Noise-reduction processing of speech signals
View Patent ↗The present invention relates to a method for signal processing comprising the steps of providing a set of prototype spectral envelopes, providing a set of reference noise prototypes, wherein the reference noise prototypes are obtained from at least a sub-set of the provided set of prototype spectral envelopes, detecting a verbal utterance by at least one microphone to obtain a microphone signal, processing the microphone signal for noise reduction based on the provided reference noise prototypes to obtain an enhanced signal and encoding the enhanced signal based on the provided prototype spectral envelopes to obtain an encoded enhanced signal.
1. A method for signal processing comprising:
obtaining a set of common reference noise prototypes from at least a sub-set of a set of prototype spectral envelopes;
processing a microphone signal characterizing a verbal utterance for noise reduction to obtain an enhanced signal, the processing being based on the set of common reference noise prototypes; and
encoding the enhanced signal to obtain an encoded enhanced signal, the encoding being based on the set of common reference noise prototypes.
2. The method according to claim 1 , further comprising transmitting the encoded enhanced signal to a remote party;
receiving the transmitted encoded enhanced signal by the remote party; and
decoding the received signal by the remote party.
3. The method according to claim 1 , wherein the set of prototype spectral envelopes is used for encoding the enhanced signal in speech pauses detected in the microphone signal or when a signal-to-noise ratio of the microphone signal falls below a predetermined threshold.
4. The method according claim 1 , wherein the common reference noise prototypes are spectral envelopes modeled by an all-pole filter function.
5. The method according to claim 1 , wherein the processing of the microphone signal for noise reduction comprises:
estimating the power density of a noise contribution in the microphone signal;
matching the spectrum of the noise contribution obtained from the estimated power density of the noise contribution with the set of common reference noise prototypes to find the best matching reference noise prototype; and
using the best matching reference noise prototype to determine maximum damping factors for noise reduction of the microphone signal.
6. The method according to claim 5 , wherein the processing of the microphone signal for noise reduction is performed by a Wiener-like filtering module comprising damping factors obtained based on the best matching reference noise prototype, the power density spectrum of sub-band signals obtained from the microphone signal and the estimated power density spectrum of the background noise.
7. The method according to claim 5 , wherein the spectrum of the noise contribution obtained from the estimated power density of the noise contribution is matched only with a subset of the set of common reference noise prototypes within a predetermined frequency range.
8. A method according to claim 1 , wherein the microphone is part of a hands-free set installed in a vehicle and wherein at least one of the set of common reference noise prototypes on which the processing of the microphone signal for noise reduction to obtain an enhanced signal is determined from a sub-set of the set of common reference noise prototypes that is selected according to a current traveling speed of the vehicle, in particular, the automobile; and/or
the set of common reference noise prototypes is obtained from a sub-set of the provided set of prototype spectral envelopes selected according to the type of the vehicle, in particular, the automobile.
9. A computer program product comprising a non-transitory computer readable medium having computer executable computer code thereon for processing a microphone signal, the computer code comprising:
computer code for obtaining a set of common reference noise prototypes from at least a sub-set of prototype spectral envelopes;
computer code for processing a microphone signal characterizing a verbal utterance for noise reduction to obtain an enhanced signal, the processing being based on the set of common reference noise prototypes; and
computer code for encoding the enhanced signal to obtain an encoded enhanced signal, the processing being based on the set of common reference noise prototypes.
10. The computer program product according to claim 9 , further comprising
computer code for transmitting the encoded enhanced signal to a remote party;
computer code for receiving the transmitted encoded enhanced signal by the remote party; and
computer code for decoding the received signal by the remote party.
11. The computer program product according to claim 9 , wherein the set of prototype spectral envelopes is used for encoding the enhanced signal in speech pauses detected in the microphone signal or when a signal-to-noise ratio of the microphone signal falls below a predetermined threshold.
12. The computer program product according claim 9 , wherein the set of common reference noise prototypes are spectral envelopes modeled by an all-pole filter function.
13. The method according to claim 9 , wherein the computer code for processing of the microphone signal for noise reduction includes:
computer code for estimating the power density of a noise contribution in the microphone signal;
computer code for matching the spectrum of the noise contribution obtained from the estimated power density of the noise contribution with the set of common reference noise prototypes to find the best matching reference noise prototype; and
computer code for using the best matching reference noise prototype to determine maximum damping factors for noise reduction of the microphone signal.
14. The computer program product according to claim 13 , wherein the computer code for processing of the microphone signal for noise reduction is performed using a Wiener-like filter comprising damping factors obtained based on the best matching reference noise prototype, the power density spectrum of sub-band signals obtained from the microphone signal and the estimated power density spectrum of the background noise.
15. The computer program product according to claim 13 , wherein the spectrum of the noise contribution obtained from the estimated power density of the noise contribution is matched only with a subset of the set of common reference noise prototypes within a predetermined frequency range.
16. A computer program product according to claim 9 , wherein at least one of the set of common reference noise prototypes on which the processing of the microphone signal for noise reduction to obtain an enhanced signal is based is determined from a sub-set of the set of common reference noise prototypes that is selected according to a current traveling speed of the vehicle, in particular, the automobile; and/or
the set of common reference noise prototypes is obtained from a sub-set of the set of prototype spectral envelopes selected according to the type of the vehicle, in particular, the automobile.
17. A signal processing system comprising:
an encoding database comprising prototype spectral envelopes;
a reference database comprising common reference noise prototypes, wherein the reference noise prototypes are obtained from at least a sub-set of the set of prototype spectral envelopes; and
a noise reduction filtering module configured to process a microphone signal comprising background noise to obtain an enhanced microphone signal, the processing being based on the set of common reference noise prototypes; and
an encoder configured to encode the enhanced microphone signal, the encoding being based on the set of common reference noise prototypes.
18. The signal processing system according to claim 17 , further comprising
a noise estimating module configured to estimate the power density of a background noise contribution of the microphone signal;
a matching module configured to match the spectrum of the noise contribution obtained from the estimated power density of the noise contribution with the set of common reference noise prototypes comprised in the reference database to find the best matching reference noise prototype; and wherein
the noise reduction filtering module is configured to use the best matching reference noise prototype for noise reduction of the microphone signal.
19. The signal processing system according to claim 17 , wherein the noise reduction filtering module uses a Wiener-like filter comprising damping factors obtained based on the best matching reference noise prototype, the power density spectrum of microphone sub-band signals obtained from the microphone signal and the estimated power density spectrum of the background noise.
20. The signal processing system according to claim 17 , wherein the noise reduction filtering module is configured to operate in the sub-band regime and to output noise-reduced microphone sub-band signals; and further comprising
an analysis filter bank configured to process the microphone signal to obtain microphone sub-band signals and to provide the microphone sub-band signals to the noise reduction filtering module; and
a synthesis filter bank configured to process the noise-reduced microphone sub-band signals to obtain a noise-reduced full-band microphone signal in the time domain.
21. The signal processing system according to one of the claims 17 , wherein the signal processing system is installed in an automobile and the reference database is derived from the encoding database dependent on type of the automobile.
22. The signal processing system according claim 17 , further comprising:
a control module configured to control determination of at least one of the set of common reference noise prototypes used by the noise reduction filtering module to process the microphone signal to obtain the enhanced microphone signal based on a current traveling speed of the automobile.