Noise spectrum tracking in noisy acoustical signals

A system for estimating noise power spectral density PSD in an input sound signal comprising a noise signal part and a target signal part, comprising:

• a unit for providing a digitized electrical input signal according to the input sound signal to a control path;
• a memory device for storing a number of time frames of the digitized electrical input signal each comprising a predefined number N2 of digital time samples xn where n=1, 2, . . . , N2, corresponding to a frame length in time of L2=N2/fs where fs is a predefined sampling frequency;
• a time to frequency transformation unit for transforming the stored time frames on a frame by frame basis to provide a corresponding spectrum Y of frequency samples;
• a first processing unit for deriving a periodogram comprising an energy content |Y|2 from the corresponding spectrum Y for each frequency sample in the corresponding spectrum, the energy content being an energy of a sum of the noise signal part and the target signal part;
• a gain unit for applying a gain function G(k,m) to each frequency sample of the corresponding spectrum where k is frequency bin index-number and m is time-frame index-number, thereby estimating a noise energy level |Ŵ|2 in each frequency sample, |Ŵ|2=G(k,m)·|Y|2, where
• G(k,m)=f(σS2(k,m), σW2(k,m−1), |Y(k,m)|2), where f is an arbitrary function of σS2, σW2, and |Y|2, where σS2 is a speech PSD and σW2 the noise PSD based on frames of said time to frequency transformation unit;
• a second processing unit for dividing the corresponding spectrum into a number Nsb2 of sub-bands, each sub-band comprising a predetermined number nsb2 of frequency samples;
• a first estimating unit for providing a first estimate |{circumflex over (N)}|2 of the noise PSD level in the sub-band based on a non-zero noise energy level |Ŵ|2 of each of the frequency samples in the sub-band, assuming that the noise PSD level is constant across the sub-band;
• and
• a second estimating unit for providing a second, improved estimate |Ñ|2 of the noise PSD level in the sub-band by applying a bias compensation factor B to the first estimate, |Ñ|2=B·|{circumflex over (N)}|2.

A non-transitory computer readable medium storing a computer program comprising instructions for causing a data processing system to perform a method when said instructions are executed on the data processing system, the method comprising:

• d) providing a digitized electrical input signal to a control path;
• d1) storing a number of time frames of the digitized electrical input signal each comprising a predefined number N2 of digital time samples xn where n=1, 2, . . . , N2, corresponding to a frame length in time of L2=N2/fs where fs is a predefined sampling frequency;
• d2) performing a time to frequency transformation of the stored time frames on a frame by frame basis to provide a corresponding spectrum Y of frequency samples;
• d3) deriving a periodogram comprising an energy content |Y|2 from the corresponding spectrum Y, for each frequency sample in the corresponding spectrum, the energy content being an energy of a sum of the noise signal part and the target signal part;
• d4) applying a gain function G(k,m) to each frequency sample of the corresponding spectrum where k is frequency bin index-number and m is time-frame index-number, thereby estimating a noise energy level |Ŵ|2 in each frequency sample, |Ŵ|2=G(k,m)·|Y|2, where
• G(k,m)=f(σS2(k,m),σW2(k,m−1),|Y(k,m)|2), where f is an arbitrary function of σS2, σW2, and |Y|2, where σS2 is a speech PSD and σW2 the noise PSD based on frames of said time to frequency transformation;
• d5) dividing the corresponding spectrum into a number Nsb2 of sub-bands, each sub-band comprising a predetermined number nsb2 of frequency samples, and assuming that a noise PSD level is constant across a sub-band;
• d6) providing a first estimate |{circumflex over (N)}|2 of the noise PSD level in the sub-band based on non-zero estimated noise energy level |Ŵ|2 of each of the frequency samples in the sub-band;
• and
• d7) providing a second, improved estimate |Ñ|2 of the noise PSD level in the sub-band by applying a bias compensation factor B to the first estimate, |Ñ|2=B·|{circumflex over (N)}|2.

A method of estimating noise power spectral density PSD in an input sound signal produced by one or more microphones and generating an output for noise reduction of the input sound signal, the input sound signal comprising a noise signal part and a target signal part, the method comprising:

• d) providing a digitized electrical input signal according to the input sound signal to a control path and processing the digitized electrical input signal in the control path comprising
• d1) storing a number of time frames of the digitized electrical input signal each comprising a predefined number N2 of digital time samples xn where n=1, 2, . . . , N2, corresponding to a frame length in time of L2=N2/fs where fs is a predefined sampling frequency;
• d2) performing a time to frequency transformation of the stored time frames on a frame by frame basis to provide a corresponding spectrum Y of frequency samples;
• d3) deriving a periodogram comprising an energy content |Y|2 from the corresponding spectrum Y, for each frequency sample in the corresponding spectrum, the energy content being an energy of a sum of the noise signal part and the target signal part;
• d4) applying a gain function G(k,m) to each frequency sample of the corresponding spectrum where k is frequency bin index-number and m is time-frame index-number, thereby estimating a noise energy level |Ŵ|2 in each frequency sample, |Ŵ|2=G(k,m)·|Y|2, where
• G(k,m)=f(σS2(k,m),σW2(k,m−1),|Y(k,m)|2), where f is an arbitrary function of two or more of σS2, σW2, and |Y|2 , where σS2 is a speech PSD and σW2 the noise PSD based on frames of said time to frequency transformation;
• d5) dividing the corresponding spectrum into a number Nsb2 of sub-bands, each sub-band comprising a predetermined number nsb2 of frequency samples, and assuming that a noise PSD level is constant across a sub-band;
• d6) providing a first estimate |{circumflex over (N)}|2 of the noise PSD level in the sub-band based on a non-zero estimated noise energy level |Ŵ|2 of each of the frequency samples in the sub-band;
• and
• d7) providing a second, improved estimate |Ñ|2 of the noise PSD level in the sub-band by applying a bias compensation factor B to the first estimate, |Ñ|2=B·|Ñ|2, as the output for noise reduction of the input sound signal.

A method of estimating noise power spectral density PSD in an input sound signal produced by one or more microphones and generating an output for noise reduction of the input sound signal, the input sound signal comprising a noise signal part and a target signal part, the method comprising:

• a1) converting the input sound signal to an electrical input signal according to the input sound signal;
• a2) sampling the electrical input signal with a predefined sampling frequency fs to provide a digitized electrical input signal comprising digital time samples xn;
• b1) processing the digitized electrical input signal in a relatively low latency signal path, the processing in the relatively low latency signal path including
• c1) storing a number of time frames of the digitized electrical input signal each comprising a predefined number N1 of digital time samples xn where n=1, 2, . . . , N1, corresponding to a frame length in time of Li=N1/fs;
• c2) performing a time to frequency transformation of the stored time frames on a frame by frame basis to provide a corresponding spectrum X of frequency samples;
• and
• c5) dividing the corresponding spectrum X into a number Nsb1 of sub-bands, each sub-band comprising a predetermined number nsb1 of frequency samples;
• d1) providing the digitized electrical input signal to a control path;
• d2) processing the digitized electrical input signal in the control path, the processing in the control path including;
• d3) storing a number of time frames of the digitized electrical input signal each comprising a predefined number N2 of digital time samples xn where n=1, 2, . . . , N2, corresponding to a frame length in time of L2=N2/fs where fs is the predefined sampling frequency wherein the frame length L2 of the control path is larger than the frame length L1 of the signal path;
• d4) performing a time to frequency transformation of the stored time frames stored in the step d3on a frame by frame basis to provide a corresponding spectrum Y of frequency samples;
• d5) deriving a periodogram comprising an energy content |Y|2 from the corresponding spectrum Y, for each frequency sample in the corresponding spectrum Y, the energy content being an energy of a sum of the noise signal part and the target signal part;
• d6) applying a gain function G(k,m) to each frequency sample of the corresponding spectrum Y where k is frequency bin index-number and m is time-frame index-number, thereby estimating a noise energy level |Ŵ|2 in each frequency sample, |Ŵ|2=G(k,m)·|Y|2;
• d7) dividing the corresponding spectrum Y into a number Nsb2 of sub-bands, each sub-band comprising a predetermined number nsb2 of frequency samples, and assuming that a noise PSD level is constant across a sub-band;
• d8) providing a first estimate |{circumflex over (N)}|2 of the noise PSD level in the sub-band based on a non-zero estimated noise energy level |Ŵ|2 of each of the frequency samples in the sub- band;
• and
• d9) providing a second, improved estimate |Ñ|2 of the noise PSD level in the sub-band by applying a bias compensation factor B to the first estimate, |Ñ|2=B·|Ñ|2, as the output for noise reduction of the input sound signal.