US 6,311,154 B1 · Adaptive windows for analysis-by-synthesis CELP-type speech coding

Abstract

A speech coder and a method for speech coding wherein the speech signal is represented by an excitation signal applied to a synthesis filter. The speech is partitioned into frames and subframes. A classifier identifies which of several categories the speech frame belongs to, and a different coding method is applied to represent the excitation for each category. For some categories, one or more windows are identified for the frame where all or most of the excitation signal samples are assigned by a coding scheme. Performance is enhanced by coding the important segments of the excitation more accurately. The window locations are determined from a linear prediction residual by identifying peaks of the smoothed residual energy contour. The method adjusts the frame and subframe boundaries so that each window is located entirely within a modified subframe or frame. This eliminates the artificial restriction incurred when coding a frame or subframe in isolation, without regard for the local behavior of the speech signal across frame or subframe boundaries.

Claims38

Dependent claims

A method for coding a speech signal, comprising steps of:

partitioning samples of the speech signal into frames;
classifying the speech signal in each frame into one of a plurality of classes, wherein the step of classifying classifies a frame as being one of an unvoiced frame or a not unvoiced frame and classifies said not unvoiced frame as being one of a voiced frame or a transition frame;
determining the location of at least one window in the frame;
and
encoding an excitation for the frame, whereby all or substantially all of non-zero excitation amplitudes lie within the at least one window.

2 more elements

A wireless voice communicator, comprising;

a wireless transceiver comprising a transmitter and a receiver;
an input speech transducer and an output speech transducer;
and
a speech processor comprising,
a sampling and framing unit having an input coupled to an output of said input speech transducer for partitioning samples of an input speech signal into frames;
a first classifier for classifying a frame as being one of an unvoiced frame or a not unvoiced frame and a second classifier for classifying said not unvoiced frame as being one or a voiced frame or a transition frame;
a windowing unit for determining the location of at least one window in a frame;
and
an encoder for providing an encoded speech signal where, in an excitation for the frame, all or substantially all of non-zero excitation amplitudes lie within the at least one window;
said wireless communicator further comprising a modulator for modulating a carrier with the encoded speech signal, said modulator having an output coupled to an input of said transmitter;
a demodulator having an input coupled to an output of said receiver for demodulating a carrier that is encoded with a speech signal and that was transmitted from a remote transmitter;
and
said speech processor further comprising a decoder having an input coupled to an output of said demodulator for decoding an excitation from a frame wherein all or substantially all of non-zero excitation amolitudes lie within at least one window, said decoder having an output coupled to an input of said output speech transducer.

10 more elements

A speech decoder, comprising:

a class decoder having an input coupled to an input node of said speech decoder for extracting from an input bit stream predetermined ones of bits encoding class information for an encoded speech signal frame and for decoding the class information, wherein there are a plurality of predetermined classes;
said plurality of predetermined classes comprises a voiced class, an unvoiced class and a transition class;
and wherein said input bit stream is also coupled to an input of a LSP decoder;
a first multi-position switch element controlled by an output of said class decoder for directing said input bit stream to an input of one of selected one of a plurality of excitation generators, an individual one of said excitation generators corresponding to one of said plurality of predetermined classes;
a second multi-position switch element controlled by said output of said class decoder for coupling an output of the selected one of said excitation generators to an input of a synthesizer filter and, via a feedback path, also to said adaptive code book;
an unvoiced class excitation generator and a transition class excitation generator coupled between said first and second multi-position switch elements;
wherein for said transition class, at least one window position is decoded in a window decoder having an input coupled to said input bit stream;
and wherein a codebook vector is retrieved from a transition excitation fixed codebook using information concerning the at least one window location output from said window decoder and by multiplying a retrieved codebook vector;
and
wherein for said voiced class, the input bit stream encodes pitch information for the encoded speech signal frame which is decoded in a pitch decoder block having an output coupled to a window generator block that generates at least one window based on the decoded pitch information, said at least one window being used to retrieve, from an adaptive code book, an adaptive code book vector used for generating an excitation vector which is multiplied by a gain element and added to an adaptive codebook excitation to give a total excitation for a voiced frame.

7 more elements

Dependencies are inferred from the claim text.

Adaptive windows for analysis-by-synthesis CELP-type speech coding

Life of this patent

Adaptive windows for analysis-by-synthesis CELP-type speech coding

Life of this patent

Abstract

Claims38