Electrical audio signal processing systems and devices – One-way audio signal program distribution – Public address system
Patent
1990-02-08
1992-05-19
Kemeny, Emanuel S.
Electrical audio signal processing systems and devices
One-way audio signal program distribution
Public address system
381 34, G01L 500
Patent
active
051154692
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a speech encoding and decoding apparatus for transmitting a speech signal after information compression processing has been applied.
Recently, a speech encoding and decoding apparatus for compressing speech information to data of about 4 to 16 kbps at a high efficiency has been demanded for in-house communication systems, digital mobile radio systems and speech storing systems.
2. Description of Related Art
As the first prior art structure of a speech prediction encoding apparatus, there is provided an adaptive prediction encoding apparatus for multiplexing the prediction parameters (vocal tract information) of a predictor and residual signal (excitation information) for transmission to the receiving station.
FIG. 1 is a block diagram of an encoder used in the speech encoding apparatus of the first prior art structure. Encoder 100, comprises linear prediction analysis unit 101, predictor 102, quantizer 103, multiplexing unit 104 and adders 105 and 106.
Linear prediction analysis unit 101 analyzes input speech signals and outputs prediction parameters, and predictor 102 predicts input signals using an output from adder 106 (described below) and prediction parameters from linear prediction analysis unit 101. Adder 105 outputs error data by computing the difference between an input speech signal and the predicted signal, quantizer 103 obtains a residual signal by quantizing the error data, and adder 106 adds the output from predictor 102 to that of quantizer 103, thereby enabling the output to be fed back to predictor 102. Multiplexing unit 104 multiplexes prediction parameters from linear prediction analysis unit 101 and a residual signal from quantizer 103 for transmission to a receiving station.
With such a structure, linear prediction analysis unit 101 performs a linear prediction analysis of an input signal at every predetermined frame period, thereby extracting prediction parameters as vocal tract information to which appropriate bits are assigned by an encoder (not shown). The prediction parameters are thus encoded and output to predictor 102 and multiplexing unit 104. Predictor 102 predicts an input signal based on the prediction parameters and an output from adder 106. Adder 105 computes the error data (the difference between the predicted information and the input signal), and quantizer 103 quantizes the error data, thereby assigning appropriate bits to the error data to provide a residual signal. This residual signal is output to multiplexing unit 104 as excitation information.
After that, the encoded prediction parameter and residual signal are multiplexed by multiplexing unit 104 and transmitted to a receiving station.
Adder 106 adds an input signal predicted by predictor 102 and a residual signal quantized by quantizer 103. An addition output is again input to predictor 102 and is used to predict the input signal together with the prediction parameters.
In this case, the number of bits assigned to prediction parameters for each frame is fixed at .alpha.-bits per frame and the number of bits assigned to the residual signal is fixed at .beta.-bits per frame. Therefore, the (.alpha.+.beta.) bits for each frame are transmitted to the receiving station. In this case, the transmission rate is, for example, 8 kbps.
FIG. 2 is a block diagram showing a second prior art structure of the speech encoding apparatus. This prior art structure is a Code Excited Linear Prediction (CELP) encoder which is known as a low bit rate speech encoder.
Principally, a CELP encoder, like the first prior art structure shown in FIG. 1, is an apparatus for encoding and transmitting linear prediction code parameters (LPC or prediction parameters) obtained from an LPC analysis and a residual signal. However, this CELP encoder represents a residual signal by using one of the residual patterns within a code book, thereby obtaining high efficiency encoding.
Details of CELP are disclosed in Atal, B. S., and Schroeder, M. R. "Stochastic Coding of
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Amano Fumio
Iseda Kohei
Ohta Yasuji
Okazaki Koji
Tanaka Yoshinori
Doerrler Michelle
Fujitsu Limited
Kemeny Emanuel S.
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