US 5,890,108 A · Low bit-rate speech coding system and method using voicing probability determination

Abstract

A modular system and method is provided for low bit rate encoding and decoding of speech signals using voicing probability determination. The continuous input speech is divided into time segments of a predetermined length. For each segment the encoder of the system computes a model signal and subtracts the model signal from the original signal in the segment to obtain a residual excitation signal. Using the excitation signal the system computes the signal pitch and a parameter which is related to the relative content of voiced and unvoiced portions in the spectrum of the excitation signal, which is expressed as a ratio Pv, defined as a voicing probability. The voiced and the unvoiced portions of the excitation spectrum, as determined by the parameter Pv, are encoded using one or more parameters related to the energy of the excitation signal in a predetermined set of frequency bands. In the decoder, speech is synthesized from the transmitted parameters representing the model speech, the signal pitch, voicing probability and excitation levels in a reverse order. Boundary conditions between voiced and unvoiced segments are established to ensure amplitude and phase continuity for improved output speech quality. Perceptually smooth transition between frames is ensured by using an overlap and add method of synthesis. LPC interpolation and post-filtering is used to obtain output speech with improved perceptual quality.

Claims32

Dependent claims

A method for processing an audio signal comprising:

dividing the signal into segments, each segment representing one of a succession of time intervals;
computing for each segment a model of the signal in such segment;
subtracting the computed model from the original signal to obtain a residual excitation signal;
detecting for each segment the presence of a fundamental frequency F.sub.0 ;
determining for the excitation signal in each segment a ratio between voiced and unvoiced components of the signal in such segment on the basis of the fundamental frequency F.sub.0, said ratio being defined as a voicing probability Pv;
separating the excitation signal in each segment into a voiced portion and an unvoiced portion on the basis of the voicing probability Pv;
and
encoding parameters of the model of the signal in each segments and the voiced portion and the unvoiced portion of the excitation signal in each segment in separate data paths.

5 more elements

A system for processing an audio signal comprising:

means for dividing the signal into segments, each segment representing one of a succession of time intervals;
means for computing for each segment a model of the signal in such segment;
means for subtracting the computed model from the original signal to obtain a residual excitation signal;
means for detecting for each segment the presence of a fundamental frequency F.sub.0 ;
means for determining for the excitation signal in each segment a ratio between voiced and unvoiced components of the signal in such segment on the basis of the fundamental frequency F.sub.0, said ratio being defined as a voicing probability Pv;
means for separating the excitation signal in each segment into a voiced portion and an unvoiced portion on the basis of the voicing probability Pv;
and
means for encoding parameters of the model of the signal in each segments and the voiced portion and the unvoiced portion of the excitation signal in each segment in separate data paths.

5 more elements

Dependencies are inferred from the claim text.

Low bit-rate speech coding system and method using voicing probability determination

Life of this patent

Low bit-rate speech coding system and method using voicing probability determination

Life of this patent

Abstract

Claims32