Data processing: speech signal processing – linguistics – language – Speech signal processing – For storage or transmission
Reexamination Certificate
1998-03-23
2001-05-22
Zele, Krista (Department: 2748)
Data processing: speech signal processing, linguistics, language
Speech signal processing
For storage or transmission
C704S219000, C704S220000, C704S222000, C704S223000, C704S230000
Reexamination Certificate
active
06236961
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a speech signal coder for coding a speech signal of speech, music and so forth, and more particularly, to a signal coder capable of permitting high quality coding at low bit rate quantization.
Methods of efficiently coding a speech signal spectrum on a frequency axis are well known in the art as disclosed in, for instance, T. Moriya, “Transform coding of speech using a weighted vector quantizer” and N. Iwakami, “High-quality audio-coding at less than 64 kbit/s using transform-domain weighted interleave vector quantization (TWINVQ)”.
In these methods, DCT (Discrete Cosine Transform) coefficients of the speech signal are obtained by making an orthogonal transform thereof based on DCT for a number N of different points.
The DCT coefficient are then m divided at a number (M≦N) of points. The speech signal is then vector quantized by making a codebook retrieval for each of the M division points.
However, these prior art signal coders had the following problems in the speech signal coding.
Firstly, DCT coefficients of N points are all quantized uniformly. Therefore, reducing the bit number of a vector quantizer to reduce the bit rate, leads to the difficulty of obtaining satisfactory DCT coefficients which have a perceptually important role. In other words, although relatively satisfactory speech quality is obtainable by high bit rate coding, reducing the bit rate leads to extreme deterioration of the speech signal quality.
A second problem is posed by increasing the number M of points of the DCT coefficient division to improve the efficiency of vector quantization. Increasing the number M of points of the DCT coefficient division results in an increase of the dimension number of the vector quantizer. The dimension number exponentially increases the computational effort necessary for the vector quantization, and makes it impossible to reduce the bit rate.
SUMMARY OF THE INVENTION
The invention was made in view of the above problems, and an object of the invention is to provide a signal coder capable of coding of excellent speech quality at a low bit rate by quantizing speech signals having high frequency components with less computational effort.
According to the invention, there is provided a signal coder for coding speech signal comprising: parameter calculating means for calculating spectral and pitch parameters from speech signal and quantizing the calculated parameters; impulse response calculating means for calculating impulse responses of at least either of the quantized spectral or pitch parameters by using a filter constituted thereby; first orthogonal transfer means for obtaining a first transform signal by performing orthogonal transform of the speech signal or a signal derived therefrom using inverse filtering according to the quantized spectral and pitch parameters; second orthogonal transform means for obtaining a second transform of the predicted impulse response or a signal derived therefrom; and pulse quantizing means for quantizing the first transform signal either entirely or partly using the second transform signal.
The pulse quantizing means includes a first retrieval unit for performing determination of a first pulse group of a plurality of pulses recurrently according to the pitch parameters, and a second retrieval unit for making determination of a second pulse group according to the second transform signal, the signal coder further comprising a selector for selecting either the first or the second pulse group that represent the first transform signal.
The pulse quantizing means obtains the plurality of pulses by also using codevectors by retrieval of a codebook.
The pulse quantizer simultaneously quantizes the polarity or amplitude of at least one of the plurality of pulses.
According to another aspect of the present invention, there is provided a speech signal coder comprising: a first means for extracting a spectrum information and pitch information from a frame input speech signal; a second means for determining an impulse response signal of a filter defined by the spectrum information and pitch information; a third means for determining a response signal of a filter defined by the spectrum information and pitch information with an input signal; a fourth means for producing a difference signal between a perceptually weighted signal of the input speech signal and the response signal; a fifth means which receives the difference signal and has a filter defined by the spectrum information and pitch information; a sixth means for performing an orthogonal transform of the output of the fifth means and producing a first transform signal; a seventh means for performing an orthogonal transform of the impulse response signal and producing a second transform signal; an eighth means for determining a predetermined number of pulse positions on the basis of the first and second transform signals; a ninth means for determining a gain code vector using a gain codebook on the basis of the first and second transform signals, and determined pulse position data; a tenth means for determining an excitation signal on the basis of the gain code vector and determined pulse; an eleventh means for performing inverse-orthogonal transform of the excitation signal and producing as a first inverse-orthogonal; and a twelfth means for outputting a response signal based on the first inverse-orthogonal transform signal, spectrum information and pitch information as the input signal of the third means.
According to other aspect of the present invention, there is provided a speech signal coder comprising: a first means for extracting a spectrum information and pitch information from a frame input speech signal; a second means for determining an impulse response signal of a filter defined by the spectrum information and pitch information; a third means for determining a response signal of a filter defined by the spectrum information and pitch information with an input signal; a fourth means for producing a difference signal between a perceptually weighted signal of the input speech signal and the response signal; a fifth means which receives the difference signal and has a filter defined by the spectrum information and pitch information; a sixth means for performing an orthogonal transform of the output of the fifth means and producing a first transform signal; a seventh means for performing an orthogonal transform of the impulse response signal and producing a second transform signal; an eighth means for determining a predetermined number of pulse positions on the basis of the first and second transform signals and determining an amplitude codevector by using an amplitude codebook; a ninth means for determining a gain code vector using a gain codebook on the basis of the first and second transform signals, and determined pulse position data; a tenth means for determining an excitation signal on the basis of the gain code vector and determined pulse; an eleventh means for performing inverse-orthogonal transform of the excitation signal and producing as a first inverse-orthogonal signal; and a twelfth means for outputting a response signal based on the first inverse-orthogonal transform signal, spectrum information and pitch information as the input signal of the third means.
According to still another aspect of the present invention, there is provided a speech signal coder comprising: a first means for extracting a spectrum information and pitch information from a frame input speech signal; a second means for determining an impulse response signal of a filter defined by the spectrum information; a third means for determining a response signal of a filter defined by the spectrum information and pitch information with an input signal; a fourth means for producing a difference signal between a perceptually weighted signal of the input speech signal and the response signal; a fifth means which receives the difference signal and has a filter defined by the spectrum information and pitch information; a sixth means for performing an o
NEC Corporation
Ostrolenk Faber Gerb & Soffen, LLP
Sax Robert Louis
Zele Krista
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