EP0628946A1
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EP
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Method of and device for quantizing spectral parameters in digital speech coders
Assignee: TIM SpA
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Filing: 1994-06-09
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Granted: —
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Expires: 2014-06-09
Abstract
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.
Inventors
- 👤 Daniele Sereno
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-05 10:58
CPC Classifications
G; G10; G10L; G10L19/00; G10L19/04; G10L19/06
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
156 words
A method of speech signal digital coding, in which the signal is converted into a sequence of digital samples divided into frames of a preset number of samples and is submitted 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), characterized in that at each frame, during the 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 (j₄) which can be 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 the other periods the first set of indexes is inserted into the coded signal.
Claim 2
Dependent Claim
107 words
A method according to claim 1, characterized in that the differences are computed between the indexes (j₁) of the first set generated for the current frame and those generated at the previous frame; the absolute values of said differences are compared with a threshold; a flag (C) is generated constituting said signalling and having a preset logic value, which indicates high correlation periods, when all absolute values lie in an interval of values limited by the threshold; and, for periods with a high correlation, these differences are divided into groups and vector quantization of the individual groups is carried out, generating the second set of indexes (j₄).
Claim 3
Dependent Claim
25 words
A method according to claim 1 or 2, characterized in that said spectral parameters are at least the representative parameters of speech signal short-term correlation.
Claim 4
Independent Claim
37 words
A method according to any of the preceding claims, characterized in that the indexes (j₄) of the second set are directly computed at each frame, starting from the difference values in each group, without storing quantization tables.
Claim 5
Dependent Claim
117 words
A method according to claim 2 or claims 3 or 4 if referred to claim 2, comprising a decoding phase in which said spectral parameters are reconstructed and the reconstructed parameters are supplied to units synthesizing a decoded signal, characterized in that the spectral parameters are directly reconstructed starting from the coded signal received if said flag (C) has a logic value complementary to the preset value and, if flag (C) has the preset logic value, the received signal is submitted to an inverse quantization for reconstructing the differences between indexes representative of the parameters relevant to the current frame and to the previous frame, and the first set of indexes is reconstructed starting from these differences.
Claim 6
Independent Claim
213 words
A device for speech signal digital coding, comprising means (AN, TR) for converting the 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 the spectral analysis of speech signal to be coded and the quantization of the parameters obtained as the result of the analysis, which means generate at each frame at least a first set of indexes (j₁) representing the value of the parameters in that frame, and means (CV) for generating a coded signal containing information relevant to said parameters, characterized in that it comprises, on the coding side: - means (DQ) for: recognizing, starting from the indexes (j₁) of the said first set, frames in which the speech signal presents a high correlation; converting, for these frames, the first set of indexes (j₁) into a second set of indexes (j₄), which can be 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; and - means (MX) for supplying, in these frames, the means (CV) generating the coded signal with the second set of indexes in place of the first one.
Claim 7
Dependent Claim
166 words
A device according to claim 6, characterized in that the means (DQ) for recognizing frames with a high correlation comprise: - means (S0...S8) for computing the values of the differences between each index of the first set (j₁) and the value assumed by the same index at the previous frame; - means (CS0...CS8) for comparing the absolute value of each difference with a threshold and generating signals the logic value of which indicates whether the absolute value has exceeded the threshold or not; - means (AN) receiving the signals generated by the comparison means and emitting a flag which has a preset logic value when all output signals of the comparison means have the same logic value indicating that the threshold has not been exceeded, said flag being inserted into the coded signal and making up said signalling; - means (QV0...QV2), enabled by said flag when it has the preset logic value, for vector quantization of groups of differences, generating the aforesaid second set of indexes.
Claim 8
Dependent Claim
41 words
A device according to claim 7, characterized in that the vector quantization means (QV0...QV2) are made up of a single computing unit which directly computes the index representing the individual difference groups starting from the input values, without storing quantization tables.
Claim 9
Independent Claim
90 words
A device according to any of the claims from 6 to 8, characterized in that it comprises, on the decoding side, means (DM), controlled by said flag, which supply the coded information relevant to said parameters either to units (DJ4, RT, SD) for reconstructing the first set of indexes (j₁) and supplying the reconstructed set to units (DJ1) for parameter reconstruction, if said flag presents the preset logic value, or directly to the units (DJ1) for parameter reconstruction, if the flag presents the logic value complementary to the preset one.
Claim 10
Dependent Claim
77 words
A device according to claim 9, characterized in that the units (DJ4, RT, SD) reconstructing the first set of indexes comprise means (DJ4) for reconstructing the differences between the indexes of the first set relevant to a current frame and to a previous frame, and means (SD, RT) for storing said indexes relevant to a previous frame and adding them to the reconstructed differences, for reconstructing the indexes of the first set relevant to the current frame.
Claim 11
Independent Claim
28 words
A device according to any of claims from 6 to 10, characterized in that the spectral analysis means are means for short-term analysis of a linear prediction coder.
References Cited (Backward Citations)
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