Method and device for decoding an audio soundfield representation
Soundfield signals such as 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 (HOA) 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 (W) 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 (Ξ + ) and decoding the audio soundfield representation. The decoding is based on a decode matrix (D) that is obtained from the panning function (W) and the pseudo-inverse mode matrix (Ξ + ).
1. A method for decoding an ambisonics audio soundfield representation for playback, the ambisonics audio soundfield representation having an order N, the method comprising:
receiving, by a processor configured to decode the audio soundfield representation, the audio soundfield representation;
receiving, by the processor, a decode matrix for decoding the audio soundfield representation to determine a decoded audio signal,
wherein the decode matrix is based on a mode matrix that was determined based on source directions and an order of the ambisonics audio soundfield representation;
wherein the decode matrix is further based on a second matrix containing panning functions for a first plurality of L loudspeaker positions and a second plurality of source directions, wherein a size of the second matrix is L×S, wherein the plurality of S source directions are distributed over a unit sphere, wherein each direction of the plurality of S source directions includes a corresponding azimuth angle and a corresponding inclination angle, and wherein S>=(N+1){circumflex over ( )}2, and wherein the panning functions are indicated by gain values; and
determining the decoded audio signal based on a multiplication of the decode matrix and the audio soundfield representation.
2. The method of claim 1 , wherein the decode matrix is predetermined.
3. A non-transitory computer readable medium having stored on it executable instructions to cause a computer to perform a method for decoding the ambisonics audio soundfield representation for audio playback according to claim 1 .
4. A system for decoding an ambisonics audio soundfield representation for playback, the ambisonics audio soundfield representation having an order N, the system comprising:
a receiver for receiving the audio soundfield representation;
a processor for receiving a decode matrix for decoding the audio soundfield representation to determine a decoded audio signal,
wherein the decode matrix is based on a mode matrix that was determined based on source directions and an order of the ambisonics audio soundfield representation;
wherein the decode matrix is further based on a second matrix containing panning functions for a first plurality of L loudspeaker positions and a second plurality of S source directions, wherein a size of the second matrix is L×S, wherein the plurality of S source directions are distributed over a unit sphere, wherein each direction of the plurality of S source directions includes a corresponding azimuth angle and a corresponding inclination angle, and wherein S>=(N+1){circumflex over ( )}2, and wherein the panning functions are indicated by gain values; and
a decoder for determining the decoded audio signal based on a multiplication of the decode matrix and the audio soundfield representation.