EP0280827A1
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EP
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Pitch detection process and speech coder using said process
Assignee: International Business Machines Corp
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Filing: 1987-03-05
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Granted: —
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Expires: 2007-03-05
Abstract
Abstract A pitch data detecting means to be used to adjust long term predictive means in a pulse excitation speech coder. A residual signal r(n) is first derived from the speech signal s(n) through short term filtering then r(n) is processed to provide a prediction error signal e(n) to be pulse excitation encoded. The generation of e(n) involves predicting a residual through Long Term Prediction operations including measuring a pitch related factor M, through a dual steps process with first step providing a coarse M value through peak clipping and sign transition detection, and then second step for adjusting said M to a finer value through autocorrelations operating about the roughly spaced peaks.
Inventors
- 👤 Claude Galand
- 👤 Michèle Rosso
- 👤 Thierry Liethoudt
- 👤 Philippe Elie
- 👤 Emmanuel Lancon
- 👤 Hubert Crepy
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-03 21:07
CPC Classifications
G; G10; G10L; G10L19/00; G10L19/04; G10L19/08; G10L25/00; G10L25/90
Claims Analysis
Total Claims: 10
Claim 1
Independent Claim
179 words
A digital process for detecting a pitch related data (M) in a sampled speech representative signal split into consecutive fixed length, blocks of samples said process including a rough M determination followed by a fine M determination, respectively including: (a) for the rough M determination: - setting signal dependent positive threshold (Th⁺) and negative threshold (Th⁻); - locating and storing samples representative of the signal block, having magnitudes above and below said Th⁺ and Th⁻ respectively; - locating significant sign transitions within said stored samples; - computing the number Mʹ of stored samples between the consecutively located significant transitions; and computing a rough M value as the mean value of Mʹ for the considered block; and, (b) for the fine M determination: - setting autocorrelation zones about the multiples of M spaced peak samples; - splitting the considered block of signal samples into consecutive sub-blocks; -auto correlating a current sub-block of samples with sub-blocks of samples the first of which is one sample of an auto-correlation zone; and - locating the auto-correlation peak to determine the fine M value.
Claim 2
Dependent Claim
179 words
A digital process for detecting a pitch related data (M) in a sampled speech representative signal split into consecutive fixed length, blocks of samples said process including a rough M determination followed by a fine M determination, respectively including: (a) for the rough M determination: - setting signal dependent positive threshold (Th⁺) and negative threshold (Th⁻); - locating and storing samples representative of the signal block, having magnitudes above and below said Th⁺ and Th⁻ respectively; - locating significant sign transitions within said stored samples; - computing the number Mʹ of stored samples between the consecutively located significant transitions; and computing a rough M value as the mean value of Mʹ for the considered block; and, (b) for the fine M determination: - setting autocorrelation zones about the multiples of M spaced peak samples; - splitting the considered block of signal samples into consecutive sub-blocks; -auto correlating a current sub-block of samples with sub-blocks of samples the first of which is one sample of an auto-correlation zone; and - locating the auto-correlation peak to determine the fine M value.
Claim 3
Dependent Claim
72 words
A process according to claim 1 wherein said setting autocorrelation zones include: - locating autocorrelation zones based on roughly located pitched peaks and a predetermined Delta variation, said zones including the samples whose index kʹ = K.M± Delta, K being an integer value 1, 2, 3; and, - eliminating from these located zones, non significant kʹ index valued ones, i.e. keeping only 40 ≦kʹ≦ 120 wherein 40 samples represents a sub-block length.
Claim 4
Dependent Claim
23 words
A process according to claim 1 or 2 wherein said autocorrelation operations are operated over reconstructed shifted samples of said speech representative signal.
Claim 5
Dependent Claim
47 words
A digital process according to claim 1, 2 or 3 wherein said sampled speech representative signal is a so called residual signal r(n) derived from said signal through a short term-filtering operation using a digital filter the a(i) coefficients of which are derived from the speech signal.
Claim 6
Dependent Claim
44 words
A digital process according to claim 4 wherein said determined M value is used to adjust a Long Term Prediction (LTP) filter used to generate a predicted residual signal to be subtracted from the current residual signal and derive therefrom a prediction error signal.
Claim 7
Dependent Claim
43 words
A digital process according to claim 5 wherein said prediction error signal e(n) is in turn encoded using Regular Pulse Excitation techniques converting each sub-block of e(n) samples into a shorter sequence selected among a set of sequences of relatively fixed positions samples.
Claim 8
Dependent Claim
46 words
A digital process according to anyone of claims 5 through 4 wherein said M value is used to adjust said LTP filter with a gain factor b according to wherein N is a predetermined integer function of the number of samples within a block of samples.
Claim 9
Dependent Claim
204 words
A digital speech coder for coding a speech signal s(n), including: - short term adaptive filtering means (10) filtering said s(n) signal and providing a residual signal r(n); - a subtracting device having a (+) input and a (-) input said (+) input being connected to be fed with said r(n) signal, and said subtracting device providing a prediction error signal e(n); - a regular pulse excitation (RPE) coder for converting fixed length sub-blocks of e(n) samples into shorter (RPE) sequences of samples; - quantizing means for quantizing said RPE, sequences; - decoding means for decoding the quantized output; - adding means connected to said decoding means; - Long Term Predictive (LTP) coding means including delay means connected to said adding means, for delaying the adder output by a delay equal to M and multiply said delayed output by a gain b, whereby a predicted residual signal x(n) is generated; - LTP coefficient computing means sensitive to said r(n) signal and connected to said delay means for deriving said M according to the process of claim 1, and b gain according to claim 5; and - means for applying said predicted residual to both the subtracting (-) input and the second adding means input.
Claim 10
Dependent Claim
127 words
A digital speech coder according to claim 8 wherein said LTP coding means include: - a one block length shift register having an input connected to the adding means output, an adjustable tap, and an output; - a multiplier connected to said tap and having an output connected to both (-) subtractor input and to second adder input; - LTP coefficients computing means connected to said shift register output and sensitive to the residual r(n) signal to generate a pitch related M data according to claim 1 or 2 and a gain factor b according to claim 5; - means for shifting said tap to be spaced from the shift register input by a delay M; and, - means for applying said b gain to said multiplier.
References Cited (Backward Citations)
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