Multichannel sub-band audio-signal processing using beamforming and echo cancellation
Provided are, among other things, systems, methods and techniques for audio-signal processing. One representative embodiment includes HT sub-band analysis/decomposition modules, e.g., one for each audio channel and one for an echo reference signal. Each HT sub-band analysis/decomposition module includes a Hilbert Transformation module and an analysis/decomposition filter bank and provides sub-band outputs. Echo-cancellation modules, e.g., one for each audio channel, perform echo-cancellation processing on such sub-bands. Beamforming modules, e.g., one for each sub-band, then perform beamforming, e.g., across all audio channels. Finally, a resynthesis stage combines the different sub-band outputs in order to provide a system output signal.
1. An audio-signal-processing system, comprising:
a plurality of Hilbert Transform (HT) sub-band analysis/decomposition modules, each including
(a) a Hilbert Transformation module having an input and an output that provides a Hilbert Transformed version of a signal at the input of said Hilbert Transformation module; and
(b) an analysis/decomposition filter bank having (i) an input coupled to the output of the Hilbert Transformation module and (ii) a plurality of outputs, each providing a different frequency sub-band for a signal provided at the input of said analysis/decomposition filter bank; and
a plurality of echo-cancellation modules, each having (i) a first set of sub-band inputs coupled to corresponding sub-band outputs of a unique one of the HT sub-band analysis/decomposition modules, (ii) a second set of sub-band inputs coupled to corresponding sub-band outputs of one of the HT sub-band analysis/decomposition modules that is common across said echo-cancellation modules, and (iii) sub-band outputs that result from performing echo-cancellation processing on said said first set of sub-band inputs, using said second set of sub-band inputs as reference signals;
a plurality of beamforming modules, each having a plurality of inputs and an output, wherein for each said beamforming module, the inputs of said beamforming module are coupled to a same one of the sub-bands output from different ones of said echo-cancellation modules, and the output of said beamforming module provides the same one of the sub-bands after beamforming; and
a resynthesis stage, having inputs coupled to the different sub-band outputs of the different beamforming modules, which resynthesizes said different sub-band outputs of said different beamforming modules in order to provide a system output signal.
2. An audio-signal-processing system according to claim 1 , further comprising a plurality of microphones coupled to inputs of said plurality of HT sub-band analysis/decomposition modules.
3. An audio-signal-processing system according to claim 2 , further comprising an echo reference signal coupled to an input of said common one of the plurality of HT sub-band analysis/decomposition modules.
4. An audio-signal-processing system according to claim 1 , wherein said resynthesis stage comprises (i) a plurality of sub-band resynthesis modules, each having an input coupled to the output of a different one of said beamforming modules and an output, and (ii) an adder having inputs coupled to the outputs of the sub-band resynthesis modules and an output coupled to an output of said resynthesis stage.
5. An audio-signal-processing system according to claim 4 , wherein each of said sub-band resynthesis modules comprises a first frequency shifter that shifts a current sub-band to a center frequency of 0 , followed by an up-sampler, followed by a low-pass filter, followed by a second frequency shifter that shifts a baseband signal back to an original center frequency of the current sub-band, followed by a resynthesis filter.
6. An audio-signal-processing system according to claim 5 , wherein only an in-phase portion of a signal output by said second frequency shifter is coupled to said resynthesis filter.
7. An audio-signal-processing system according to claim 1 , wherein said HT sub-band analysis/decomposition modules also shift individual sub-bands to a different center frequency and perform down-sampling.
8. An audio-signal-processing system according to claim 7 , wherein said down-sampling is by a factor of M/2, with M being a total number of different sub-bands provided by said analysis/decomposition filter bank.
9. An audio-signal-processing system according to claim 7 , wherein said different center frequency is a common frequency across all of said HT sub-band analysis/decomposition modules.
10. An audio-signal-processing system according to claim 9 , wherein said common frequency is π/M.
11. An audio-signal-processing system according to claim 1 , wherein said Hilbert Transformation module provides an in-phase output signal that is coupled to said analysis/decomposition filter bank and a quadrature output signal that is coupled to a second analysis/decomposition filter bank.
12. An audio-signal-processing system according to claim 11 , wherein said analysis/decomposition filter bank and said second analysis/decomposition filter bank simultaneously perform filtering and down-sampling.
13. An audio-signal-processing system according to claim 12 , wherein said down-sampling is performed at a factor of M/2, with M being a total number of different sub-bands provided by said analysis/decomposition filter bank and said second analysis/decomposition filter bank.
14. An audio-signal-processing system according to claim 13 , wherein outputs of said analysis/decomposition filter bank and said second analysis/decomposition filter bank are coupled to a frequency-shifting module.
15. An audio-signal-processing system according to claim 14 , wherein said frequency-shifting module shifts the sub-bands to a common center frequency.
16. An audio-signal-processing system according to claim 14 , wherein the frequency-shifting module multiplies complex-valued input values at time samples
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within each sub-band m by a factor of
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