Colorless generation of elevation perceptual cues using all-pass filter networks
A system includes one or more computing devices that encode spatial perceptual cues into a monaural channel to generate a plurality of output channels. A computing device determines a target amplitude response for the mid and side channels of the plurality of output channels, defining a spatial perceptual associated with one or more frequency-dependent phase shifts. The computing device determines a transfer function of a single-input, multi-output allpass filter based on the target amplitude response and determines coefficients of the allpass filter based on the transfer function, and processes the monaural channel with the coefficients of the allpass filter to generate the plurality of channels having the encoded spatial perceptual cues. The allpass filter is configured to be colorless with respect to the individual output channels, allowing for the placement of spatial cues into the audio stream to be decoupled from the overall coloration of the audio.
1. A method for encoding spatial cues along a sagittal plane into a monaural signal to generate a plurality of resulting channels, comprising, by a processing circuitry:
determining a target amplitude response for either mid- or side-components of the plurality of resulting channels based upon a spatial cue and corresponding to a coloration change in mid/side space, wherein the target amplitude response corresponds to a frequency-dependent phase shift that preserves coloration in left/right space;
converting the target amplitude response for either the mid or side components into a transfer function for a single-input, multi-output allpass filter; and
processing the monaural signal using the single-input, multi-output allpass filter, wherein the allpass filter is configured based upon the transfer function.
2. The method of claim 1 , wherein the target amplitude response for the mid- or side-component of the plurality of resulting channels is determined in terms of a notch.
3. The method of claim 2 , wherein the notch is in the range of 8 kHz to 16 kHz, for the purpose of encoding vertical spatial cues.
4. The method of claim 1 , wherein:
the target amplitude response for the mid- or side-component of the plurality of resulting channels is determined in terms of amplitude over frequency; and
further comprising converting the target amplitude response into coefficients for the single-input, multi-output allpass filter using an inverse discrete fourier transform (idft).
5. The method of claim 1 , wherein:
the target amplitude response for the mid- or side-component of the plurality of resulting channels is determined in terms of amplitude over frequency; and
further comprising converting the target amplitude response into coefficients for the single-input, multi-output allpass filter using a phase-vocoder.
6. The method of claim 1 , wherein the target amplitude response defines one or more parametric spatial cues, including one or more of a target broadband attenuation, a critical point, a filter characteristic, and a soundstage location.
7. The method of claim 6 , wherein the filter characteristic includes one of:
a high-pass filter characteristic;
a low-pass filter characteristic;
a band-pass filter characteristic; or
a band-reject filter characteristic.
8. A system for encoding spatial cues along a sagittal plane into a monaural signal to generate a plurality of resulting channels, comprising:
one or more computing devices configured to:
determine a target amplitude response for either mid- and side-components of the plurality of resulting channels based upon a spatial cue and corresponding to a coloration change in mid/side space, wherein the target amplitude response corresponds to a frequency-dependent phase shift that preserves coloration in left/right space;
convert the target amplitude response for either the mid or side components into a transfer function for a single-input, multi-output allpass filter; and
process the monaural signal using the single-input, multi-output allpass filter, wherein the allpass filter is configured based upon the transfer function.
9. The system of claim 8 , wherein the target amplitude response for the mid- or side-component of the plurality of resulting channels is determined in terms of a notch.
10. The system of claim 9 , wherein the notch is in the range of 8 kHz to 12 kHz, for the purpose of encoding vertical spatial cues.
11. The system of claim 8 , wherein:
the target amplitude response for the mid- or side-component of the plurality of resulting channels is determined in terms of amplitude over frequency; and
the one or more computing devices are further configured to convert the target amplitude response into coefficients for the single-input, multi-output allpass filter using an inverse discrete fourier transform (idft).
12. The system of claim 8 , wherein:
the target amplitude response for the mid- or side-component of the plurality of resulting channels is determined in terms of amplitude over frequency; and
the one or more computing devices are further configured to convert the target amplitude response into coefficients for the single-input, multi-output allpass filter using a phase-vocoder.
13. The system of claim 8 , wherein the target amplitude response defines one or more parametric spatial cues, including one or more of a target broadband attenuation, a critical point, a filter characteristic, and a soundstage location.
14. The system of claim 13 , wherein the filter characteristic includes one of:
a high-pass filter characteristic;
a low-pass filter characteristic;
a band-pass filter characteristic; or
a band-reject filter characteristic.
15. A non-transitory computer readable medium comprising stored instructions for encoding spatial cues along a sagittal plane into a monaural signal to generate a plurality of resulting channels, the instructions that, when executed by at least one processor, configure the at least one processor to:
determine a target amplitude response for either mid- and side-components of the plurality of resulting channels based upon a spatial cue and corresponding to a coloration change in mid/side space, wherein the target amplitude response corresponds to a frequency-dependent phase shift that preserves coloration in left/right space;
convert the target amplitude response for either the mid or side components into a transfer function for a single-input, multi-output allpass filter; and
process the monaural signal using the single-input, multi-output allpass filter, wherein the allpass filter is configured based upon the transfer function.
16. The non-transitory computer readable medium of claim 15 , wherein the target amplitude response for the mid- or side-component of the resulting channels is determined in terms of a notch.
17. The non-transitory computer readable medium of claim 16 , wherein the notch is in the range of 8 kHz to 12 kHz, for the purpose of encoding vertical spatial cues.
18. The non-transitory computer readable medium of claim 15 , wherein:
the target amplitude response for the mid- or side-component of the plurality of resulting channels is determined in terms of amplitude over frequency; and
the one or more processors are further configured to convert the target amplitude response into coefficients for the single-input, multi-output allpass filter using an inverse discrete fourier transform (idft).
19. The non-transitory computer readable medium of claim 15 , wherein:
the target amplitude response for the mid- or side-component of the plurality of resulting channels is determined in terms of amplitude over frequency; and
the one or more processors are further configured to convert the target amplitude response into coefficients for the single-input, multi-output allpass filter using a phase-vocoder.
20. The non-transitory computer readable medium of claim 15 , wherein the target amplitude response defines one or more constraints on a summation of the plurality of resulting channels, including one or more of a target broadband attenuation, a critical point, and a filter characteristic.