Method and device for decoding an audio soundfield representation for audio playback
Soundfield signals as such e.g. Ambisonics carry a representation of a desired sound field. The Ambisonics format is based on spherical harmonic decomposition of the soundfield, and Higher Order Ambisonics uses spherical harmonics of at least 2 nd order. However, commonly used loudspeaker setups are irregular and lead to problems in decoder design. A method for improved decoding an audio soundfield representation for audio playback comprises calculating a panning function using a geometrical method based on the positions of a plurality of loudspeakers and a plurality of source directions, calculating a mode matrix Ξ from the loudspeaker positions, calculating a pseudo-inverse mode matrix μ + and decoding the audio soundfield representation. The decoding is based on a decode matrix that is obtained from the panning function and the pseudo-inverse mode matrix Ξ + .
1. A method for decoding an audio soundfield representation for audio playback, comprising steps of:
calculating, for each of a plurality of loudspeakers, a panning function using a geometrical method based on the positions of the loudspeakers and a plurality of source directions;
calculating a mode matrix Ξ N from the source directions;
calculating a pseudo-inverse mode matrix Ξ + of the mode matrix Ξ; and
decoding the audio soundfield representation, wherein the decoding is based on a decode matrix that is obtained from at least the panning function and the pseudo-inverse mode matrix Ξ + .
2. The method according to claim 1 , wherein the geometrical method used in the step of calculating a panning function is Vector Base Amplitude Panning (VBAP).
3. The method according to claim 1 , wherein the soundfield representation is an Ambisonics format of at least 2 nd order.
4. The method according to claim 1 , wherein the pseudo-inverse mode matrix Ξ + is obtained according to Ξ + =Ξ H [ΞΞ H ] −1 , wherein Ξ is the mode matrix of the plurality of source directions.
5. The method according to claim 4 , wherein the decode matrix is obtained according to D=WΞ H [ΞΞ H ] −1 =WΞ + , wherein W is the set of panning functions for each loudspeaker.
6. A device for decoding an audio soundfield representation for audio playback, comprising:
a first calculator for calculating, for each of a plurality of loudspeakers, a panning function using a geometrical method based on the positions of the loudspeakers and a plurality of source directions;
a second calculator for calculating a mode matrix Ξ from the source directions;
a third calculator for calculating a pseudo-inverse mode matrix Ξ + of the mode matrix Ξ; and
a decoder for decoding the soundfield representation, wherein the decoding is based on a decode matrix and the decoder means uses at least the panning function and the pseudo-inverse mode matrix Ξ + to obtain the decode matrix.
7. The device according to claim 6 , wherein the device for decoding further comprises a decode matrix calculation unit for calculating the decode matrix from the panning function and the pseudo-inverse mode matrix Ξ + .
8. The device according to claim 6 , wherein the geometrical method used in the step of calculating a panning function is Vector Base Amplitude Panning (VBAP).
9. The device according to claim 6 , wherein the soundfield representation is an Ambisonics format of at least 2 nd order.
10. The device according to claim 6 , wherein the pseudo-inverse mode matrix Ξ + is obtained according to Ξ + =Ξ H [ΞΞ H ] −1 , wherein Ξ is the mode matrix of the plurality of source directions.
11. The device according to claim 10 , wherein the decode matrix is obtained in a decode matrix calculation unit, according to D=W Ξ H [ΞΞ H ] −1 =WΞ + , wherein W is the set of panning functions for each loudspeaker.
12. A non-transitory computer readable medium having stored on it executable instructions to cause a computer to perform a method for decoding an audio soundfield representation for audio playback, the method comprising steps of:
calculating, for each of a plurality of loudspeakers, a panning function using a geometrical method based on the positions of the loudspeakers and a plurality of source directions;
calculating a mode matrix Ξ from the source directions;
calculating a pseudo-inverse mode matrix Ξ + of the mode matrix Ξ; and
decoding the audio soundfield representation, wherein the decoding is based on a decode matrix that is obtained from at least the panning function and the pseudo-inverse mode matrix Ξ + .
13. The computer readable medium according to claim 12 , wherein the geometrical method used in the step of calculating a panning function is Vector Base Amplitude Panning (VBAP).
14. The computer readable medium according to claim 12 , wherein the soundfield representation is an Ambisonics format of at least 2 nd order.
15. The computer readable medium according to claim 12 , wherein the pseudo-inverse mode matrix Ξ + is obtained according to Ξ + =Ξ H [ΞΞ H ] −1 , wherein Ξ is the mode matrix of the plurality of source directions.