Methods, apparatus and systems for encoding and decoding of directional sound sources

1. A method for encoding directional audio data, comprising:

receiving a mono audio signal corresponding to an audio object and a representation of a radiation pattern corresponding to the audio object, the radiation pattern comprising sound levels corresponding to plurality of sample times, a plurality of frequency bands and a plurality of directions;

encoding the mono audio signal;

resealing the radiation pattern to an amplitude of the radiation pattern in a particular direction on a per frequency basis to determine a normalized radiation pattern; and

encoding the normalized radiation pattern to determine radiation pattern metadata,

wherein the encoding of the normalized radiation pattern comprises determining a spherical harmonic transform of the representation of the normalized radiation pattern and compressing the spherical harmonic transform to obtain encoded radiation pattern metadata corresponding to the normalized radiation pattern.

2. The method of claim 1 , further comprising encoding a plurality of directional audio objects based on a cluster of audio objects, wherein the radiation pattern is representative of a centroid that reflects an average sound level value for each frequency band.

3. The method of claim 2 , wherein the plurality of directional audio objects is encoded as a single directional audio object whose directivity corresponds with a time-varying energy-weighted average of each audio object's spherical harmonic coefficients, and/or wherein the encoded radiation pattern metadata indicates a position of a cluster of audio objects that is an average of corresponding positions of the plurality of directional audio objects.

4. The method of claim 1 , further comprising encoding group metadata regarding a radiation pattern of a group of directional audio objects.

5. The method of claim 1 , wherein compressing the spherical harmonic transform comprises at least one of a Singular Value Decomposition method, principal component analysis, discrete cosine transforms, data-independent bases, or eliminating spherical harmonic coefficients of the spherical harmonic transform that are above a threshold order of spherical harmonic coefficients.

6. A method for decoding audio data, comprising:

receiving an encoded core audio signal, encoded radiation pattern metadata and encoded audio object metadata, wherein the audio object metadata includes at least one of time-varying 3 degrees of freedom (DoF) or 6DoF source orientation information;

decoding the encoded core audio signal to determine a core audio signal;

decoding the encoded radiation pattern metadata to determine a decoded radiation pattern;

decoding the audio object metadata; and

rendering the core audio signal based on the audio object metadata and the decoded radiation pattern.

7. The method of claim 6 , wherein the core audio signal comprises a plurality of directional objects based on a cluster of objects, and wherein the decoded radiation pattern is representative of a centroid that reflects an average value for each frequency band.

8. The method of claim 6 , wherein the encoded radiation pattern metadata corresponds with a time- and frequency-varying set of spherical harmonic coefficients.

9. The method of claim 6 , wherein the encoded radiation pattern metadata comprises audio object type metadata.

10. The method of claim 9 , wherein the audio object type metadata indicates parametric directivity pattern data and wherein the parametric directivity pattern data includes one or more functions selected from a list of functions that consists of a cosine function, a sine function or a cardioidal function.

11. The method of claim 9 , wherein the audio object type metadata indicates dynamic directivity pattern data and wherein the dynamic directivity pattern data corresponds with a time- and frequency-varying set of spherical harmonic coefficients.

12. The method of claim 11 , further comprising receiving the dynamic directivity pattern data prior to receiving the encoded core audio signal.

13. The method of claim 6 , wherein the rendering is based on applying subband gains, based at least in part on the decoded radiation pattern, to the decoded core audio signal.

14. The method of claim 9 wherein the audio object type metadata indicates database directivity pattern data and wherein decoding the encoded radiation pattern metadata to determine the decoded radiation pattern comprises querying a directivity data structure that includes audio object types and corresponding directivity pattern data.

15. An audio decoding apparatus, comprising:

an interface system; and

a control system configured for:

receiving, via the interface system, audio data corresponding to at least one audio object, the audio data including a monophonic audio signal, audio object position metadata, audio object size metadata, and a rendering parameter, wherein the audio object position metadata includes at least one of time-varying 3 degrees of freedom (DoF) or 6DoF source orientation information;

determining whether the rendering parameter indicates a positional mode or a directivity mode; and, upon determining that the rendering parameter indicates a directivity mode, rendering the audio data for reproduction via at least one loudspeaker according to a directivity pattern indicated by at least one of the audio object position metadata or the audio object size metadata.

16. The apparatus of claim 15 , wherein rendering the audio data comprises interpreting the audio object position metadata as audio object orientation metadata.

17. The apparatus of claim 16 , wherein the audio object position metadata comprises at least one of x,y,z coordinate data, spherical coordinate data or cylindrical coordinate data and wherein the audio object orientation metadata comprises yaw, pitch and roll data.

18. The apparatus of claim 15 , wherein rendering the audio data comprises interpreting the audio object size metadata as directivity metadata that corresponds to the directivity pattern.

19. The apparatus of claim 15 , wherein rendering the audio data comprises querying a data structure that includes a plurality of directivity patterns and mapping at least one of the audio object position metadata or the audio object size metadata to one or more of the directivity patterns.

20. The apparatus of claim 19 , wherein the control system is configured for receiving, via the interface system, the data structure.

21. The apparatus of claim 20 , wherein the data structure is received prior to the audio data.

22. The apparatus of claim 15 , wherein the audio data is received in a Dolby Atmos format, and/or wherein the audio object position metadata corresponds to world coordinates or model coordinates.