Background noise reduction in sinusoidal based speech coding systems
AssigneeComsat Corporation
InventorSuat Yeldener
Life of this patent
Estimating the term…
Abstract
A method and apparatus to reduce background noise in speech signals in order to improve the quality and intelligibility of processed speech. In mobile communications environment, speech signals are degraded by additive random noise. A randomness of the noise, which is often described in terms of its first and second order statistics, make it difficult to remove much of the noise without introducing background artifacts. This is particularly true for lower signal to background noise ratios. The method and apparatus provides noise reduction without any knowledge of the signal to background noise ratio.
Claims16
A speech codec comprising:
- an input for receiving a speech signal;
- a linear time varying LPC filter that models the characteristics of the speech spectrum;
- a pitch detection section for generating an estimate of optimal pitch in the received speech;
- a voicing estimation section for computing the voicing probability that defines a cutoff frequency;
- spectral amplitude estimation section, responsive to the output of the pitch detection section and the voicing estimation section for generating an amplitude estimation for each harmonic;
- and
- a background noise generation section responsive to the output of said pitch detection section and voicing estimation section for modifying the amplitude estimation for each harmonic from said spectral amplitude estimation section.
A method of correcting for background noise in a speech codec comprising:
- detect voice activity for each frame of speech signal, based on the periodicity P0 and the auto-correlation function ACF of the speech signal;
- update the noise spectrum every speech segment where speech is not active, and estimate a long term noise spectrum;
- calculate a harmonic-by-harmonic noise-signal ratio and interpolate the harmonic spectral amplitudes;
- calculate long term average ACF and on the basis of an input of the detected voice activity provide an input to control the noise reduction gain, βm, from one frame to the next one;
- compute an attenuation factor for each harmonic based on the Estimated Noise to Signal Ratio (ENSR) for each harmonic lobe;
- calculate a noise attenuation factor for each harmonic;
- and
- apply the noise attenuation factor to scale the harmonic amplitudes that are computed during the encoding process.
Dependencies are inferred from the claim text.