Audio object encoding and decoding

1. An audio object encoder comprising:

a receiver configured to receive N audio objects;

a mixer configured to mix the N audio objects to produce M first audio channels;

a channel circuit configured to derive K second audio channels from the M first audio channels where K=1 or 2 and K<M, wherein each of the M first audio channels is represented in at least one of the K second audio channels;

a parameter circuit configured to generate audio object upmix parameters for at least part of each of the N audio objects relative to the K second audio channels, the upmix parameters describing how the N audio objects may be generated from the K second audio channels; and

an output circuit configured to generate an output data stream comprising the audio object upmix parameters and the M first audio channels, wherein the output data stream does not include any of the K second audio channels.

2. The audio object encoder of claim 1 wherein the channel circuit is configured to derive the K second audio channels by downmixing the M first audio channels.

3. The audio object encoder of claim 1 wherein the channel circuit is configured to derive the K second audio channels by selecting a K second audio channel subset of the M first audio channels.

4. The audio object encoder of claim 1 wherein the output data stream comprises a multichannel encoded data stream for the M first audio channels, and the audio object upmix parameters are comprised in a part of the multichannel encoded data stream.

5. The audio object encoder of claim 1 wherein the output circuit is configured to include mixing data representative of the mixing of the N audio objects to the M first audio channels in the output data stream.

6. An audio object decoder comprising:

a receiver receiving a data stream comprising audio data for an M first audio channel mix of N audio objects and audio object mix parameters for the N audio objects relative to K second audio channels where K=1 or 2 and K<M, wherein each of the M audio channels is presented in at least one of the K audio channels and the output data stream does not include any of the K audio channels;

a channel circuit deriving K second audio channels from the M channel mix; and

an object decoder generating P audio signals from N audio objects at least partially generated by upmixing the K second audio channels based on the audio object upmix parameters.

7. The audio object decoder of claim 6 wherein the channel circuit is configured to derive the K second audio channels by downmixing the M first audio channels.

8. The audio object decoder of claim 7 wherein the data stream comprises downmix data indicative of an encoder downmixing from M first audio channels to K second audio channels, and wherein the channel circuit is configured to adapt the downmixing in response to the downmix data.

9. The audio object decoder of claim 7 wherein the channel circuit is configured to derive the K second audio channels by selecting a K second audio channel subset of the M first audio channels.

10. The audio object decoder of claim 9 wherein the data stream comprises additional audio object upmix parameters for the N audio objects relative to L third audio channels where L=1 or 2 and L<M, and the L third audio channels and the K second audio channels are different subsets of the M first audio channels, and wherein the object decoder is further configured to generate the P signals from N audio objects at least partially generated by upmixing the L third audio channels based on the additional audio object upmix parameters.

11. The audio object decoder of claim 10 wherein at least one of the P signals is generated by combining contributions from both the upmixing of the K second audio channels based on the audio object upmix parameters and the upmixing of the L third audio channels based on the additional audio object upmix parameters.

12. The audio object decoder of claim 6 wherein the data stream comprises mix data representative of the mixing of the N audio objects to the M first audio channels, and wherein the object decoder is arranged to generate residual data for at least a subset of the N audio objects in response to the mix data and the audio object upmix parameters, and to generate the P audio signals in response to the residual data.

13. A method of operating an audio object encoder comprising:

in an audio object encoder:

receiving in a receiver, N audio objects;

mixing in a mixer the N audio objects to produce M first audio channels;

deriving in a channel circuit, K second audio channels from the M first audio channels where K=1 or 2 and K<M, wherein each of the M first audio channels is represented in at least one of the K second audio channels;

generating in parameter circuit audio object upmix parameters for at least part of each of the N audio objects relative to the K second audio channels, the upmix parameters describing how the N audio objects may be generated from the K audio channels; and

generating via an output circuit, an output data stream comprising the audio object upmix parameters and the M audio channels, wherein the output data stream does not include any of the K audio channels.

14. A computer program product, stored on a medium that is not a transitory propagating wave or signal, the program product comprising computer program code, which when accessed by an audio object encoder causes the encoder to execute the acts of claim 13 .

15. A method of operating an audio object decoder comprising:

in an audio object encoder:

receiving into a receiver, a data stream comprising audio data for an M first channel mix of N audio objects and audio object upmix parameters for the N audio objects relative to K second audio channels where K=1 or 2 and K<M, wherein each of the M first audio channels is presented in at least one of the K second audio channels and the output data stream does not include any of the K second audio channels;

deriving in a channel circuit, K second audio channels from the M first channel mix; and

generating in an object decoder, P audio signals from the N audio objects, the P audio signals at least partially generated by upmixing the K second audio channels based on the audio object upmix parameters.

16. A computer program product, stored on a medium that is not a transitory propagating wave or signal, the program product comprising computer program code, which when accessed by an audio object decoder causes the decoder to execute the acts of claim 15 .