Patent ID: 8712074

Claim:
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 to a control path according to the input sound signal and processing the digitalized electrical input signal in the control path including d1) storing a number of time frames of the digitized electrical input signal each comprising a predefined number N 2 of digital time samples x n where n=1, 2, . . . , N 2 , corresponding to a frame length in time of L 2 =N 2 /f s where f s 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(σ S 2 (k,m), σ W 2 (k,m−1), |Y(k,m)| 2 ), where f is an arbitrary function of σ S 2 , σ W 2 , and |Y| 2 , where σ S 2 is a speech PSD and σ W 2 the noise PSD based on frames of said time to frequency transformation; d5) dividing the corresponding spectrum into a number N sb2 of sub-bands, each sub-band comprising a predetermined number n sb2 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·|{circumflex over (N)}| 2 , as the output for noise reduction of the input sound signal.