Method of and device for quantizing spectral parameters in digital speech coders
First Claim
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1. A method of speech signal digital coding which comprises the steps of:
- converting a speech signal into a sequence of digital samples divided into frames of a preset number of samples; and
submitting said digital samples to a spectral analysis for generating at least a group of spectral parameters which are quantized and transformed into a first set of indexes (j1), wherein at each frame, during a coding phase, speech periods with a high correlation are recognized starting from the indexes of the first set and, for these periods, said first set of indexes (j1) is converted into a second set of indexes (j4) coded with a number of bits lower than that necessary for coding the first set, and the second set of indexes (j4) is inserted into the coded signal, together with a signalling indicating that conversion has taken place, while for other periods the first set of indexes is inserted into the coded signal.
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Abstract
A method of and a device for speech signal digital coding are described, where spectral parameters are quantized at each frame in order to exploit the actual correlation inside a frame or between contiguous frames. The quantization devices (DQ) recognize strongly correlated signal periods by using a first set of indexes (j1), representing the parameters and provided by the spectral analysis circuits (ABT, ALT), and in these periods they convert the same indexes into a second set of indexes (j4) which can be coded with a lower number of bits and which is inserted into the coded signal in place of the first set.
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11 Claims
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1. A method of speech signal digital coding which comprises the steps of:
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converting a speech signal into a sequence of digital samples divided into frames of a preset number of samples; and submitting said digital samples to a spectral analysis for generating at least a group of spectral parameters which are quantized and transformed into a first set of indexes (j1), wherein at each frame, during a coding phase, speech periods with a high correlation are recognized starting from the indexes of the first set and, for these periods, said first set of indexes (j1) is converted into a second set of indexes (j4) coded with a number of bits lower than that necessary for coding the first set, and the second set of indexes (j4) is inserted into the coded signal, together with a signalling indicating that conversion has taken place, while for other periods the first set of indexes is inserted into the coded signal. - View Dependent Claims (2, 3, 4, 5)
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6. A device for speech signal digital coding, comprising means (AN, TR) for converting a speech signal into a sequence of digital samples and for dividing the sequence into frames comprising a preset number of samples, means (ABT, ALT) for spectral analysis of samples in said frames and quantization of parameters obtained as a result of spectral analysis, the means for the spectral analysis generating at each frame at least a first set of indexes (j1) representing a value of the parameters in that frame, and means (CV) for generating a coded signal containing information relevant to said parameters, said device comprising, on a coding side:
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means (DQ) for;
recognizing, starting from the indexes (j1) of said first set, frames in which the speech signal presents a high correlation;
converting, for presenting a high correlation frame, the first set of indexes (j1) into a second set of indexes (j4), coded with a number of bits lower than that necessary for coding the indexes of the first set; and
generating and transmitting to a decoder a signalling indicating that conversion has taken place; andmeans (MX) for supplying, in the frames presenting a high correlation, the means for generating (CV) with the second set of indexes in place of the first set of indexes. - View Dependent Claims (7, 8, 9, 10, 11)
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Specification