Speech signal decoding method and apparatus, speech signal encoding/decoding method and apparatus, and program product therefor
First Claim
1. A speech signal decoding method for decoding information concerning at least a sound source signal, gain and linear prediction coefficients from a received signal, generating an excitation signal and linear prediction coefficients from decoded information, and driving a filter, which is constituted by the linear prediction coefficients, by the excitation signal to thereby decode a speech signal, comprising:
- smoothing the gain using a past value of the gain;
limiting the value of the smoothed gain based upon an amount of fluctuation calculated from the gain and the smoothed gain; and
decoding the speech signal using the gain that has been smoothed and limited.
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Abstract
The quality of reconstructed speech on which background noise is superimposed is improved in a speech signal decoding apparatus for generating a speech signal by driving a filter, which is constituted by linear prediction coefficients, by an excitation signal. A smoothing circuit smoothes sound source gain in a noise segment using sound source gain that was obtained in the past. A smoothing-quantity limiting circuit calculates an amount of fluctuation represented by dividing, by the sound source gain, the absolute value of the difference between the sound source gain and the sound source gain that has been smoothed, and limits the value of the smoothed gain in such a manner that the amount of fluctuation will not exceed a certain threshold value.
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Citations
48 Claims
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1. A speech signal decoding method for decoding information concerning at least a sound source signal, gain and linear prediction coefficients from a received signal, generating an excitation signal and linear prediction coefficients from decoded information, and driving a filter, which is constituted by the linear prediction coefficients, by the excitation signal to thereby decode a speech signal, comprising:
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smoothing the gain using a past value of the gain;
limiting the value of the smoothed gain based upon an amount of fluctuation calculated from the gain and the smoothed gain; and
decoding the speech signal using the gain that has been smoothed and limited. - View Dependent Claims (2, 3, 4, 5)
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6. A speech signal decoding method for decoding information concerning an excitation signal and linear prediction coefficients from a received signal, generating an excitation signal and linear prediction coefficients from the decoded information, and driving a filter, which is constituted by the linear prediction coefficients, by the excitation signal to thereby decode a speech signal, comprising:
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deriving a norm of the excitation signal at regular intervals;
smoothing the norm using a past value of the norm;
limiting the value of the smoothed norm based upon an amount of fluctuation calculated from the norm and the smoothed norm;
changing the amplitude of the excitation signal in said intervals using said norm and the norm that has been smoothed and limited; and
driving the filter by the excitation signal the amplitude of which has been changed. - View Dependent Claims (7, 8, 9, 10, 11)
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12. A speech signal decoding method for decoding information concerning an excitation signal and linear prediction coefficients from a received signal, generating the excitation signal and the linear prediction coefficients from the decoded information, and driving a filter, which is constituted by the linear prediction coefficients, by the excitation signal to thereby decode a speech signal, comprising:
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identifying a speech segment and a noise segment with regard to the received signal using the decoded information;
deriving a norm of the excitation signal at regular intervals in the noise segment;
smoothing the norm using a past value of the norm;
limiting the value of the smoothed norm based upon an amount of fluctuation derived from the norm and the smoothed norm;
changing the amplitude of the excitation signal in said intervals using the norm and the norm that has been smoothed and limited; and
driving the filter by the excitation signal the amplitude of which has been changed. - View Dependent Claims (13, 14, 15, 16, 17)
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18. A speech signal decoding apparatus for decoding information concerning at least a sound source signal, gain and linear prediction coefficients from a received signal, generating an excitation signal and linear prediction coefficients from the decoded information, and driving a filter, which is constituted by the linear predictions coefficients, by the excitation signal to thereby decode a speech signal, comprising:
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a smoothing circuit smoothing the gain using a past value of the gain; and
a smoothing-quantity limiting circuit limiting the value of the smoothed gain based upon an amount of fluctuation calculated from the gain and the smoothed gain. - View Dependent Claims (19, 20, 21)
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22. A speech signal decoding apparatus for decoding information concerning an excitation signal and linear prediction coefficients from a received signal, generating the excitation signal and linear prediction coefficients from the decoded information, and driving a filter, which is constituted by the linear prediction coefficients, by the excitation signal to thereby decode a speech signal, comprising:
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an excitation-signal normalizing circuit deriving a norm of the excitation signal at regular intervals and dividing the excitation signal by the norm;
a smoothing circuit smoothing the norm using a past value of the norm;
a smoothing-quantity limiting circuit limiting the value of the smoothed norm based upon an amount of fluctuation calculated from the norm and the smoothed norm; and
an excitation-signal reconstruction circuit multiplying the smoothed and limited norm by the excitation signal to thereby change the amplitude of the excitation signal in said intervals. - View Dependent Claims (23, 24, 25)
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26. A speech signal decoding apparatus for decoding information concerning an excitation signal and linear prediction coefficients from a received signal, generating the excitation signal and linear prediction coefficients from the decoded information, and driving a filter, which is constituted by the linear prediction coefficients, by the excitation signal to thereby decode a speech signal, comprising:
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a voiced/unvoiced identification circuit identifying a speech segment and a noise segment with regard to the received signal using the decoded information;
an excitation-signal normalizing circuit deriving a norm of the excitation signal at regular intervals and dividing the excitation signal by the norm;
a smoothing circuit smoothing the norm using a past value of the norm;
a smoothing-quantity limiting circuit limiting the value of the smoothed norm based upon an amount of fluctuation calculated from the norm and the smoothed norm; and
an excitation-signal reconstruction circuit multiplying the smoothed and limited norm by the excitation signal to thereby change the amplitude of the excitation signal in said intervals. - View Dependent Claims (27, 28, 29)
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30. A program product for causing a computer to execute processing (a) and (b) below, wherein the computer constitutes a speech signal decoding apparatus for decoding information concerning at least a sound source signal, gain and linear prediction coefficients from a received signal, generating an excitation signal and linear prediction coefficients from the decoded information, and driving a filter, which is constituted by the linear prediction coefficients, by the excitation signal to thereby decode a speech signal;
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(a) a process for performing smoothing using a past value of a gain and calculating an amount of fluctuation between the gain and a smoothed gain; and
(b) a process for limiting the value of the smoothed gain in conformity with the value of the amount of fluctuation and decoding the speech signal using the smoothed, limited gain. - View Dependent Claims (31, 32)
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33. A program product for causing a computer to execute processing (a) to (c) below, wherein the computer constitutes a speech signal decoding apparatus for decoding information concerning an excitation signal and linear prediction coefficients from a received signal, generating an excitation signal and linear prediction coefficients from the decoded information, and driving a filter, which is constituted by the linear prediction coefficients, by the excitation signal to thereby decode a speech signal:
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(a) calculating a norm of an excitation signal at regular intervals and smoothing the norm using a past value of the norm;
(b) limiting the value of the smoothed norm in conformity with the value of an amount of fluctuation calculated from the norm and the smoothed norm; and
(c) changing the amplitude of the excitation signal in said intervals using the norm and the norm that has been smoothed and limited, and driving the filter by the excitation signal the amplitude of which has been changed. - View Dependent Claims (34, 35, 36)
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37. A program product for causing a computer to execute processing (a) to (d) below, wherein the computer constitutes a speech signal decoding apparatus for decoding information concerning an excitation signal and linear prediction coefficients from a received signal, generating an excitation signal and linear prediction coefficients from the decoded information, and driving a filter, which is constituted by the linear prediction coefficients, by the excitation signal to thereby decode a speech signal:
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(a) identifying a speech segment and a noise segment with regard to a received signal using decoded information;
(b) calculating a norm of an excitation signal at regular intervals in the noise segment and smoothing the norm using a past value of the norm;
(c) limiting the value of the smoothed norm in conformity with an amount of fluctuation calculated from the norm and the smoothed norm; and
(d) changing the amplitude of the excitation signal in said intervals using the norm and the norm that has been smoothed and limited, and driving the filter by the excitation signal the amplitude of which has been changed. - View Dependent Claims (38, 39, 40)
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41. A speech signal decoding apparatus comprising:
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(a) a code input circuit splitting code of a bit sequence of an encoded input signal that enters from an input terminal, converting the code to indices that correspond to a plurality of decode parameters, outputting an index corresponding to a line spectrum pair, termed hereinafter “
LSP”
, which represents the frequency characteristic of the input signal, to an LSP decoding circuit, outputting an index corresponding to a delay that represents a pitch period of the input signal to a pitch signal decoding circuit, outputting an index corresponding to a sound source vector comprising a random number or a pulse train to a sound source signal decoding circuit, outputting an index corresponding to a first gain to a first gain decoding circuit, and outputting an index corresponding to a second gain to a second gain decoding circuit;
(b) an LSP decoding circuit, to which the index output from said code input circuit is input, and which reads the LSP corresponding to the input index out of a table which stores LSPs corresponding to indices, obtains an LSP in a subframe of the present frame and outputs the LSP;
(c) a linear prediction coefficient conversion circuit, to which the LSP output from said LSP decoding circuit is input, and which converts the LSP to linear prediction coefficients and outputs the coefficients to a synthesis filter;
(d) a sound source signal decoding circuit, to which the index output from said code input circuit is input, and which reads a sound source vector corresponding to the index out of a table storing sound source vectors corresponding to indices, and outputs the sound source vector to a second gain decoding circuit;
(e) a second gain decoding circuit, to which the index output from said code input circuit is input, and which reads a second gain corresponding to the input index out of a table storing second gains corresponding to indices, and outputs the second gain to a smoothing circuit;
(f) a second gain circuit, to which a first sound source vector output from said sound source signal decoding circuit and the second gain are input, and which multiplies the first sound source vector by the second gain to generate a second sound source vector and outputs the generated second sound source vector to an adder;
(g) a memory circuit holding an excitation vector input thereto from said adder and outputting a held excitation vector, which was input thereto in the past, to a pitch signal decoding circuit;
(h) a pitch signal decoding circuit, to which the past excitation vector held by said memory circuit and the index output from said code input circuit are input, with said index specifying a delay, and which cuts out vectors of samples corresponding to a vector length from a point previous to the starting point of the present frame by an amount corresponding to the delay to thereby generate a first pitch vector, and outputs the first pitch vector to a first gain circuit;
(i) a first gain decoding circuit, to which the index output from said code input circuit is input, and which reads a first gain corresponding to the input index out of a table storing first gains corresponding to indices, and outputs the first gain to a first gain circuit;
(j) a first gain circuit, to which the first pitch vector output from said pitch signal decoding circuit and the first gain output from said first gain decoding circuit are input, and which multiplies the input first pitch vector by the first gain to generate a second pitch vector, and outputs the generated second pitch vector to said adder;
(k) an adder, to which the second pitch vector output from said first gain circuit and the second sound source vector output from said second gain circuit are input, and which calculates the sum of these inputs, and outputs the sum to a synthesis filter as an excitation vector;
(l) a smoothing coefficient calculation circuit, to which LSP output from said LSP decoding circuit is input, and which calculates average LSP in the present frame, finds the amount of fluctuation of the LSP with respect to each subframe, finds a smoothing coefficient in the subframe, and outputs the smoothing coefficient to a smoothing circuit;
(m) a smoothing circuit, to which the smoothing coefficient output from said smoothing coefficient calculation circuit and the second gain output from said second gain decoding circuit are input, and which finds an average gain from the second gain in the subframe, and outputs the second gain;
(n) a synthesis filter, to which the excitation vector output from said adder and the linear prediction coefficients output from said linear prediction coefficient conversion circuit are input, and which drives a synthesis filter, for that the linear prediction coefficients have been set, by the excitation vector to thereby calculate a reconstructed vector, and outputs the reconstructed vector from an output terminal; and
(o) a smoothing-quantity limiting circuit, to which the second gain output from said second gain decoding circuit and the smoothed second gain output from said smoothing circuit are input, and which finds the amount of fluctuation between the smoothed second gain output from said smoothing circuit and the second gain output from said second gain decoding circuit, outputs the smoothed second gain to said second gain circuit as is when the amount of fluctuation is less than a predetermined threshold value, replaces the smoothed second gain with a smoothed second gain limited in terms of values it is capable of taking on when the amount of fluctuation is equal to or greater than the threshold value, and outputs this smoothed second gain to said second gain circuit. - View Dependent Claims (42, 43, 44, 45, 46)
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47. A speech signal decoding method for decoding information concerning at least a sound source signal, gain and linear prediction coefficients from a received signal, generating an excitation signal and linear prediction coefficients from decoded information, and driving a filter, which is constituted by the linear prediction coefficients, by the excitation signal to thereby decode a speech signal, comprising:
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smoothing the gain using a past value of the gain;
limiting the value of the smoothed gain based upon the gain prior to the smoothing and the smoothed gain; and
decoding the speech signal using the gain that has been smoothed and limited.
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48. A speech signal decoding method for decoding Information concerning an excitation signal and linear prediction coefficients from a received signal, generating an excitation signal and linear prediction coefficients from the decoded information, and driving a filter, which is constituted by the linear prediction coefficients, by the excitation signal to thereby decode a speech signal, comprising:
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deriving a norm of the excitation signal at regular intervals;
smoothing the norm using a past value of the norm;
limiting the value of the smoothed norm based upon the smoothed norm and the norm prior to the smoothing;
changing the amplitude of the excitation signal in said intervals using said norm and the norm that has been smoothed and limited; and
driving the filter by the excitation signal the amplitude of which has been changed.
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Specification