Method and apparatus for conversion between multi-channel audio formats

1. Apparatus for conversion of an input multi-channel representation into a different output multi-channel representation of a spatial audio signal, comprising:

an analyzer configured for deriving an intermediate representation of the spatial audio signal, the intermediate representation comprising direction parameters indicating a direction of origin of a portion of the spatial audio signal and at least one downmix channel; and

a signal composer configured for generating the output multi-channel representation of the spatial audio signal using the intermediate representation of the spatial audio signal by performing an upmixing operation, wherein the at least one downmix channel and the direction parameters are used in the upmixing operation.

2. Apparatus in accordance with claim 1 , in which the analyzer is operative to derive direction parameters depending on a virtual correlation of audio channels associated to the input multi-channel representation.

3. Apparatus in accordance with claim 1 , in which the analyzer is operative to derive direction parameters preserving the relative phase information of audio channels associated to the input multi-channel representation.

4. Apparatus in accordance with claim 1 , in which the analyzer is operative to derive different direction parameters for finite width frequency portions of the spatial audio signal.

5. Apparatus in accordance with claim 1 , in which the analyzer is operative to derive different direction parameters for finite length time portions of the spatial audio signal.

6. Apparatus in accordance with claim 4 , in which the analyzer is operative to derive the different direction parameters for finite length time portions of the spatial audio signal associated to the frequency portions, wherein the length of a first time portion associated to a first frequency portion differs from the length of a second time portion association to a second, different frequency portion of the spatial audio signal.

7. Apparatus in accordance with claim 1 , in which the analyzer is operative to derive direction parameters describing a vector pointing to the direction of origin of the portion of the spatial audio signal.

8. Apparatus in accordance with claim 1 , in which the analyzer is additionally operative to derive one or more audio channels associated to the intermediate representation.

9. Apparatus in accordance with claim 8 , in which the analyzer is operative to derive audio channels corresponding to loudspeakers associated to the input multi-channel representation.

10. Apparatus in accordance with claim 8 , in which the analyzer is operative to derive one downmix channel as sum of audio channels corresponding to loudspeakers associated to the input multi-channel representation.

11. Apparatus in accordance with claim 8 , in which the analyzer is operative to derive at least one audio channel associated to the direction of an axis of a Cartesian Coordinate System.

12. Apparatus in accordance with claim 11 , in which the analyzer is operative to derive the at least one audio channel building the weighted sum of audio channels corresponding to loudspeakers associated to the input multi-channel representation.

13. Apparatus in accordance with claim 11 , in which the analyzer is operative such that the deriving of the at least one audio channel X associated to the direction V of an axis of the Cartesian Coordinate System can be described by a combination of n audio channels C n corresponding to all n loudspeakers associated to the input multi-channel representation and directed in a direction C n , according to the following formula:

X

=

∑

n

=

1

N

⁢

C

n

·

cos

⁡

(

angle

⁡

(

L

n

,

V

)

)

.

14. Apparatus in accordance with claim 1 , in which the analyzer is further operative to derive a diffuseness parameter indicating a diffuseness of the direction of origin of the portion of the spatial audio signal.

15. Apparatus in accordance with claim 1 , in which the signal composer is operative to distribute the portion of the spatial audio signal to a number of channels corresponding to a number of loudspeakers associated to the output multi-channel representation.

16. Apparatus in accordance with claim 15 , in which the signal composer is operative such that the portion of the spatial audio signal is distributed with greater intensity to a channel corresponding to a loudspeaker closer to the direction indicated by the direction parameters than to a channel corresponding to a loudspeaker further away from that direction.

17. Apparatus in accordance with claim 14 , in which the signal composer is operative such that the portion of the spatial audio signal is distributed with more uniform intensity to channels corresponding to loudspeakers associated to the output multi-channel representation when the diffuseness parameter indicates higher diffuseness than when the diffuseness parameter indicates lower diffuseness.

18. Apparatus in accordance with claim 1 further comprising:

an input interface for receiving the input multi-channel representation.

19. Apparatus in accordance with claim 1 further comprising:

an input representation decoder for deriving a number of audio channels corresponding to all loudspeakers associated to the input multi-channel representation.

20. Apparatus in accordance with claim 15 , in which the signal composer further comprises an output channel encoder for deriving the output multi-channel representation based on the audio channels corresponding to the loudspeakers associated to the output channel representation.

21. Apparatus in accordance with claim 1 further comprising an output interface for providing the output multi-channel representation.

22. Method for conversion of an input multi-channel representation into a different output multi-channel representation of a spatial audio signal, the method comprising:

deriving an intermediate representation of the spatial audio signal, the intermediate representation comprising direction parameters indicating a direction of origin of a portion of the spatial audio signal and at least one downmix channel; and

generating the output multi-channel representation of the spatial audio signal using the intermediate representation of the spatial audio signal by performing an upmixing operation, wherein the at least one downmix channel and the direction parameters are used in the upmixing operation.

23. A non-transitory storage medium having stored thereon a computer program for, when running on a computer, implementing a method for conversion of a multi-channel representation into a different output multi-channel representation of a spatial audio signal, the method comprising:

deriving an intermediate representation of the spatial audio signal, the intermediate representation comprising direction parameters indicating a direction of origin of a portion of the spatial audio signal and at least one downmix channel; and

generating the output multi-channel representation of the spatial audio signal using the intermediate representation of the spatial audio signal by performing an upmixing operation, wherein the at least one downmix channel and the direction parameters are used in the upmixing operation.