Room characterization and correction for multi-channel audio
View Patent ↗Devices and methods are adapted to characterize a multi-channel loudspeaker configuration, to correct loudspeaker/room delay, gain and frequency response or to configure sub-band domain correction filters.
1. A method of generating room correction filters for a multi-channel audio system, comprising:
providing a P-band oversampled analysis filter bank that downsamples an audio signal to base-band for a plurality P sub-bands and a P-band oversampled synthesis filter bank that upsamples the P sub-bands to reconstruct the audio signal where P is an integer;
providing a room spectral measure for each channel;
combining each said room spectral measure with a channel target curve to provide an aggregate spectral measure per channel;
for at least one channel,
extracting different portions of the aggregate spectral measure that correspond to different sub-bands;
remapping the extracted portion for each sub-band to base-band to form a remapped spectral measure for each sub-band to mimic the downsampling of the analysis filter bank, wherein remapping the extracted portions corresponding to an odd and even sub-bands comprises frequency shifting the extracted portion to base-band and translating the frequency shifted portion by minus and plus 90 degrees, respectively, thereby flipping part of the translated spectrum and producing a discontinuity in the remapped spectral measure for each sub-band;
independently estimating an auto regressive (AR) model to the remapped spectral measure for each sub-band; and
mapping coefficients of each said AR model to coefficients of a different minimum-phase all-zero sub-band correction filter; and
configuring P digital all-zero sub-band room correction filters from the corresponding coefficients that frequency correct the P base band audio signals between the analysis and synthesis filter banks.
2. The method of claim 1 , further comprising smoothing the discontinuity in the remapped spectral measure for each sub-band.
3. The method of claim 1 , wherein the P sub-bands are of uniform bandwidth and overlapping.
4. The method of claim 1 , wherein the room spectral measure has progressively less resolution at higher frequencies.
5. The method of claim 1 , wherein each said AR model is independently computed by,
computing an autocorrelation sequence as an inverse FFT of the remapped spectral measure; and
applying a Levinson-Durbin algorithm to the autocorrelation sequence to compute the AR model.
6. The method of claim 5 , wherein the Levinson-Durbin algorithm produces residual power estimates for the sub-bands, further comprising:
selecting an order for the correction filter based on the residual power estimate for the sub-band.
7. The method of claim 1 , wherein the channel target curve is a user selected target curve.
8. The method of claim 1 , further comprising applying frequency smoothing to the channel room spectral response to define the channel target curve.
9. The method of claim 1 , further comprising:
providing a common target curve for all said channels; and
applying correction to each correction filter to compensate for difference between the channel and common target curves.
10. The method of claim 9 , further comprising averaging the channel target curves to form the common target curve.
11. A method of generating room correction filters for a multi-channel audio system, comprising;
providing a P-band oversampled analysis filter bank that downsamples an audio signal to base-band for a plurality P sub-bands and a P-band oversampled synthesis filter bank that upsamples the P sub-bands to reconstruct the audio signal where P is an integer;
providing a room spectral measure for each channel;
combining each said room spectral measure with a channel target curve to provide an aggregate spectral measure per channel;
for at least one channel,
extracting different portions of the aggregate spectral measure that correspond to different sub-bands;
remapping the extracted portion for each sub-band to base-band to form a remapped spectral measure for each sub-band to mimic the downsampling of the analysis filter bank,
independently estimating an auto regressive (AR) model to the remapped spectral measure for each sub-band; and
mapping coefficients of each said AR model to coefficients of a different minimum-phase all-zero sub-band correction filter; and
configuring P digital all-zero sub-band room correction filters from the corresponding coefficients that frequency correct the P base band audio signals between the analysis and synthesis filter banks, wherein the room correction filters for higher frequency sub-bands are of progressively shorter length than the room correction filters for lower frequency sub-bands.
12. The method of claim 11 , wherein the minimum-phase sub-band filters of different length maintain a time-alignment of the P base-band audio signals such that delay is solely determined by delay in the analysis and synthesis filter banks.