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 over a plurality of loudspeakers, the method comprising:
receiving a decoding matrix that is based on a first matrix and a base matrix, wherein the first matrix includes gain vectors that are based on a panning based on positions of the loudspeakers and a plurality of source directions, wherein the panning is obtained based on a Vector Base Amplitude Panning (VBAP), wherein the source directions are distributed evenly over a unit sphere, a number of the source directions is S, the order of the ambisonics audio soundfield representation is N, and S>(N+1){circumflex over ( )}2, and wherein the base matrix is determined based on the first matrix and a mode matrix determined based on the source directions and an order of the ambisonics audio soundfield representation; and
decoding the ambisonics audio soundfield representation with the decoding matrix.
2. An apparatus for decoding an ambisonics audio soundfield representation for playback over a plurality of loudspeakers, the apparatus comprising:
a receiver for receiving a decoding matrix that is based on a first matrix and a base matrix, wherein the first matrix includes gain vectors that are based on a panning based on positions of the loudspeakers and a plurality of source directions, wherein the panning is obtained based on a Vector Base Amplitude Panning (VBAP), wherein the source directions are distributed evenly over a unit sphere, a number of the source directions is S, the order of the ambisonics audio soundfield representation is N, and S>(N+1){circumflex over ( )}2, and wherein the base matrix is determined based on the first matrix and a mode matrix determined based on the source directions and an order of the ambisonics audio soundfield representation; and
a decoder for decoding the ambisonics audio soundfield representation with the decoding matrix.
3. A non-transitory computer readable medium having stored on it executable instructions to cause a computer to perform the method of claim 1 .
4. The method of claim 1 , wherein the ambisonics soundfield representation is of at least a 2nd order.
5. The apparatus of claim 2 , wherein the ambisonics soundfield representation is of at least a 2nd order.