Speech coding system having codebook storing differential vector

Details Speech coding system having codebook storing differential vector Speech coding system having codebook storing differential vector

1992-05-14

1994-06-21

Fleming, Michael R.

395 229, G10L 900

Patent

active

053234863

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a speech coding system for compression of data of speech signals, and more particularly relates to a speech coding system using analysis-by-synthesis (A-b-S) type vector quantization for coding at a transmission speed of 4 to 16 kbps, that is, using vector quantization performing analysis by synthesis.
2. Background of the Related Art
Speech coders using A-b-S type vector quantization, for example, code-excited linear prediction (CELP) coders, have in recent years been considered promising as speech coders for compression of speech signals while maintaining quality in intracompany systems, digital mobile radio communication, etc. In such a quantized speech coder (hereinafter simply referred to as a "coder"), predictive weighting is applied to the code vectors of a codebook to produce reproduced signals, the error powers between the reproduced signals and the input speech signal are evaluated, and the number (index) of the code vector giving the smallest error is decided on or determined and sent to the receiver side.
A coder using the above-mentioned A-b-S type vector quantization system performs processing so as to apply linear prediction analysis filter processing to each of the vectors of the sound generator signals, of which there are about 1000 patterns stored in the codebook, and retrieve from among the approximately 1000 patterns the one pattern giving the smallest error between the reproduced speech signals and the input speech signal to be coded.
Due to the need for instantaneousness in conversation, the above-mentioned retrieval processing must be performed in real time. This being so, the retrieval processing must be performed continuously during the conversation at short time intervals of 5 ms, for example.
As mentioned later, however, the retrieval processing includes complicated computation operations of filter computation and correlation computation. The amount of computation required for these computation operations is huge, being, for example, several 100M multiplications and additions per second. To deal with this computational complexity, even with digital signal processors (DSP), which are the highest in speed at present, several DSP chips are required. In the case of use for cellular telephones, for example, there is the problem of achieving a small size and a low power consumption.


SUMMARY OF THE INVENTION

The present invention, in consideration of the above-mentioned problems, has as its object the provision of a speech coding system which can tremendously reduce the amount of computation while maintaining the properties of an A-b-S type vector quantization coder of high quality and high efficiency.
The present invention, to achieve the above object, adds differential vectors (hereinafter referred to as delta vectors) .DELTA.C.sub.n to the previous code vectors C.sub.n-1 among the code vectors of the codebook and stores in the codebook the group of code vectors producing the next code vectors C.sub.n. Here, n indicates the order in the group of code vectors.


BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be explained below while referring to the appended drawings, in which:
FIG. 1 is a view for explaining the mechanism of speech generation,
FIG. 2 is a block diagram showing the general construction of an A-b-S type vector quantization speech coder,
FIG. 3 is a block diagram showing in more detail the portion of the codebook retrieval processing in the construction of FIG. 2,
FIG. 4 is a view showing the basic concept of the present invention,
FIG. 5 is a view showing simply the concept of the first embodiment based on the present invention,
FIG. 6 is a block diagram showing in more detail the portion of the codebook retrieval processing based on the first embodiment,
FIG. 7 is a block diagram showing in more detail the portion of the codebook retrieval processing based on the first embodiment using another example,
FIG. 8 is a view showing another example of the auto correlatio

REFERENCES:
patent: 4868867 (1989-09-01), Davidson et al.
patent: 4991214 (1991-02-01), Freeman et al.
patent: 5144671 (1992-09-01), Mazor et al.
patent: 5151968 (1992-09-01), Tanaka et al.
Ozawa et al. "4kb/s Improved Celp Coder with Efficient Vector Quantization" IEEE, 1991, pp. 213-216.

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