Method and apparatus for compressing and decompressing a higher order ambisonics signal representation
Higher Order Ambisonics (HOA) represents a complete sound field in the vicinity of a sweet spot, independent of loudspeaker set-up. The high spatial resolution requires a high number of HOA coefficients. In the invention, dominant sound directions are estimated and the HOA signal representation is decomposed into dominant directional signals in time domain and related direction information, and an ambient component in HOA domain, followed by compression of the ambient component by reducing its order. The reduced-order ambient component is transformed to the spatial domain, and is perceptually coded together with the directional signals. At receiver side, the encoded directional signals and the order-reduced encoded ambient component are perceptually decompressed, the perceptually decompressed ambient signals are transformed to an HOA domain representation of reduced order, followed by order extension. The total HOA representation is recomposed from the directional signals, the corresponding direction information, and the original-order ambient HOA component.
1. A method for compressing a Higher Order Ambisonics HOA signal representation, said method comprising:
estimating dominant directions;
decomposing or decoding the HOA signal representation into a number of dominant directional signals in time domain and related direction information, and a residual ambient component in HOA domain, wherein said residual ambient component represents the difference between said HOA signal representation and a representation of said dominant directional signals;
compressing said residual ambient component by reducing its order as compared to its original order;
transforming said residual ambient HOA component of reduced order to the spatial domain;
perceptually encoding said dominant directional signals and said transformed residual ambient HOA component.
2. The method according to claim 1 , wherein incoming vectors of HOA coefficients are framed into non-overlapping frames, and wherein a frame duration can be 25 ms.
3. The method according to claim 1 , wherein said dominant directions estimating is dependent on long overlapping groups of frames, such that for each current frame the content of adjacent frames is taken into consideration.
4. The method according to claim 1 , wherein said dominant directional signals and said transformed ambient HOA component are jointly perceptually compressed.
5. The method according to claim 1 , wherein said decomposing of the HOA signal representation into a number of dominant directional signals in time domain with related direction information and a residual ambient component in HOA domain is used for a signal-adaptive DirAC-like rendering of the HOA representation, wherein DirAC means Directional Audio Coding according to Pulkki.
6. The method according to claim 1 , wherein said dominant direction estimation is dependent on a directional power distribution of the energetically dominant HOA components.
7. A method for decompressing a Higher Order Ambisonics HOA signal representation that was compressed by:
estimating dominant directions;
decomposing or decoding the HOA signal representation into a number of dominant directional signals in time domain and related direction information, and a residual ambient component in HOA domain, wherein said residual ambient component represents the difference between said HOA signal representation and a representation of said dominant directional signals;
compressing said residual ambient component by reducing its order as compared to its original order;
transforming said residual ambient HOA component of reduced order to the spatial domain;
perceptually encoding said dominant directional signals and said transformed residual ambient HOA component, said method comprising:
perceptually decoding said perceptually encoded dominant directional signals and said perceptually encoded transformed residual ambient HOA component;
inverse transforming said perceptually decoded transformed residual ambient HOA component so as to get an HOA domain representation;
performing an order extension of said inverse transformed residual ambient HOA component so as to establish an original-order ambient HOA component;
composing said perceptually decoded dominant directional signals, said direction information and said original-order extended ambient HOA component so as to get an HOA signal representation.
8. An apparatus for compressing a Higher Order Ambisonics HOA signal representation, said apparatus comprising:
means adapted to estimate dominant directions;
means adapted to decompose or decode the HOA signal representation into a number of dominant directional signals in time domain and related direction information, and a residual ambient component in HOA domain, wherein said residual ambient component represents the difference between said HOA signal representation and a representation of said dominant directional signals;
means adapted to compress said residual ambient component by reducing its order as compared to its original order;
means adapted to transform said residual ambient HOA component of reduced order to the spatial domain;
means adapted to perceptually encode said dominant directional signals and said transformed residual ambient HOA component.
9. The apparatus according to claim 8 , wherein incoming vectors of HOA coefficients are framed into non-overlapping frames, and wherein a frame duration can be: 25 ms.
10. The apparatus according to claim 8 , wherein said dominant directions estimating is dependent on long overlapping groups of frames, such that for each current frame the content of adjacent frames is taken into consideration.
11. The apparatus according to claim 8 , wherein said dominant directional signals and said transformed ambient HOA component are jointly perceptually compressed.
12. The apparatus according to claim 8 , wherein said decomposing of the HOA signal representation into a number of dominant directional signals in time domain with related direction information and a residual ambient component in HOA domain is used for a signal-adaptive DirAC-like rendering of the HOA representation, wherein DirAC means Directional Audio Coding according to Pulkki.
13. The apparatus according to claim 8 , wherein said dominant direction estimation is dependent on a directional power distribution of the energetically dominant HOA components.
14. An apparatus for decompressing a Higher Order Ambisonics HOA signal representation that was compressed by:
estimating dominant directions;
decomposing or decoding the HOA signal representation into a number of dominant directional signals in time domain and related direction information, and a residual ambient component in HOA domain, wherein said residual ambient component represents the difference between said HOA signal representation and a representation of said dominant directional signals;
compressing said residual ambient component by reducing its order as compared to its original order;
transforming said residual ambient HOA component of reduced order to the spatial domain;
perceptually encoding said dominant directional signals and said transformed residual ambient HOA component, said apparatus comprising a decoder configured to:
perceptually decode said perceptually encoded dominant directional signals and said perceptually encoded transformed residual ambient HOA component;
inverse transform said perceptually decoded transformed residual ambient HOA component so as to get an HOA domain representation;
perform an order extension of said inverse transformed residual ambient HOA component so as to establish an original-order ambient HOA component;
compose said perceptually decoded dominant directional signals, said direction information and said original-order extended ambient HOA component so as to get an HOA signal representation.
15. An apparatus for compressing a Higher Order Ambisonics HOA signal representation, said apparatus comprising an encoder configured to:
estimate dominant directions;
decompose or decode the HOA signal representation into a number of dominant directional signals in time domain and related direction information, and a residual ambient component in HOA domain, wherein said residual ambient component represents the difference between said HOA signal representation and a representation of said dominant directional signals;
compress said residual ambient component by reducing its order as compared to its original order;
transform said residual ambient HOA component of reduced order to the spatial domain;
perceptually encode said dominant directional signals and said transformed residual ambient HOA component.
16. The apparatus according to claim 15 , wherein incoming vectors of HOA coefficients are framed into non-overlapping frames, and wherein a frame duration can be 25 ms.
17. The apparatus according to claim 15 , wherein said dominant directions estimating is dependent on long overlapping groups of frames, such that for each current frame the content of adjacent frames is taken into consideration.
18. The apparatus according to claim 15 , wherein said dominant directional signals and said transformed ambient HOA component are jointly perceptually compressed.
19. The apparatus according to claim 15 , wherein said decomposing of the HOA signal representation into a number of dominant directional signals in time domain with related direction information and a residual ambient component in HOA domain is used for a signal-adaptive DirAC-like rendering of the HOA representation, wherein DirAC means Directional Audio Coding according to Pulkki.
20. The apparatus according to claim 15 , wherein said dominant direction estimation is dependent on a directional power distribution of the energetically dominant HOA components.
21. An apparatus for decompressing a Higher Order Ambisonics HOA signal representation that was compressed by:
estimating dominant directions;
decomposing or decoding the HOA signal representation into a number of dominant directional signals in time domain and related direction information, and a residual ambient component in HOA domain, wherein said residual ambient component represents the difference between said HOA signal representation and a representation of said dominant directional signals;
compressing said residual ambient component by reducing its order as compared to its original order;
transforming said residual ambient HOA component of reduced order to the spatial domain;
perceptually encoding said dominant directional signals and said transformed residual ambient HOA component,
wherein said decompressing apparatus comprises a decoder configured to:
perceptually decode said perceptually encoded dominant directional signals and said perceptually encoded transformed residual ambient HOA component;
inverse transform said perceptually decoded transformed residual ambient HOA component so as to get an HOA domain representation;
perform an order extension of said inverse transformed residual ambient HOA component so as to establish an original-order ambient HOA component;
compose said perceptually decoded dominant directional signals, said direction information and said original-order extended ambient HOA component so as to get an HOA signal representation.
22. An HOA signal that is compressed according to the method of claim 1 .