Data processing: speech signal processing – linguistics – language – Speech signal processing – For storage or transmission
Reexamination Certificate
1998-04-02
2001-03-27
Dorvil, Richemond (Department: 2741)
Data processing: speech signal processing, linguistics, language
Speech signal processing
For storage or transmission
C704S204000, C704S219000
Reexamination Certificate
active
06208962
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a signal coding system. More specifically, the invention relates to a signal coding system for coding a voice signal or musical signal at low bit rate and in high quality.
2. Description of the Related Art
Systems for coding a voice signal or a musical signal at high efficiency on a frequency axis have been proposed in T. Moriya et al. “Transform Coding of Speech Using Weighted Vector Quantizer”, IEEE Journal on Selected Areas in Communications, Vol. JSAC-6, pp 425 to 431, 1988 or N. Iwakami et al., “High-Quality Audio-Coding at Less Than 64 kbit/Using Transform-Domain Weighted Interleave Vector Quantization (TWINVQ)”, Proc. ICASSP-95, pp 3095 to 3098, 1995, for example.
In the method disclosed in any of the foregoing publications, an orthogonal transformation of a voice or musical signals is performed using DCT (Discrete Cosine Transform) of a point N. Then, a DCT coefficient is divided per predetermined number of points M (M·N) for vector quantization per M point using a code book.
By the methods disclosed in the foregoing publications, the following drawbacks are encountered.
At first, when a bit rate is relatively high, relatively high sound quality can be provided. However, when the bit rate is lower, the sound quality becomes lower. The primary cause is that harmonics component of DCT coefficient cannot be expressed in vector quantization in lesser number of quantization bits.
Next, when a dividing point number M is set to be large in order to enhance performance of vector quantization, the number of bits of a vector quantizer increases exponentially for the amount required for vector quantization.
SUMMARY OF THE INVENTION
The present invention has been worked out for solving the drawbacks in the prior art as set froth above. Therefore, it is an object of the present invention to provide a signal coding system which can suppress degradation of acousticity with relatively small arithmetic amount even when a bit rate is low.
A signal coding system, according to the present invention, comprises:
predicting means for deriving a predictive residual error depending upon a result of prediction of an input signal;
orthogonal transforming means for deriving an orthogonal transformation coefficient by orthogonal transformation of said predictive residual error;
coefficient calculating means for expressing an envelop of said orthogonal transformation coefficient with a coefficient of a predetermined degree; and quantizing means for quantizing by expressing the orthogonal transformation coefficient by combination of a plurality of pulse trains depending upon said coefficient thus expressed, for outputting a result of quantization by deriving a spectral parameter from said input signal, the coefficient expressed by said coefficient calculating means and quantization result of said quantizing means in combination.
In the signal coding system according to the present invention, the input signal is predicted and the predicted residual error signal is effected by an orthogonal transformation. Then, a coefficient of smaller degree for expressing the envelop of the orthogonal transformation coefficient, is calculated. Quantization is performed by expressing the orthogonal transformation coefficient with a combination of a plurality of pulse trains with determining the position to generate the pulse. It is also possible to calculate the fine structure of the orthogonal transformation coefficient instead of calculating the coefficient of the envelop of the orthogonal transformation coefficient, or to calculate the fine structure of the orthogonal transformation coefficient in conjunction with calculating the coefficient of the envelop of the orthogonal transformation coefficient. Since the orthogonal transformation coefficient is expressed by a combination of a plurality of pulse trains it is possible to perform coding more efficiently than that of the prior art.
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Dorvil Richemond
NEC Corporation
Ostrolenk Faber Gerb & Soffen, LLP
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