plurality of loudspeaker signals  525  (L 1 , L 2 , . . . ). 
     Although the present invention has been described in the context of block diagrams where the blocks represent actual or logical hardware components, the present invention can also be implemented by a computer-implemented method. In the latter case, the blocks represent corresponding method steps where these steps stand for the functionalities performed by corresponding logical or physical hardware blocks. 
     The described embodiments are merely illustrative for the principles of the present invention. It is understood that modifications and variations of the arrangements and the details described herein will be apparent to others skilled in the art. It is the intent, therefore, to be limited only by the scope of the appending patent claims and not by the specific details presented by way of description and explanation of the embodiments herein. 
     Although some aspects have been described in the context of an apparatus, it is clear that these aspects also represent a description of the corresponding method, where a block or device corresponds to a method step or a feature of a method step. Analogously, aspects described in the context of a method step also represent a description of a corresponding block or item or feature of a corresponding apparatus. Some or all of the method steps may be executed by (or using) a hardware apparatus like, for example, a microprocessor, a programmable computer or an electronic circuit. In some embodiments, some one or more of the most important method steps may be executed by such an apparatus. 
     The parametric audio streams  125  (θ i , Ψ i , W i ) can be stored on a digital storage medium or can be transmitted on a transmission medium such as a wireless transmission medium or a wired transmission medium such as the internet. 
     Depending on certain implementation requirements, embodiments of the invention can be implemented in hardware or in software. The implementation can be performed using a digital storage medium, for example a floppy disk, a DVD, a Blu-Ray, a CD, a ROM, an EPROM, an EEPROM or a FLASH memory, having electronically readable control signal stored thereon, which cooperate (or are capable of cooperating) with a programmable computer system such that the respective method is performed. Therefore, the digital storage medium may be computer readable. 
     Some embodiments according to the invention comprise a data carrier having electronically readable control signals, which are capable of cooperating with a programmable computer system, such that one of the methods described herein is performed. 
     Generally, embodiments of the present invention can be implemented as a computer program product with a program code, the program code being operative for performing 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. 
     Other embodiments comprise the computer program for performing one of the methods described herein, stored on a machine readable carrier. 
     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. 
     A further embodiment of the inventive method is therefore a data carrier (or a digital storage medium, or a computer-readable medium) comprising, recorded thereon, the computer program for performing one of the methods described herein. The data carrier, the digital storage medium or the recorded medium are typically tangible and/or non-transitionary. 
     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 may, for example, be configured to be transferred via a data communication connection, for example via the internet. 
     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. 
     A further embodiment comprises a computer having installed thereon the computer program for performing one of the methods described herein. 
     A further embodiment according to the invention comprises an apparatus or a system configured to transfer (for example, electronically or optically) a computer program for performing one of the methods described herein to a receiver. The receiver may, for example, be a computer, a mobile device, a memory device or the like. The apparatus or system may, for example, comprise a file server for transferring the computer program to the receiver. 
     In some embodiments, a programmable logic device (for example a field programmable gate array) may be used to perform some or all of the functionalities of the methods described herein. In some embodiments, a field programmable gate array may operate with a microprocessor in order to perform one of the methods described herein. Generally, the methods are advantageously performed by any hardware apparatus. 
     Embodiments of the present invention provide a high quality, realistic spatial sound recording and reproduction using simple and compact microphone configurations. 
     Embodiments of the present invention are based on directional audio coding (DirAC) (as described in T. Lokki, J. Merimaa, V. Pulkki: Method for Reproducing Natural or Modified Spatial Impression in Multichannel Listening, U.S. Pat. No. 7,787,638 B2, Aug. 31, 2010 and V. Pulkki: Spatial Sound Reproduction with Directional Audio Coding. J. Audio Eng. Soc., Vol. 55, No. 6, pp. 503-516, 2007), which can be used with different microphone systems, and with arbitrary loudspeaker setups. The benefit of the DirAC is to reproduce the spatial impression of an existing acoustical environment as precisely as possible using a multichannel loudspeaker system. Within the chosen environment, responses (continuous sound or impulse responses) can be measured with an omnidirectional microphone (W i ) and with a set of microphones that enables measuring the direction-of-arrival (DOA) of sound and the diffuseness of sound. A possible method is to apply three figure-of-eight microphones (X, Y, Z) aligned with the corresponding Cartesian coordinate axis. A way to do this is to use a “SoundField” microphone, which directly yields all the desired responses. It is interesting to note that the signal of the omnidirectional microphone represents the sound pressure, whereas the dipole signals are proportionate to the corresponding elements of the particle velocity vector. 
     Form these signals, the DirAC parameters, i.e. DOA of sound and the diffuseness of the observed sound field can be measured in a suitable time/frequency raster with a resolution corresponding to that of the human auditory system. The actual loudspeaker signals can then be determined from the omnidirectional microphone signal based on the DirAC parameters (as described in V. Pulkki: Spatial Sound Reproduction with Directional Audio Coding. J. Audio Eng. Soc., Vol. 55, No. 6, pp. 503-516, 2007). Direct sound components can be played back by only a small number of loudspeakers (e.g. one or two) using panning techniques, whereas diffuse sound components can be played back from all loudspeakers at the same time. 
     Embodiments of the present invention based on DirAC represent a simple approach to spatial sound recording with compact microphone configurations. In particular, the present invention prevents some systematic drawbacks which limit the achievable sound quality and experience in practice in conventional technology. 
     In contrast to conventional DirAC, embodiments of the present invention provide a higher quality parametric spatial audio processing. Conventional DirAC relies on a simple global model for the sound field, employing only one DOA and one diffuseness parameter for the entire observation space. It is based on the assumption that the sound field can be represented by only one single direct sound component, such as a plane wave, and one global diffuseness parameter for each time/frequency tile. It turns out in practice, however, that often this simplified assumption about the sound field does not hold. This is especially true in complex, real world acoustics, e.g. where multiple sound sources such as talkers or instruments are active at the same time. On the other hand, embodiments of the present invention do not result in a model mismatch of the observed sound field, and the corresponding parameter estimates are more correct. It can also be prevented that a model mismatch results, especially in cases where direct sound components are rendered diffusely and no direction can be perceived when listening to the loudspeaker outputs. In embodiments, decorrelators can be used for generating uncorrelated diffuse sound played back from all loudspeakers (as described in V. Pulkki: Spatial Sound Reproduction with Directional Audio Coding. J. Audio Eng. Soc., Vol. 55, No. 6, pp. 503-516, 2007). In contrast to conventional technology, where decorrelators often introduce an undesired added room effect, it is possible with the present invention to more correctly reproduce sound sources which have a certain spatial extent (as opposed to the case of using the simple sound field model of DirAC which is not capable of precisely capturing such sound sources). 
     Embodiments of the present invention provide a higher number of degrees of freedom in the assumed signal model, allowing for a better model match in complex sound scenes. 
     Furthermore, in case of using directional microphones to generate sectors (or any other time-invariant linear, e.g. physical, means), an increased inherent directivity of microphones can be obtained. Therefore, there is less need for applying time-variant gains to avoid vague directions, crosstalk, and coloration. This leads to less nonlinear processing in the audio signal path, resulting in higher quality. 
     In general, more direct sound components can be rendered as direct sound sources (point sources/plane wave sources). As a consequence, less decorrelation artifacts occur, more (correctly) localizable events are perceivable, and a more exact spatial reproduction is achievable. 
     Embodiments of the present invention provide an increased performance of a manipulation in the parametric domain, e. g. directional filtering (as described in M. Kallinger, H. Ochsenfeld, G. Del Galdo, F. Kuech, D. Mahne, R. Schultz-Amling, and O. Thiergart: A Spatial Filtering Approach for Directional Audio Coding, 126th AES Convention, Paper 7653, Munich, Germany, 2009), compared to the simple global model, since a larger fraction of the total signal energy is attributed to direct sound events with a correct DOA associated to it, and a larger amount of information is available. The provision of more (parametric) information allows, for example, to separate multiple direct sound components or also direct sound components from early reflections impinging from different directions. 
     Specifically, embodiments provide the following features. In the 2D case, the full azimuthal angle range can be split into sectors covering reduced azimuthal angle ranges. In the 3D case, the full solid angle range can be split into sectors covering reduced solid angle ranges. Each sector can be associated with an advantageous angle range. For each sector, segmental microphone signals can be determined from the received microphone signals, which predominantly consist of sound arriving from directions that are assigned to/covered by the particular sector. These microphone signals may also be determined artificially by simulated virtual recordings. For each sector, a parametric sound field analysis can be performed to determine directional parameters such as DOA and diffuseness. For each sector, the parametric directional information (DOA and diffuseness) predominantly describes the spatial properties of the angular range of the sound field that is associated to the particular sector. In case of playback, for each sector, loudspeaker signals can be determined based on the directional parameters and the segmental microphone signals. The overall output is then obtained by combining the outputs of all sectors. In case of manipulation, before computing the loudspeaker signals for playback, the estimated parameters and/or segmental audio signals may also be modified to achieve a manipulation of the sound scene. 
     While this invention has been described in terms of several embodiments, there are alterations, permutations, and equivalents which fall within the scope of this invention. It should also be noted that there are many alternative ways of implementing the methods and compositions of the present invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations and equivalents as fall within the true spirit and scope of the present invention.