US 6,122,610 AGranted

Noise suppression for low bitrate speech coder

AssigneeVerance Corporation

InventorSteven H. Isabelle

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Abstract

Noise is suppressed in an input signal that carries a combination of noise and speech. The input signal is divided into signal blocks, which are processed to provide an estimate of a short-time perceptual band spectrum of the input signal. A determination is made at various points in time as to whether the input signal is carrying noise only or a combination of noise and speech. When the input signal is carrying noise only, the corresponding estimated short-time perceptual band spectrum of the input signal is used to update an estimate of an long term perceptual band spectrum of the noise. A noise suppression frequency response is then determined based on the estimate of the long term perceptual band spectrum of the noise and the short-time perceptual band spectrum of the input signal, and used to shape a current block of the input signal in accordance with the noise suppression frequency response.

Claims21

Dependent claims

A method for suppressing noise in an input signal that carries a combination of noise and speech, comprising the steps of:

dividing said input signal into signal blocks;
applying a Discrete Fourier Transform (DFT) to the signal blocks over a number of DFT bins to provide a complex-valued frequency domain representation of each block;
converting the frequency domain representations of the signal blocks to magnitude-only signals;
and
averaging the magnitude-only signals across different frequency bands to provide an estimate of a short-time perceptual band spectrum of the input signal;
wherein each of the different frequency bands is correlated with an associated plurality of the DFT bins;
determining, at various points in time, whether said input signal is carrying noise only, or a combination of noise and speech, and, when the input signal is carrying noise only, using the corresponding estimated short-time perceptual band spectrum of the input signal to update an estimate of a long term perceptual band spectrum of the noise;
determining a noise suppression frequency response based on said estimate of the long term perceptual band spectrum of the noise and the estimated short-time perceptual band spectrum of the input signal;
and
providing an all-pole time-domain filter in accordance with said noise suppression frequency response for time-domain shaping of a current block of the input signal to suppress noise therein.

7 more elements

An apparatus for suppressing noise in an input signal that carries a combination of noise and speech, comprising:

a signal preprocessor for dividing said input signal into signal blocks;
a Discrete Fourier transform (DFT) processor for processing said signal blocks over a number of DFT bins to provide a complex-valued frequency domain representation of each block;
means for computing a magnitude of said complex-valued frequency domain representation to provide a frequency domain magnitude spectrum;
an accumulator for accumulating said frequency domain magnitude spectrum into a perceptual-band spectrum comprising frequency bands of unequal width;
wherein values of the frequency domain magnitude spectrum are accumulated from different frequency bands, each of which is correlated with an associated plurality of the DFT bins;
a filter for filtering the perceptual-band spectrum to generate an estimate of a short-time perceptual-band spectrum comprising a current segment of the input signal;
a speech/pause detector for determining whether said input signal is currently noise only or a combination of speech and noise;
a noise spectrum estimator responsive to said speech/pause detector when the input signal is noise only for updating an estimate of a long term perceptual band spectrum of the noise based on the estimated short-time perceptual band spectrum of the input signal;
a spectral gain processor responsive to said noise spectrum estimator for determining a noise suppression frequency response;
and
a spectral shaping processor comprising an all-pole time-domain filter that is responsive to said spectral gain processor for time-domain shaping of a current block of the input signal to suppress noise therein.

8 more elements

Dependencies are inferred from the claim text.