Patent US5732188A successfully refreshed from Google Patents.
US5732188A
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Method for the modification of LPC coefficients of acoustic signals
Assignee: NTT Inc
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Filing: 1996-03-11
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Granted: 1998-03-24
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Expires: 2016-03-11
Abstract
Abstract In a CELP coding scheme, p-order LPC coefficients of an input signal are transformed into n-order LPC cepctrum coefficients c j (S 2 ), which are modified into n-order modified LPC cepstrum coefficients c j ' (S 3 ). Log power spectral envelopes of the input signal and a masking function suited thereto are calculated (FIGS. 3B, C), then they are subjected to inverse Fourier transform to obtain n-order LPC cepstrum coefficients, respectively, (FIGS. 3D, E), then the relationship between corresponding orders of the LPC cepstrum coefficients is calculated, and the modification in step S 3 is carried out on the basis of the relationship. The modified coefficients c j are inversely transformed by the method of least squares into m-order LPC coefficients for use as filter coefficients of a perceptual weighting filter. This concept is applicable to a postfilter as well.
Inventors
- 👤 Takehiro Moriya
- 👤 Kazunori Mano
- 👤 Satoshi Miki
- 👤 Hitoshi Ohmura
- 👤 Shigeaki Sasaki
- 👤 Naoki Iwakami
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-04 13:30
CPC Classifications
G; G10; G10L; G10L19/00; G10L19/04; G10L19/06; G10L25/00; G10L25/03; G10L25/24
Claims Analysis
Total Claims: 20
Claim 1
Independent Claim
80 words
An LPC coefficient modifying method which transforms p-order LPC coefficients of an acoustic signal into n-order (where n>p) LPC cepstrum coefficients, then modifies said LPC cepstrum coefficients, and inversely transforms said modified LPC cepstrum coefficients into m-order (where m<n) LPC coefficients for use in controlling the characteristics of a filter, characterized in: that said transformation of said modified LPC cepstrum coefficients into said m-order LPC coefficients is performed by using the method of least squares in an LPC cepstrum domain.
Claim 2
Dependent Claim
80 words
An LPC coefficient modifying method which transforms p-order LPC coefficients of an acoustic signal into n-order (where n>p) LPC cepstrum coefficients, then modifies said LPC cepstrum coefficients, and inversely transforms said modified LPC cepstrum coefficients into m-order (where m<n) LPC coefficients for use in controlling the characteristics of a filter, characterized in: that said transformation of said modified LPC cepstrum coefficients into said m-order LPC coefficients is performed by using the method of least squares in an LPC cepstrum domain.
Claim 3
Dependent Claim
26 words
The method of claim 1, characterized in: that said modification of said LPC cepstrum coefficients is to multiply each order (each element) of them by 0.5.
Claim 4
Dependent Claim
49 words
The method of claim 2, characterized in: that said p-order LPC coefficients are to determine filter coefficients of a synthesis filter; and that said inversely transformed LPC coefficients are used to determine filter coefficients of two cascaded filter sections of the same characteristic for use as said synthesis filter.
Claim 5
Dependent Claim
157 words
An LPC coefficient modifying method which is used in a coding scheme that obtains a spectral envelope of an input acoustic signal by an LPC analysis and determines coded data of said input acoustic signal in a manner to minimize a difference signal between said input signal and an LPC synthesized signal of said coded data and which modifies LPC coefficients for use as filter coefficients of an all-pole or moving average digital filter that weights said difference signal according to human perceptual or psycho-acoustic characteristics, said method comprising the steps of: transforming p-order LPC coefficients, obtained by said LPC analysis of said input acoustic signal, into n-order (where n>p) LPC cepstrum coefficients; modifying said n-order LPC cepstrum coefficients into n-order modified LPC cepstrum coefficients; and inversely transforming said n-order modified LPC cepstrum coefficients, by the method of least squares, into new m-order (where m<n) LPC coefficients to obtain LPC coefficients for use as said filter coefficients.
Claim 6
Dependent Claim
157 words
An LPC coefficient modifying method which is used in a coding scheme that obtains a spectral envelope of an input acoustic signal by an LPC analysis and determines coded data of said input acoustic signal in a manner to minimize a difference signal between said input signal and an LPC synthesized signal of said coded data and which modifies LPC coefficients for use as filter coefficients of an all-pole or moving average digital filter that weights said difference signal according to human perceptual or psycho-acoustic characteristics, said method comprising the steps of: transforming p-order LPC coefficients, obtained by said LPC analysis of said input acoustic signal, into n-order (where n>p) LPC cepstrum coefficients; modifying said n-order LPC cepstrum coefficients into n-order modified LPC cepstrum coefficients; and inversely transforming said n-order modified LPC cepstrum coefficients, by the method of least squares, into new m-order (where m<n) LPC coefficients to obtain LPC coefficients for use as said filter coefficients.
Claim 7
Dependent Claim
204 words
An LPC coefficient modifying method which is used in a coding scheme that obtains a spectral envelope of an input acoustic signal by an LPC analysis and determines coded data of said input acoustic signal in a manner to minimize a difference signal between said input signal and an LPC synthesized signal of said coded indexes and which modifies LPC coefficients for use as filter coefficients of a digital filter that performs an LPC synthesis of said synthesized signal and weights said difference signal according to human perceptual or psycho-acoustic characteristics, said method comprising the steps of: quantizing p-order LPC coefficients, obtained by said LPC analysis of said input acoustic signal, into quantized LPC coefficients; transforming both of said LPC coefficients and quantized LPC coefficients into n-order LPC cepstrum coefficients, respectively; modifying said n-order LPC cepstrum coefficients, transformed from said LPC coefficients, into n-order modified LPC cepstrum coefficients; adding said n-order LPC cepstrum coefficients, transformed from said quantized LPC coefficients, and said modified LPC cepstrum coefficients into n-order added LPC cepstrum coefficient; and inversely transforming said n-order added LPC cepstrum coefficients by the method of least squares into new m-order (where m<n) LPC coefficients to obtain LPC coefficients for use as said filter coefficients.
Claim 8
Dependent Claim
204 words
An LPC coefficient modifying method which is used in a coding scheme that obtains a spectral envelope of an input acoustic signal by an LPC analysis and determines coded data of said input acoustic signal in a manner to minimize a difference signal between said input signal and an LPC synthesized signal of said coded indexes and which modifies LPC coefficients for use as filter coefficients of a digital filter that performs an LPC synthesis of said synthesized signal and weights said difference signal according to human perceptual or psycho-acoustic characteristics, said method comprising the steps of: quantizing p-order LPC coefficients, obtained by said LPC analysis of said input acoustic signal, into quantized LPC coefficients; transforming both of said LPC coefficients and quantized LPC coefficients into n-order LPC cepstrum coefficients, respectively; modifying said n-order LPC cepstrum coefficients, transformed from said LPC coefficients, into n-order modified LPC cepstrum coefficients; adding said n-order LPC cepstrum coefficients, transformed from said quantized LPC coefficients, and said modified LPC cepstrum coefficients into n-order added LPC cepstrum coefficient; and inversely transforming said n-order added LPC cepstrum coefficients by the method of least squares into new m-order (where m<n) LPC coefficients to obtain LPC coefficients for use as said filter coefficients.
Claim 9
Dependent Claim
63 words
The method of claim 4 or 5, characterized in: that said modifying step is a step of calculating the relationship between said input acoustic signal and a masking function, which corresponds thereto and is based on human perceptual or psycho-acoustic characteristics, in the domain of said n-order LPC cepstrum coefficients and modifying said n-order LPC cepstrum coefficients on the basis of said relationship.
Claim 10
Dependent Claim
42 words
The method of claim 6, characterized in: that said modifying step is a step of modifying said LPC cepstrum coefficients c j (where j=1, 2, . . . , n) by multiplying them by a constant β j based on said relationship.
Claim 11
Dependent Claim
92 words
The method of claim 7, characterized in: said modifying step is a step of determining q (where q is an integer equal to or greater than 2) positive constants γ k (where k=1, . . . , q) equal to or smaller than 1 on the basis of said relationship, then multiplying said n-order LPC cepstrum coefficients c j (where j=1, 2, . . . , n) by γ k j to obtain q LPC cepstrum coefficients, and adding or subtracting said q LPC cepstrum coefficients on the basis of said relationship.
Claim 12
Dependent Claim
20 words
The method of claim 4 or 5, characterized in: that said m is a value nearly equal to said p.
Claim 13
Independent Claim
103 words
A method which modifies LPC coefficients for use as filter coefficients of an all-pole or moving average digital filter that processes a decoded synthesized signal of coded input data of an acoustic signal to suppress quantization noise, said method comprising the steps of: transforming p-order LPC coefficients, derived from said input indexes, into n-order (where n>p) LPC cepstrum coefficients; modifying said n-order LPC cepstrum coefficients into n-order modified LPC cepstrum coefficients; and inversely transforming said n-order LPC cepstrum coefficients, by the method of least squares, into new m-order (where m<n) LPC coefficients to obtain said LPC coefficients for use as said filter coefficients.
Claim 14
Independent Claim
103 words
A method which modifies LPC coefficients for use as filter coefficients of an all-pole or moving average digital filter that processes a decoded synthesized signal of coded input data of an acoustic signal to suppress quantization noise, said method comprising the steps of: transforming p-order LPC coefficients, derived from said input indexes, into n-order (where n>p) LPC cepstrum coefficients; modifying said n-order LPC cepstrum coefficients into n-order modified LPC cepstrum coefficients; and inversely transforming said n-order LPC cepstrum coefficients, by the method of least squares, into new m-order (where m<n) LPC coefficients to obtain said LPC coefficients for use as said filter coefficients.
Claim 15
Independent Claim
112 words
A method which modifies LPC coefficients for use as filter coefficients of a digital filter that uses p-order LPC coefficients in coded input data of an acoustic signal to simultaneously synthesize a signal and perceptually suppress quantization noise, said method comprising the steps of: transforming said p-order LPC coefficients into n-order (where n>p) LPC cepstrum coefficients; modifying said n-order LPC cepstrum coefficients into n-order modified LPC cepstrum coefficients; adding said n-order LPC cepstrum coefficients and said n-order modified LPC cepstrum coefficients; and transforming said added LPC cepstrum coefficients, by the method of least squares, into new m-order (where m<n) LPC coefficients to obtain said LPC coefficients for use as said filter coefficients.
Claim 16
Independent Claim
112 words
A method which modifies LPC coefficients for use as filter coefficients of a digital filter that uses p-order LPC coefficients in coded input data of an acoustic signal to simultaneously synthesize a signal and perceptually suppress quantization noise, said method comprising the steps of: transforming said p-order LPC coefficients into n-order (where n>p) LPC cepstrum coefficients; modifying said n-order LPC cepstrum coefficients into n-order modified LPC cepstrum coefficients; adding said n-order LPC cepstrum coefficients and said n-order modified LPC cepstrum coefficients; and transforming said added LPC cepstrum coefficients, by the method of least squares, into new m-order (where m<n) LPC coefficients to obtain said LPC coefficients for use as said filter coefficients.
Claim 17
Dependent Claim
68 words
The method of claim 10 or 11, characterized in: that said modifying step is a step of calculating the relationship between a decoded synthesized signal of said input data and an enhancement characteristic function, which corresponds thereto and is based on human perceptual or psycho-acoustic characteristics, in the domain of said n-order LPC cepstrum coefficients and modifying said n-order LPC cepstrum coefficients on the basis of said relationship.
Claim 18
Dependent Claim
42 words
The method of claim 12, characterized in: that said modifying step is a step of modifying said LPC cepstrum coefficients c j (where j=1, 2, . . . , n) by multiplying them by a constant β j based on said relationship.
Claim 19
Dependent Claim
93 words
The method of claim 12, characterized in: that said modifying step is a step of determining q (where q is an integer equal to or greater than 2) positive constants γ k (where k=1, . . . , q) equal to or smaller than 1 on the basis of said relationship, then multiplying said n-order LPC cepstrum coefficients c j (where j=1, 2, . . . , n) by γ k j to obtain q LPC cepstrum coefficients, and adding or subtracting said q LPC cepstrum coefficients on the basis of said relationship.
Claim 20
Dependent Claim
18 words
The method of claim 12, characterized in: that said m is a value nearly equal to said p.
References Cited (Backward Citations)
US4811376A
Cited
EP0562777A1
Cited
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