32 7. References

A method is presented in this report to estimate the noise spectrum of speech utterances which are disturbed by additive noise. One advantage is that no speech pause detection is required. The processing is based on a calculation of the distribution density function of spectral magnitude values in a subband. The histogram for one subband is calculated for a past segment with a defined duration. Good results were obtained for a segment of 0,5 s. In this case the noise spectrum can also follow a slowly changing noise. Two applications of this technique are described in this report. The first one is an estimation of the actual SNR of a speech segment. Good results were obtained for a wide range of SNRs and for different noise signals. The second one is the use for an enhancement of noisy speech. The enhancement techniques attempted were a new form of spectral subtraction, and a modified high-pass filtering of the spectral envelopes in sub-bands.