Fujitsu Corporation

Yasuji Ohta

Tomohiko Taniguchi

Yoshinori Tanaka

Fumio Amano

Shigeyuki Unagami

Hideaki Kurihara

Akira Sasama

Yoshihiro Sakai

Koji Okazaki

Mark A Johnson

Kohei Iseda

Shigeyuki Unnagami

Sigeyuki Unagami

Mark Johnson

Mark Allan Johnson

A larger number, L', of delta vectors .DELTA..sub.i (i=0, 1, 2, . . . , L'-1) than the required number L are each multiplied by a matrix of a linear predictive synthesis filter (3), their power (A.DELTA..sub.i).sup.T (A.DELTA..sub.i) is evaluated (42), and the delta vectors are reordered in decreasing order of power (43); then, L delta vectors are selected in decreasing order of power, the largest power first, to construct a tree-structure data code book (41), using which A-b-S vector quantization is performed (48). This provides increased freedom for the space formed by the delta vectors and improves quantization characteristics. Further, variable rate encoding is achieved by taking advantage of the structure of the tree-structure data code book.

Speech encoding method and apparatus using tree-structure delta code book

Speech coding uses a periodic excitation signal source, a non-periodic signal excitation source, a synthesizing unit, a filter, and an error evaluating unit. The synthesizing unit synthesizes a periodic excitation signal and a non-periodic excitation signal output from the above-mentioned sources to generate an excitation sound source signal. The filter regenerates an input speech signal from the excitation sound signal. The error evaluating unit controls the periodic excitation signal source and the non-periodic excitation signal source so that the above-mentioned units output periodic and non-periodic excitation signals which minimize a difference of the regenerated signal from an input speech signal. When the error is minimized, the above-mentioned sound source is supplied to a feedback excitation signal modifying unit. The feedback excitation modifying unit reduces a non-periodic component in the above-mentioned supplied signal so that the non-periodic component is reduced more when the relative amount of the periodic component is greater. The modified signal is fed back to the periodic excitation signal source unit to modify the content thereof.

Speech signal coding system wherein non-periodic component feedback to

Speech coding system having codebook storing differential vectors

A gain-shape vector quantization apparatus is provided for encoding and decoding, to transmit and receive compressed speech signals. A selected plurality of vectors are read from a code book based upon an index signal. The vectors are added in an adder and synthesis filtered by a synthesis filter, in either order, to produce an output. This output is subtracted from an input speech signal to produce an error signal. An evaluation unit produces an index to select the plurality of vectors read from the code book memory based on the error signal in order to minimize this error signal. The evaluation unit produces gain adjusting signals which can be used to adjust gains of the vectors read from the code book. In an encoder, signals indicative of the gain adjusting signal and the index signal are transmitted by a transmitter of the encoder to send a quantized speech signal to a receiver of a decoder. In the decoder, after the signals indicative of the gain adjusting signal and the index are received by the receiver of the decoder, an index and gain adjusting signal is derived for use to control reading of vectors from a code book and gains thereon to reproduce the speech signal.

Gain-shape vector quantization method and apparatus

A code excited linear prediction (CELP) type speech signal coding system is provided, a code vector obtained by applying linear prediction to a vector of a residual speech signal of white noise is stored in a code book. A pitch prediction vector obtained by applying linear prediction to a residual signal of a preceding frame is given a delay corresponding to a pitch frequency and added to the code vector. Use is made of an impulse vector obtained by applying linear prediction to a residual signal vector of impulses having a predetermined relationship with the vectors of the white noise code book. Variable gains are given to at least the above code vector and impulse vector, a reproduced signal is produced, and this reproduced signal is used for identification of the input speech signal. Thus, a pulse series corresponding to the sound source of voiced speech sounds is created.

Code excited linear prediction speech coding system

Pitch periods for a long term predictor included in a speech codec are searched in two searching stages. In the first searching stage, probable pitch periods are searched skipping a constant number of pitch periods, and in the second searching stage, pitch periods including the pitch period determined in the first searching stage and pitch periods neighboring the pitch period on both sides are searched.

Pitch period searching method and circuit for speech codec

A speech coding apparatus coupled to a transmission channel includes m (m is an integer greater than 1) coders, m decoders and m or (m-1) error correcting coders. The apparatus also includes an evaluation unit which evaluates a quality of each of reproduced speech signals from the input speech signal and the reproduced speech signals and which outputs an evaluated quality of each of the reproduced speech signals. The quality of each of the reproduced speech signals is evaluated in a state having no transmission error. A decision unit identifies one of the m coders which provides the reproduced speech signal having a smallest distortion on the basis of the evaluated quality of each of the reproduced speech signals, a current error rate of the transmission channel and error correcting abilities of the error correcting coders, and generates a coder identification number representative of a selected one of the m coders. An output part outputs a multiplexed transmission signal including the coded speech signal generated by the one of the m coders identified by the decision unit and the error correcting code generated by a corresponding one of the m error correcting coders.

Speech coding apparatus using multimode coding

A CELP type speech coding system is provided with an arithmetic processing unit which transforms a perceptual weighted input speech signal vector AX to a vector .sup.t AAX, a sparse adaptive codebook which stores a plurality of pitch prediction residual vectors P sparsed by a sparse unit, and a multiplying unit which multiplies the successively read out vectors P and the output .sup.t AAX from the arithmetic processing unit. In addition, the CELP type speech coding system includes a filter operation unit which performs a filter operation on the vectors P, and an evaluation unit which finds the optimum vector P based on the output from the filter operation unit, so as to enable reduction of the amount of arithmetic operations.

Speech coding and decoding system

An apparatus for compressing and decompressing speech signals. The encoder or decoder comprises a plurality of codebooks each controlling a plurality of indexed code vectors for a different frequency band. Each of the codebooks is provided with a synthesis filter for reproducing a signal wave shape based on a code vector provided by the corresponding codebook. The encoder or decoder further comprises an adder for computing a sum of signal wave shapes reproduced by the synthesis filters. This arrangement can reduce the memory size of each codebook used for an encoding or a decoding process and an amount of operations of the encoding or decoding process.

Vector quantization encoder and vector quantization decoder

Speech encoding/decoding apparatus having selected encoders

A gain-shape vector quantization apparatus for compressing the data of voice signal. A code book portion is constituted by a plurality of shape vectors which produce a plurality of selected shape vectors. A plurality of variable gain circuits impart gains to each shape vector produced from the code book portion. A plurality of synthesis filters regenerate signals from the outputs of the variable gain circuits. An adder adds the signals regenerated by the synthesis filters. An evaluation unit produces an index to select a plurality of shape vectors in the code book portion in order to minimize an error between the output of the adder and an input speech signal and further produces gain adjusting signal for the variable gain circuits.

Gain-shape vector quantization apparatus

A voice coding apparatus includes a pitch detecting circuit which detects a pitch period of a voice signal; a pitch waveform generating circuit which samples the voice signal for a plurality of pitches based on the pitch period detected by the pitch detecting circuit and which generates a waveform of one pitch from the waveform of the plurality of pitches; a band restriction circuit which restricts the frequency band of the one pitch waveform generated in the pitch waveform generating circuit; and a coding circuit for coding the voice waveform which is band restricted in the band restriction circuit. The sampling number of the waveform for a plurality of pitches and the restricted bandwidth can be changed in accordance with the amount of the pitch period extracted in the pitch detecting circuit. Further, the pitch detecting circuit is able to correctly detect the pitch period even when the pitch period is not a multiple of the sampling period.

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Kawasaki, Japan

Yasuji Ohta