Method and apparatus for playback of a higher-order ambisonics audio signal

Abstract

An advantage of Ambisonics representation is that the reproduction of the sound field can be adapted individually to nearly any given loudspeaker position arrangement. While facilitating a flexible and universal representation of spatial audio largely independent from loudspeaker setups, the combination with video playback on differently-sized screens may become distracting because the spatial sound playback is not adapted accordingly. The invention allows systematic adaptation of the playback of spatial sound field-oriented audio to its linked visible objects, by applying space warping processing as disclosed in EP 11305845.7. The reference size (or the viewing angle from a reference listening position) of the screen used in the content production is encoded and transmitted as metadata together with the content, or the decoder knows the actual size of the target screen with respect to a fixed reference screen size. The decoder warps the sound field in such a manner that all sound objects in the direction of the screen are compressed or stretched according to the ratio of the size of the target screen and the size of the reference screen.

Description

The advantage of stereo reverberation representation is that the reproduction of the sound field can be individually adapted to almost any given speaker placement arrangement. While the flexible and versatile representation that facilitates spatial audio is highly independent of speaker setup, combinations with audio playback on screens of different sizes can become fragmented because the spatial sound playback is not adapted accordingly. This invention allows for the systematic adaptation of spatial sound field audio playback to its linked visible objects by applying the spatial bending processing disclosed in EP11305845.7. The reference size of the screen used in content reproduction (or the viewing angle from the reference listening position) is encoded and transmitted as metadata along with the content, or the decoder knows the actual size of the target screen relative to a fixed reference screen size. The decoder bends the sound field by compressing or stretching all sound objects in the screen direction according to the ratio of the target screen size to the reference screen size. Abstract

Claims

1. A method for decoding an original Higher-Order Ambisonics audio signal denoted HOA and assigned to a video signal that is to be presented on a current screen but was generated for a reference screen, wherein the reference screen is an original and different screen, the method comprising: - decoding (83, 93) an input vector Ain of input HOA coefficients of said HOA signal so as to provide decoded audio signals sin in space domain for regularly positioned loudspeaker positions by calculating s in = Ψ 1 − 1 A in using the inverse Ψ 1 − 1 of a HOA mode matrix Ψ1; - determining reproduction adaptation information based on reference screen information (90) and the current screen, wherein the reference screen information includes information regarding a fixed reference screen size, wherein the reproduction adaption information is based on a difference of the reference screen and the current screen of their widths, and / or their heights, and / or their curvatures and wherein said reproduction adaptation information (90) controls warping such that for a current-screen watcher and listener of adapted decoded audio signals (91), a perceived position of the adapted decoded audio signals (91) corresponds with a perceived position of related video on said screen; - adapting said decoded (93) audio signals by warping (94) them in the space domain into an output vector Aout of adapted output HOA coefficients by calculating Aout = Ψ2 Sin, wherein the mode vectors of mode matrix ψ2 are modified according to a warping function by which the angles of the original loudspeaker positions for said reference screen are in the HOA coefficients output vector Aout mapped into the target angles of the target loudspeaker positions for the current screen.

2. The method of claim 1, further comprising outputting the adapted decoded audio signals to loudspeakers.

3. The method of claim 1 or 2, wherein the reproduction adaptation information (90) is received via a bitstream.

4. Apparatus for decoding an original Higher-Order Ambisonics audio signal denoted HOA and assigned to a video signal that is to be presented on a current screen but was generated for a reference screen, wherein the reference screen is an original and different screen, said apparatus including: - means (93) being adapted for decoding an input vector Ain of input HOA coefficients of said HOA signal so as to provide decoded audio signals sin in space domain for regularly positioned loudspeaker positions by calculating s in = Ψ 1 − 1 A in using the inverse Ψ 1 − 1 of a HOA mode matrix Ψ1; - means (90) being adapted for determining reproduction adaptation information based on reference screen information and the current screen, wherein the reference screen information includes information regarding a fixed reference screen size, wherein the reproduction adaption information is based on a difference of the reference screen and the current screen of their widths, and / or their heights, and / or their curvatures and wherein said reproduction adaptation information controls warping such that for a current-screen watcher and listener of adapted decoded audio signals (91), a perceived position of the adapted decoded audio signals (91) corresponds with a perceived position of related video on said screen; - adapting means (94) for adapting said decoded audio signals by warping them in the space domain into an output vector Aout of adapted output HOA coefficients by calculating Aout = Ψ2 sin, wherein the mode vectors of mode matrix Ψ2 are modified according to a warping function by which the angles of the original loudspeaker positions for said reference screen are in the HOA coefficients output vector Aout mapped into the target angles of the target loudspeaker positions for the current screen.

5. The apparatus of claim 4, comprising means being adapted for outputting the adapted decoded audio signals to loudspeakers.

6. The apparatus of claim 4 or 5, comprising means being adapted for receiving the reproduction adaptation information (90) via a bitstream.

7. The method of any one of claims 1 to 3, or apparatus of any one of claims 4 to 6, wherein said HOA signal contains multiple audio objects, assigned to corresponding video objects, and wherein for said current-screen watcher and listener the angle or distance of said audio objects would be different from the angle or distance, respectively, of said video objects on said reference screen.

8. The method of any one of claims 1 to 3 or 7, or apparatus of any one of claims 4 to 6 or 7, wherein in addition to said warping a weighting by a gain function (g(ϕ)) is carried out such that a resulting homogeneous sound amplitude per opening angle is obtained.

9. The method of any one of claims 1 to 3, 7 or 8, or apparatus of any one of claims 4 to 6, 7 or 8, wherein the reference screen size information comprises information regarding a width of the reference screen.

10. The method of any one of claims 1 to 3 or 7 to 9, or apparatus of any one of claims 4 to 6 or 7 to 9, wherein the reference screen size information comprises information regarding a height of the reference screen.

11. The method of any one of claims 1 to 3 or 7 to 10, or apparatus of any one of claims 4 to 6 or 7 to 10, wherein the reference screen size information comprises information regarding a centre of the reference screen.

12. The method of any one of claims 1 to 3 or 7 to 11, or apparatus of any one of claims 4 to 6 or 7 to 11, wherein the reference screen size information is provided in an angular format.

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