Representing spatial audio by means of an audio signal and associated metadata

1. A method for representing spatial audio, the spatial audio being a combination of directional sound and diffuse sound, the method comprising:

creating a single- or multi-channel downmix audio signal x by downmixing input audio signals from a plurality of microphones (m 1 , m 2 , m 3 ) in an audio capture unit capturing the spatial audio, wherein the downmixing is described by:

x=D·m

wherein:

D is a downmix matrix containing downmix coefficients defining weights for each input audio signal from the plurality of microphones, and

m is a matrix representing the input audio signals from the plurality of microphones;

determining first metadata parameters associated with the downmix audio signal, wherein the first metadata parameters are indicative of one or more of: a relative time delay value, a gain value, and a phase value associated with each input audio signal; and

combining the created downmix audio signal and the first metadata parameters into a representation of the spatial audio.

2. The method of claim 1 , wherein combining the created downmix audio signal and the first metadata parameters into a representation of the spatial audio further comprises:

including second metadata parameters in the representation of the spatial audio, the second metadata parameters being indicative of a downmix configuration for the input audio signals.

3. The method of claim 1 , wherein the first metadata parameters are determined for one or more frequency bands of the microphone input audio signals.

4. The method of claim 1 , wherein the downmix coefficients are chosen to select the input audio signal of the microphone currently having the best signal to noise ratio with respect to the directional sound, and to discard signal input audio signals from any other microphones.

5. The method of claim 4 , wherein the selection is made for per Time-Frequency (TF) tile basis.

6. The method of claim 5 , wherein the selection is made for all frequency bands of a particular audio frame.

7. The method of claim 6 , wherein the maximizing is done for a particular audio frame.

8. The method of claim 1 , wherein the downmix coefficients are chosen to maximize the signal to noise ratio with respect to the directional sound, when combining the input audio signals from the different microphones.

9. The method of claim 8 , wherein the maximizing is done for a particular frequency band.

10. The method of claim 1 , wherein determining first metadata parameters includes analyzing one or more of: delay, gain and phase characteristics of the input audio signals from the plurality microphones.

11. The method of claim 1 , wherein the first metadata parameters are determined on a per Time-Frequency (TF) tile basis.

12. The method of claim 1 , wherein at least a portion of the downmixing occurs in the audio capture unit.

13. The method of claim 1 , wherein at least a portion of the downmixing occurs in an encoder.

14. The method of claim 1 , further comprising:

in response to detecting more than one source of directional sound, determining first metadata for each source.

15. The method of claim 1 , wherein the representation of the spatial audio includes at least one of the following parameters: a direction index, a direct-to-total energy ratio; a spread coherence; an arrival time, gain and phase for each microphone; a diffuse-to-total energy ratio; a surround coherence; a remainder-to-total energy ratio; and a distance.

16. The method of claim 1 , wherein a metadata parameter of the second or first metadata parameters indicates whether the created downmix audio signal is generated from: left right stereo signals, planar First Order Ambisonics (FOA) signals, or First Order Ambisonics component signals.

17. The method of claim 1 , wherein the representation of the spatial audio contains metadata parameters organized into a definition field and a selector field, the definition field specifying at least one delay compensation parameter set associated with the plurality of microphones, and the selector field specifying the selection of a delay compensation parameter set.

18. The method of claim 17 , wherein the selector field specifies what delay compensation parameter set applies to any given Time-Frequency tile.

19. The method of claim 17 , wherein the metadata parameters in the representation of the spatial audio further include a field specifying the applied gain adjustment and a field specifying the phase adjustment.

20. The method of claim 19 , wherein the gain adjustment is approximately in the interval of [+10 dB, −30 dB].

21. The method of claim 1 , wherein the relative time delay value is approximately in the interval of [−2.0 ms, 2.0 ms].

22. The method of claim 1 , wherein at least parts of the first and/or second metadata elements are determined at the audio capturing device using lookup-tables stored in a memory.

23. The method of claim 1 , wherein at least parts of the first and/or second metadata elements are determined at a remote device connected to the audio capturing device.

24. A computer program product comprising a non-transitory computer-readable medium with instructions for performing the method of claim 1 .

25. A system for representing spatial audio, comprising:

a receiving component configured to receive input audio signals from a plurality of microphones (m 1 , m 2 , m 3 ) in an audio capture unit capturing the spatial audio;

a downmixing component configured to create a single- or multi-channel downmix audio signal x by downmixing the received audio signals, wherein the downmixing is described by:

x=D·m

wherein:

D is a downmix matrix containing downmix coefficients defining weights for each input audio signal from the plurality of microphones, and

m is a matrix representing the input audio signals from the plurality of microphones;

a metadata determination component configured to determine first metadata parameters associated with the downmix audio signal, wherein the first metadata parameters are indicative of one or more of: a relative time delay value, a gain value, and a phase value associated with each input audio signal; and

a combination component configured to combine the created downmix audio signal and the first metadata parameters into a representation of the spatial audio.

26. The system of claim 25 , wherein the combination component is further configured to include second metadata parameters in the representation of the spatial audio, the second metadata parameters being indicative of a downmix configuration for the input audio signals.

27. A method of storing data in a data format for representing spatial audio, comprising:

receiving audio data; and

transforming the audio data into a computer-readable format, including:

writing, on a non-transitory computer-readable medium, a single- or multi-channel downmix audio signal x resulting from a downmix of input audio signals from a plurality of microphones (m 1 , m 2 , m 3 ) in an audio capture unit capturing the spatial audio, wherein the downmix is described by:

x=D·m

wherein:

D is a downmix matrix containing downmix coefficients defining weights for each input audio signal from the plurality of microphones, and

m is a matrix representing the input audio signals from the plurality of microphones; and

writing, on the non-transitory computer-readable medium, first metadata parameters indicative of one or more of: a downmix configuration for the input audio signals, a relative time delay value, a gain value, and a phase value associated with each input audio signal.

28. The method of claim 27 , wherein transforming the audio data further comprises writing second metadata parameters indicative of a downmix configuration for the input audio signals.

29. An encoder configured to:

receive a representation of spatial audio, the representation comprising:

a single- or multi-channel downmix audio signal x created by downmixing input audio signals from a plurality of microphones (m 1 , m 2 , m 3 ) in an audio capture unit capturing the spatial audio, wherein the downmixing is described by:

x=D·m

wherein:

D is a downmix matrix containing downmix coefficients defining weights for each input audio signal from the plurality of microphones, and

m is a matrix representing the input audio signals from the plurality of microphones, and

first metadata parameters associated with the downmix audio signal, wherein the first metadata parameters are indicative of one or more of: a relative time delay value, a gain value, and a phase value associated with each input audio signal; and

perform one of:

encoding the single- or multi-channel downmix audio signal into a bitstream using the first metadata, and

encoding the single or multi-channel downmix audio signal and the first metadata into a bitstream.

30. The encoder of claim 29 , wherein:

the representation of spatial audio further includes second metadata parameters being indicative of a downmix configuration for the input audio signals; and

the encoder is configured to encode the single- or multi-channel downmix audio signal into a bitstream using the first and second metadata parameters.

31. The encoder of claim 30 , wherein a portion of the downmixing occurs in the audio capture unit and a portion of the downmixing occurs in the encoder.

32. A decoder configured to:

receive a bitstream indicative of a coded representation of spatial audio, the representation comprising:

a single- or multi-channel downmix audio signal x created by downmixing input audio signals from a plurality of microphones (m 1 , m 2 , m 3 ) in an audio capture unit ( 202 ) capturing the spatial audio, wherein the downmixing is described by:

x=D·m

wherein:

D is a downmix matrix containing downmix coefficients defining weights for each input audio signal from the plurality of microphones, and

m is a matrix representing the input audio signals from the plurality of microphones, and

first metadata parameters associated with the downmix audio signal, wherein the first metadata parameters are indicative of one or more of: a relative time delay value, a gain value, and a phase value associated with each input audio signal; and

decode the bitstream into an approximation of the spatial audio, by using the first metadata parameters.

33. The decoder of claim 32 , wherein:

the representation of spatial audio further includes second metadata parameters being indicative of a downmix configuration for the input audio signals; and

the decoder is configured to decode the bitstream into an approximation of the spatial audio, by using the first and second metadata parameters.

34. The decoder of claim 33 , further comprising:

using a first metadata parameter is to restore an inter-channel time difference or adjusting a magnitude or a phase of a decoded audio output.

35. The decoder of claim 33 , further comprising:

using a second metadata parameter to determine an upmix matrix for recovery of a directional source signal or recovery of an ambient sound signal.

36. A renderer configured to:

receive a representation of spatial audio, the representation comprising:

a single- or multi-channel downmix audio signal created by downmixing input audio signals x from a plurality of microphones (m 1 , m 2 , m 3 ) in an audio capture unit capturing the spatial audio, wherein the downmixing is described by:

x=D·m

wherein:

D is a downmix matrix containing downmix coefficients defining weights for each input audio signal from the plurality of microphones, and

m is a matrix representing the input audio signals from the plurality of microphones, and

first metadata parameters associated with the downmix audio signal, wherein the first metadata parameters are indicative of one or more of: a relative time delay value, a gain value, and a phase value associated with each input audio signal; and

render the spatial audio using the first metadata.

37. The renderer of claim 36 , wherein:

the representation of spatial audio further includes second metadata parameters being indicative of a downmix configuration for the input audio signals; and

the renderer is configured to render spatial audio using the first and second metadata parameters.