Method and apparatus for decoding stereo loudspeaker signals from a higher order ambisonics audio signal
Decoding of Ambisonics representations for a stereo loudspeaker setup is known for first-order Ambisonics audio signals. But such first-order Ambisonics approaches have either high negative side lobes or poor localization in the frontal region. The invention deals with the processing for stereo decoders for higher-order Ambisonics HOA. The desired panning functions can be derived from a panning law for placement of virtual sources between the loudspeakers. For each loudspeaker a desired panning function for all possible input directions at sampling points is defined. The panning functions are approximated by circular harmonic functions, and with increasing Ambisonics order the desired panning functions are matched with decreasing error. For the frontal region between the loudspeakers, a panning law like the tangent law or vector base amplitude panning (VBAP) are used. For the rear directions panning functions with a slight attenuation of sounds from these directions are defined.
1. A method for decoding stereo loudspeaker signals from a three-dimensional higher-order Ambisonics audio signal, the method comprising:
receiving the three-dimensional higher-order Ambisonics audio signal;
determining, by at least one processor, a matrix G based on loudspeaker azimuth angle values and based on a number S of virtual sampling points on a sphere, wherein the matrix G contains desired panning function values for all virtual sampling points and wherein the loudspeaker azimuth angle values define corresponding loudspeaker positions;
determining, by the at least one processor, a matrix Ξ + based on the number S and an order N of the Ambisonics audio signal;
determining, by the at least one processor, a decoding matrix based on the matrices G and the mode matrix;
determining, by the at least one processor, the loudspeaker signals based on the decoding matrix and the higher-order Ambisonics audio signal; and
outputting the loudspeaker signals.
2. The method of claim 1 , wherein said panning functions are defined for multiple segments on the sphere, and for said segments different panning functions are used.
3. The method of claim 1 , wherein for the frontal region in-between the loudspeakers the tangent law or vector base amplitude panning VBAP is used as the panning law.
4. The method of claim 1 , wherein, for the directions to the back beyond the loudspeaker positions, panning functions with an attenuation of sounds from these directions are used.
5. The method of claim 1 , wherein more than two loudspeakers are placed on a segment of the sphere.
6. The method of claim 1 , wherein S=8N.
7. The method of claim 1 , wherein in case of equally distributed virtual sampling points said decoding matrix is replaced by a decoding matrix D=αGΞ H , wherein Ξ H is the adjoint of Ξ and a scaling factor α depends on the normalisation scheme of the circular harmonics and on s.
8. An apparatus for decoding stereo loudspeaker signals from a three-dimensional spatial higher-order Ambisonics audio signal, the apparatus comprising:
at least one input adapted to receive the three-dimensional spatial higher-order Ambisonics audio signal;
at least one processor a processor configured to
determine a matrix G based on loudspeaker azimuth angle values and based on a number S of virtual sampling points on a sphere, wherein the matrix G contains desired panning function values for all virtual sampling points and wherein the loudspeaker azimuth angle values define corresponding loudspeaker positions,
determine a matrix Ξ + based on the number S and an order N of the Ambisonics audio signal;
determine a decoding matrix based on the matrices G and the mode matrix;
determine the loudspeaker signals based on the decoding matrix and the higher-order Ambisonics audio signal;
at least one output configured to output the loudspeaker signals.
9. The apparatus of claim 8 , wherein said panning functions are defined for multiple segments on the sphere, and for said segments different panning functions are used.
10. The apparatus of claim 8 , wherein for the frontal region in-between the loudspeakers the tangent law or vector base amplitude panning VBAP is used as the panning law.
11. The apparatus of claim 8 , wherein, for the directions to the back beyond the loudspeaker positions, panning functions with an attenuation of sounds from these directions are used.
12. The apparatus of claim 8 , wherein more than two loudspeakers are placed on a segment of the sphere.
13. The apparatus of claim 8 , wherein S=8N.
14. The apparatus of claim 8 , wherein in case of equally distributed virtual sampling points said decoding matrix is replaced by a decoding matrix D=αGΞE H , wherein Ξ H is the adjoint of Ξ and a scaling factor α depends on the normalisation scheme of the circular harmonics and on S.