Optimization of binaural sound spatialization based on multichannel encoding
The invention concerns sound spatialization with multichannel encoding for binaural reproduction on two loudspeakers, the spatial encoding being defined by encoding functions associated with multiple encoding channels and the decoding by applying filters for binaural reproduction. The invention provides for an optimization as follows: a) obtaining a original set of acoustic transfer functions particular to an individual's morphology (HRIR;HRTF), b) selecting spatial encoding functions (g(θ,φ,n)) and/or decoding filters (F(t,n)), and c) through successive iterations, optimizing the filters associated with the selected encoding functions or the encoding functions associated with the selected filters, or jointly the selected filters and encoding functions, by minimizing an error (c(HRIR,HRIR*)) calculated based on a comparison between: the original set of transfer functions (HRIR), and a set of reconstructed transfer functions (HRIR*) from encoding functions and decoding filters, whether optimized and/or selected.
1. A method of sound spatialization with a multichannel encoding and for reproduction on two loudspeakers, comprising a spatial encoding defined by encoding functions associated with a plurality of encoding channels and a decoding by applying filters for reproduction in a binaural context on the two loudspeakers, comprising:
a) obtaining an original suite of acoustic transfer functions specific to an individual's morphology, each transfer function in said original suite of acoustic transfer functions being associated with a position in space;
b) choosing, on the basis of at least one criterion of reduction of calculation complexity, to fix at least one of spatial encoding functions or decoding filters, and
c) through successive iterations, optimizing the filters associated with the chosen encoding functions fixed in b) or the encoding functions associated with the chosen filters fixed in b), or jointly the chosen filters and encoding functions, by minimizing an error calculated as a function of a comparison between:
the original suite of acoustic transfer functions, and
a suite of transfer functions reconstructed on the basis of the encoding functions and the decoding filters, optimized and/or chosen,
wherein the comparison in c) is calculated by, for each position in space associated with a transfer function in said original suite of acoustic transfer functions:
computing a first value being a moduli of said transfer function in said original suite of acoustic transfer functions;
computing a second value being a moduli of a transfer function in the suite of reconstructed transfer functions;
computing differences between the first value and the second value, expressed in the frequency domain and time independent.
2. The method as claimed in claim 1 , wherein the reconstructed suite of transfer functions is calculated by multiplying the filters by the encoding functions at each iteration.
3. The method as claimed in claim 2 , wherein, in b), spatial encoding functions are chosen which represent intensity panning laws based on virtual loudspeaker positions.
4. The method as claimed in claim 3 , wherein the positions of the virtual loudspeakers correspond to positions of a multichannel reproduction system with “surround” effect, the optimized decoding filters allowing a decoding of multichannel multimedia contents with “surround” effect for reproduction on two loudspeakers.
5. The method as claimed in claim 3 , wherein the encoding functions comprise a plurality of zero gains to be associated with encoding channels.
6. The method as claimed in claim 2 , wherein, in b), spatial encoding functions of the spherical harmonic type in an ambiophonic context are chosen.
7. The method as claimed in claim 1 , wherein interaural delay information is extracted, on the basis of the transfer functions obtained in a), while the optimization of the encoding functions and/or of the decoding filters is conducted on the basis of transfer functions from which said delay information has been extracted, said delay information being applied subsequently, on encoding.
8. The method as claimed in claim 1 , wherein interaural delay information is taken into account in the optimization of the decoding filters, and the spatial encoding is conducted without delay application.
9. The method as claimed in claim 1 , wherein, in b), some of the transfer functions obtained are chosen as decoding filters.
10. The method as claimed in claim 1 , wherein, for the first optimization iteration, the decoding filters are calculated by a solution of the pseudo-inverse type.
11. The method as claimed in claim 1 , wherein each difference is weighted as a function of a given direction in space so as to favor certain of said directions.
12. A sound spatialization system transforming a sound signal with a multichannel encoding and for reproduction on two loudspeakers, comprising a spatial encoding block defined by encoding functions associated with a plurality of encoding channels and a block for decoding by applying filters for reproduction in a binaural context on two loudspeakers, wherein the spatial encoding functions and/or the decoding filters are determined by implementing the method as claimed in claim 1 .
13. A computer program product comprising a non-transitory computer readable medium, having stored thereon a computer program comprising program instructions, the computer program being loadable into a data-processing unit and adapted to cause the data-processing unit to carry out the steps of claim 1 when the computer program is run by the data-processing unit.