FREQUENCY DOMAIN PARAMETER SEQUENCE GENERATING METHOD, ENCODING METHOD, DECODING METHOD, FREQUENCY DOMAIN PARAMETER SEQUENCE GENERATING APPARATUS, ENCODING APPARATUS, DECODING APPARATUS, PROGRAM, AND RECORDING MEDIUM

• US 20170249947A1
• Filed: 02/16/2015
• Published: 08/31/2017
• Est. Priority Date: 04/24/2014
• Status: Active Grant

• Current Assignee: Nippon Telegraph and Telephone Corporation, University of Tokyo
• Original Assignee: Nippon Telegraph and Telephone Corporation, University of Tokyo
• Inventors: MORIYA, Takehiro, KAMAMOTO, Yutaka, HARADA, Noboru, KAMEOKA, Hirokazu, SUGIURA, Ryosuke
• Granted Patent: US 10,332,533 B2
• Time in Patent Office: Days
• CPC Class Codes: G10L 19/02 using spectral analysis, e.g. transform vocoders or subband vocoders
• CPC Class Codes: G10L 19/07 Line spectrum pair [LSP] vocoders
• CPC Class Codes: G10L 19/12 the excitation function being a code excitation, e.g. in code excited linear prediction [CELP] vocoders
• CPC Class Codes: G10L 25/06 the extracted parameters being correlation coefficients
• CPC Class Codes: G10L 25/12 the extracted parameters being prediction coefficients

Abstract

The present invention reduces encoding distortion in frequency domain encoding compared to conventional techniques, and obtains LSP parameters that correspond to quantized LSP parameters for the preceding frame and are to be used in time domain encoding from coefficients equivalent to linear prediction coefficients resulting from frequency domain encoding. When p is an integer equal to or greater than 1, a linear prediction coefficient sequence which is obtained by linear prediction analysis of audio signals in a predetermined time segment is represented as a[1], a[2], . . . , a[p], and ω[1], ω[2], . . . , ω[p] are a frequency domain parameter sequence derived from the linear prediction coefficient sequence a[1], a[2], . . . , a[p], an LSP linear transformation unit (300) determines the value of each converted frequency domain parameter ˜ω[i] (i=1, 2, . . . , p) in a converted frequency domain parameter sequence ˜ω[1], ˜ω[2], . . . , ˜ω[p] using the frequency domain parameter sequence ω[1], ω[2], . . . , ω[p] as input, through linear transformation which is based on the relationship of values between ω[i] and one or more frequency domain parameters adjacent to ω[i].

Claims

1. A frequency domain parameter sequence generating method comprising:

where p is an integer equal to or greater than 1, γ

1 is a positive constant equal to or smaller than 1, a linear prediction coefficient sequence which is obtained by linear prediction analysis of audio signals in a predetermined time segment is represented as a[1], a[2], . . . , a[p], and ω

[1], ω

[2], . . . , ω

[p] are a frequency domain parameter sequence derived from the linear prediction coefficient sequence a[1], a[2], . . . , a[p],

a parameter sequence conversion step of determining a converted frequency domain parameter sequence ˜

ω

[1], ˜

ω

[2], . . . , ˜

ω

[p] using the frequency domain parameter sequence ω

[1], ω

[2], . . . , ω

[p] as input, wherein

the parameter sequence conversion step determines a value of each converted frequency domain parameter ˜

ω

[i] (i−

1, 2, . . . , p) in the converted frequency domain parameter sequence ˜

ω

[1], ˜

ω

[2], . . . , ˜

ω

[p] through linear transformation which is based on a relationship of values between ω

[i] and one or more frequency domain parameters adjacent to ω

[i], and

each ω

[i] (i=1, 2, . . . , p) in the frequency domain parameter sequence ω

[1], ω

[2], . . . , ω

[p] is a frequency domain parameter equivalent to a<sub>γ

1</sub>[1], a<sub>γ

1</sub>[2], . . . , a<sub>γ

1</sub>[p], or a quantized value of said frequency domain parameter, where a<sub>γ

1</sub>[i]=a[i]×

(γ

1)ⁱ.

2. The frequency domain parameter sequence generating method according to claim 1, wherein

the linear transformation is linear transformation that makes intervals between parameter values more uniform or less uniform in the converted frequency domain parameter sequence than in the frequency domain parameter sequence ω

[1], ω

[2], . . . , ω

[p].

10. A encoding method including the steps of the frequency domain parameter sequence generating method according to any one of claims 1 to 8, the encoding method comprising:

where γ

is a adjustment factor which is a positive constant equal to or smaller than 1,

a linear prediction coefficient adjustment step of generating a adjusted linear prediction coefficient sequence a_γ

[1], a_γ

[2], . . . , a_γ

[p] by adjusting the linear prediction coefficient sequence a[1], a[2], . . . , a[p] using the adjustment factor γ

;

a adjusted LSP generation step of generating a adjusted LSP parameter sequence θ

_γ

[1], θ

_γ

[2], . . . , θ

_γ

[p] using the adjusted linear prediction coefficient sequence a_γ

[1], a_γ

[2], . . . , a_γ

[p];

a adjusted LSP encoding step of encoding the adjusted LSP parameter sequence θ

_γ

[1], θ

_γ

[2], . . . , θ

_γ

[p] to generate adjusted LSP codes and a adjusted quantized LSP parameter sequence ̂

θ

_γ

[1], ̂

θ

_γ

[2], . . . , ̂

θ

_γ

[p] corresponding to the adjusted LSP codes;

an LSP linear transformation step of, with the frequency domain parameter sequence ω

[1], ω

[2], . . . , ω

[p] being the adjusted quantized LSP parameter sequence ̂

θ

_γ

[1], ̂

θ

_γ

[2], . . . , ̂

θ

_γ

[p], and γ

1=γ and

γ

2=1, executing the parameter sequence conversion step to thereby generate the converted frequency domain parameter sequence ˜

ω

[1], ˜

ω

[2], . . . , ω

[p] as an approximate quantized LSP parameter sequence ̂

θ

_app[1], ̂

θ

_app[2], . . . , ̂

θ

_app[p];

a quantized linear prediction coefficient sequence generation step of generating a adjusted quantized linear prediction coefficient sequence ̂

a_γ

[1], ̂

a_γ

[2], . . . , ̂

a_γ

[p] by converting the adjusted quantized LSP parameter sequence ̂

θ

_γ

[1], ̂

θ

_γ

[2], . . . , ̂

θ

_γ

[p] into linear prediction coefficients;

a quantized smoothed power spectral envelope series calculation step of calculating a quantized smoothed power spectral envelope series ̂

W_γ

[1], ̂

W_γ

[2], . . . , ̂

W_γ

[N] which is a series in frequency domain corresponding to the adjusted quantized linear prediction coefficient sequence ̂

a_γ

[1], ̂

a_γ

[2], . . . , ̂

a_γ

[p];

a frequency domain encoding step of generating frequency domain signal codes by encoding a frequency domain sample sequence X[1], X[2], . . . , X[N] corresponding to the audio signals using the quantized smoothed power spectral envelope series ̂

W_γ

[1], ̂

W_γ

[2], . . . , ̂

W_γ

[N];

an LSP generation step of generating an LSP parameter sequence θ

[1], θ

[2], . . . , e[p] using the linear prediction coefficient sequence a[1], a[2], . . . , a[p];

an LSP encoding step of encoding the LSP parameter sequence θ

[1], θ

[2], . . . , θ

[p] to generate LSP codes and a quantized LSP parameter sequence ̂

θ

[1], ̂

θ

[2], . . . , ̂

θ

[p] corresponding to the LSP codes; and

a time domain encoding step of encoding the audio signals to generate time domain signal codes using either a quantized LSP parameter sequence obtained in the LSP encoding step for a preceding time segment or an approximate quantized LSP parameter sequence obtained in the LSP linear transformation step for the preceding time segment, and the quantized LSP parameter sequence for the predetermined time segment.

11. A encoding method including the steps of the frequency domain parameter sequence generating method according to any one of claims 1 to 8, the encoding method comprising:

where γ

is a adjustment factor which is a positive constant equal to or smaller than 1,

a linear prediction coefficient adjustment step of generating a adjusted linear prediction coefficient sequence a_γ

[1], a_γ

[2], . . . , a_γ

[p] by adjusting the linear prediction coefficient sequence a[1], a[2], . . . , a[p] using the adjustment factor γ

;

a adjusted LSP generation step of generating a adjusted LSP parameter sequence θ

_γ

[1], θ

_γ

[2], . . . , θ

_γ

[p] using the adjusted linear prediction coefficient sequence a_γ

[1], a_γ

[2], . . . , a_γ

[p];

a adjusted LSP encoding step of encoding the adjusted LSP parameter sequence θ

_γ

[1], θ

_γ

[2], . . . , θ

_γ

[p] to generate adjusted LSP codes and a adjusted quantized LSP parameter sequence ̂

θ

_γ

[1], ̂

θ

_γ

[2], . . . , ̂

θ

_γ

[p] corresponding to the adjusted LSP codes;

an LSP linear transformation step of, with the frequency domain parameter sequence ω

[1], ω

[2], . . . , ω

[p] being the adjusted quantized LSP parameter sequence ̂

θ

_γ

[1], ̂

θ

_γ

[2], . . . , ̂

θ

_γ

[p], and γ

1=γ and

γ

2=1, executing the parameter sequence conversion step to thereby generate the converted frequency domain parameter sequence ˜

ω

[1], ˜

ω

[2], . . . , ˜

ω

[p] as an approximate quantized LSP parameter sequence ̂

θ

_app[1], ̂

θ

_app[2], . . . , ̂

θ

_app[p];

a quantized smoothed power spectral envelope series calculation step of calculating a quantized smoothed power spectral envelope series ̂

W_γ

[1], ̂

W_γ

[2], . . . , ̂

W_γ

[N] based on the adjusted quantized LSP parameter sequence ̂

θ

_γ

[1], ̂

θ

_γ

[2], . . . , ̂

θ

_γ

[p];

a frequency domain encoding step of generating frequency domain signal codes by encoding a frequency domain sample sequence X[1], X[2], X[N] corresponding to the audio signals using the quantized smoothed power spectral envelope series ̂

W_γ

[1], ̂

W_γ

[2], . . . , ̂

W_γ

[N];

an LSP generation step of generating an LSP parameter sequence θ

[1], θ

[2], . . . , θ

[p] using the linear prediction coefficient sequence a[1], a[2], . . . , a[p];

an LSP encoding step of encoding the LSP parameter sequence θ

[1], θ

[2], . . . , θ

[p] to generate LSP codes and a quantized LSP parameter sequence ̂

θ

[1], ̂

θ

[2], . . . , ̂

θ

[p] corresponding to the LSP codes; and

a time domain encoding step of encoding the audio signals to generate time domain signal codes using either a quantized LSP parameter sequence obtained in the LSP encoding step for a preceding time segment or an approximate quantized LSP parameter sequence obtained in the LSP linear transformation step for the preceding time segment, and the quantized LSP parameter sequence for the predetermined time segment.

12. The encoding method according to claim 10, further comprising:

an output step of outputting either the frequency domain signal codes generated in the frequency domain encoding step or the time domain signal codes generated in the time domain encoding step, wherein

at the time domain encoding step,

when frequency domain signal codes have been output in the output step for the preceding time segment, encoding that uses the approximate quantized LSP parameter sequence obtained in the LSP linear transformation step for the preceding time segment is performed, and

when time domain signal codes have been output in the output step for the preceding time segment, encoding that uses the quantized LSP parameter sequence obtained in the LSP generation step for the preceding time segment is performed.

13. A decoding method including the steps of the frequency domain parameter sequence generating method according to any one of claims 1 to 8, the decoding method comprising:

a adjusted LSP code decoding step of decoding input adjusted LSP codes to obtain a decoded adjusted LSP parameter sequence ̂

θ

_γ

[1], Aθ

_γ

[2], . . . , ̂

θ

_γ

[p];

a decoded LSP linear transformation step of, with the frequency domain parameter sequence ω

[1], ω

[2], . . . , ω

[p] being the decoded adjusted LSP parameter sequence ̂

θ

_γ

[1], ̂

θ

_γ

[2], . . . , ̂

θ

_γ

[p], and γ

1=γ and

γ

2=1, executing the parameter sequence conversion step to thereby generate the converted frequency domain parameter sequence ˜

ω

[1], ˜

ω

[2], . . . , ˜

ω

[p] as a decoded approximate LSP parameter sequence ̂

θ

_app[1], ̂

θ

_app[2], . . . , ̂

θ

_app[p];

a decoded linear prediction coefficient sequence generation step of generating a decoded adjusted linear prediction coefficient sequence ̂

a_γ

[1], ̂

a_γ

[2], . . . , ̂

a_γ

[p] by converting the decoded adjusted LSP parameter sequence ̂

θ

_γ

[1], ̂

θ

_γ

[2], . . . , ̂

θ

_γ

[p] into linear prediction coefficients;

a decoded smoothed power spectral envelope series calculation step of calculating a decoded smoothed power spectral envelope series ̂

W_γ

[1], ̂

W_γ

[2], ̂

W_γ

[N] which is a series in frequency domain corresponding to the decoded adjusted linear prediction coefficient sequence ̂

a_γ

[1], ̂

a_γ

[2], . . . , ̂

a_γ

[p];

a frequency domain decoding step of generating decoded sound signals using a frequency domain signal sequence resulting from decoding of input frequency domain signal codes and the decoded smoothed power spectral envelope series ̂

W_γ

[1], ̂

W_γ

[2], . . . , ̂

W_γ

[N];

an LSP code decoding step of decoding input LSP codes to obtain a decoded LSP parameter sequence ̂

θ

[1], ̂

θ

[2], . . . , ̂

θ

[p]; and

a time domain decoding step of decoding input time domain signal codes, and generating decoded sound signals by synthesizing the time domain signal codes using either the decoded LSP parameter sequence obtained in the LSP code decoding step for the preceding time segment or the decoded approximate LSP parameter sequence obtained in the LSP linear transformation step for the preceding time segment, and the decoded LSP parameter sequence for the predetermined time segment.

14. A decoding method including the steps of the frequency domain parameter sequence generating method according to any one of claims 1 to 8, the decoding method comprising:

a adjusted LSP code decoding step of decoding input adjusted LSP codes to obtain a decoded adjusted LSP parameter sequence ̂

θ

_γ

[1], ̂

θ

_γ

[2], . . . , ̂

θ

_γ

[p];

a decoded LSP linear transformation step of, with the frequency domain parameter sequence ω

[1], ω

[2], . . . , ω

[p] being the decoded adjusted LSP parameter sequence ̂

θ

_γ

[1], ̂

a_γ

[2], ̂

θ

_γ

[p], and γ

1=γ and

γ

2=1, executing the parameter sequence conversion step to thereby generate the converted frequency domain parameter sequence ˜

ω

[1], ˜

ω

[2], . . . , ˜

ω

[p] as a decoded approximate LSP parameter sequence ̂

θ

_app[1], ̂

θ

_app[2], . . . , ̂

θ

_app[p];

a decoded smoothed power spectral envelope series calculation step of calculating a decoded smoothed power spectral envelope series ̂

W_γ

[1], ̂

W_γ

[2], . . . , ̂

W_γ

[N] based on the decoded adjusted LSP parameter sequence ̂

θ

_γ

[1], ̂

θ

_γ

[2], . . . , ̂

θ

_γ

[p];

a frequency domain decoding step of generating decoded sound signals using the frequency domain signal sequence resulting from decoding of input frequency domain signal codes and the decoded smoothed power spectral envelope series ̂

W_γ

[1], ̂

W_γ

[2], . . . , ̂

W_γ

[N];

a frequency domain decoding step of generating decoded sound signals using the frequency domain signal sequence resulting from decoding of the input frequency domain signal codes and the decoded smoothed power spectral envelope series ̂

W_γ

[1], ̂

W_γ

[2], . . . , ̂

W_γ

[N];

an LSP code decoding step of decoding input LSP codes to obtain a decoded LSP parameter sequence ̂

θ

[1], ̂

θ

[2], . . . , ̂

[p]; and

a time domain decoding step of decoding input time domain signal codes, and generating decoded sound signals by synthesizing the time domain signal codes using either the decoded LSP parameter sequence obtained in the LSP code decoding step for the preceding time segment or the decoded approximate LSP parameter sequence obtained in the LSP linear transformation step for the preceding time segment, and the decoded LSP parameter sequence for the predetermined time segment.

26. A program for causing a computer to carry out the steps of the frequency domain parameter sequence generating method according to any one of claims 1, 3, 5, 7, and 8.

29. A non-transitory computer-readable recording medium having a program recorded thereon for causing a computer to carry out the steps of the frequency domain parameter sequence generating method according to any one of claims 1, 3, 5, 7, and 8.

32. The encoding method according to claim 11, further comprising:

an output step of outputting either the frequency domain signal codes generated in the frequency domain encoding step or the time domain signal codes generated in the time domain encoding step, wherein

at the time domain encoding step,

when frequency domain signal codes have been output in the output step for the preceding time segment, encoding that uses the approximate quantized LSP parameter sequence obtained in the LSP linear transformation step for the preceding time segment is performed, and

when time domain signal codes have been output in the output step for the preceding time segment, encoding that uses the quantized LSP parameter sequence obtained in the LSP generation step for the preceding time segment is performed.

3. A frequency domain parameter sequence generating method comprising:

where p is an integer equal to or greater than 1, and a linear prediction coefficient sequence obtained by linear prediction analysis of audio signals in a predetermined time segment is represented as a[1], a[2], . . . , a[p];

ω

[1], ω

[2], ω

[p] is one of

an LSP parameter sequence derived from the linear prediction coefficient sequence a[1], a[2], . . . , a[p],

an ISP parameter sequence derived from the linear prediction coefficient sequence a[1], a[2], . . . , a[p],

an ISF parameter sequence derived from the linear prediction coefficient sequence a[1], a[2], . . . , a[p],

an ISF parameter sequence derived from the linear prediction coefficient sequence a[1], a[2], . . . , a[p], and

a frequency domain parameter sequence which is derived from the linear prediction coefficient sequence a[1], a[2], . . . , a[p] and in which all of ω

[1], ω

[2], . . . , ω

[p−

1] are present from 0 to π and

, when all of linear prediction coefficients contained in the linear prediction coefficient sequence are 0, ω

[1], ω

[2], . . . , ω

[p−

1] are present from 0 to π

at equal intervals; and

each γ

1 and γ

2 is a positive constant equal to or smaller than 1, and K is a predetermined p×

p band matrix in which diagonal elements and elements that neighbor the diagonal elements in row direction have non-zero values,

a parameter sequence conversion step of generating a converted frequency domain parameter sequence ˜

ω

[1], ˜

ω

[2], . . . , ˜

ω

[p] defined by a following formula.

4. The frequency domain parameter sequence generating method according to claim 3, wherein

the band matrix K has positive values in the diagonal elements and negative values in elements that neighbor the diagonal elements in row direction.

6. The frequency domain parameter sequence generating method according to claim 3, wherein

the band matrix K has values greater than or equal to 0 in diagonal elements and values smaller than or equal to 0 in elements that neighbor the diagonal elements in row direction.

9. The frequency domain parameter sequence generating method according to any one of claims 3 to 6, wherein

γ

1 is a positive constant equal to or smaller than 1, and

each ω

[i] (i=1, 2, . . . , p) in the frequency domain parameter sequence ω

[1], ω

[2], . . . , ω

[p] is a frequency domain parameter equivalent to a<sub>γ

1</sub>[1], a<sub>γ

1</sub>[2], . . . , a<sub>γ

1</sub>[p], or a quantized value of said frequency domain parameter, where a<sub>γ

1</sub>[i]=a[i]×

(γ

1)ⁱ.

5. A frequency domain parameter sequence generating method comprising:

where p is an integer equal to or greater than 1, a linear prediction coefficient sequence which is obtained by linear prediction analysis of audio signals in a predetermined time segment is represented as a[1], a[2], . . . , a[p], and ω

[1], ω

[2], . . . , ω

[p] are a frequency domain parameter sequence which is derived from the linear prediction coefficient sequence a[1], a[2], . . . , a[p] and in which all of ω

[1], ω

[2], . . . , ω

[p−

1] are present from 0 to π and

, when all of linear prediction coefficients contained in the linear prediction coefficient sequence are 0, ω

[1], ω

[2], . . . , ω

[p−

1] are present from 0 to π

at equal intervals, and

where each γ

1 and γ

2 is a positive constant equal to or smaller than 1, and K is a predetermined p×

p band matrix in which diagonal elements and elements that neighbor the diagonal elements in row direction have non-zero values,

a parameter sequence conversion step of determining a converted frequency domain parameter sequence ˜

ω

[1], ˜

θ

[2], . . . , ˜

ω

[p] using the frequency domain parameter sequence ω

[1], θ

[2], . . . , ω

[p] as input, wherein

the parameter sequence conversion step determines each ˜

ω

[i] (i=1, 2, . . . , p) in the converted frequency domain parameter sequence ˜

ω

[1], ˜

ω

[2], . . . , ˜

ω

[p] such that

when ω

[i] is closer to ω

[i+1] relative to a midpoint between ω

[i+1] and ω

[i−

1], then ˜

ω

[i] is determined so that ˜

ω

[i] will be closer to ˜

ω

[i+1] relative to the midpoint between ˜

ω

[i+1] and ˜

ω

[i−

1] and that a value of ˜

ω

[i+1]−

˜

ω

[i] will be smaller than ω

[i+1]−

ω

[i], and

when ω

[i] is closer to ω

[i−

1] relative to the midpoint between ω

[i+1] and ω

[i−

1], then ˜

ω

[i] is determined so that ˜

ω

[i] will be closer to ˜

ω

[i−

1] relative to the midpoint between ˜

ω

[i+1] and ˜

ω

[i−

1] and that the value of ˜

ω

[i]−

˜

ω

[i−

1] will be smaller than ω

[i]−

ω

[i−

1], and

a converted frequency domain parameter sequence ˜

ω

[1], ˜

θ

[2], . . . , ˜

θ

[p] defined by

7. A frequency domain parameter sequence generating method comprising:

where p is an integer equal to or greater than 1, γ

1 is a positive constant equal to or smaller than 1, a linear prediction coefficient sequence which is obtained by linear prediction analysis of audio signals in a predetermined time segment is represented as a[1], a[2], . . . , a[p], and ω

[1], ω

[2], . . . , ω

[p] are a frequency domain parameter sequence derived from the linear prediction coefficient sequence a[1], a[2], . . . , a[p],

a parameter sequence conversion step of determining a converted frequency domain parameter sequence ˜

ω

[1], ˜

ω

[2], . . . , ˜

ω

[p] using the frequency domain parameter sequence ω

[1], ω

[2], . . . , ω

[p] as input, wherein

the parameter sequence conversion step determines each ˜

ω

[i] (i=1, 2, . . . , p) in the converted frequency domain parameter sequence ˜

ω

[1], ˜

ω

[2], . . . , ˜

ω

[p] such that

when ω

[i] is closer to ω

[i+1] relative to a midpoint between ω

[i+1] and ω

[i−

1], then ˜

ω

[i] is determined so that ˜

ω

[i] will be closer to ˜

ω

[i+1] relative to the midpoint between ˜

ω

[i+1] and ˜

ω

[i−

1] and that a value of ˜

ω

[i+1]−

˜

ω

[i] will be smaller than ω

[i+1]−

ω

[i], and

when ω

[i] is closer to ω

[i−

1] relative to the midpoint between ω

[i+1] and ω

[i−

1], then ˜

ω

[i] is determined so that ˜

ω

[i] will be closer to ˜

ω

[i−

1] relative to the midpoint between ˜

ω

[i+1] and ˜

ω

[i−

1] and that the value of ˜

ω

[i]−

˜

ω

[i−

1] will be smaller than ω

[i]−

ω

[i−

1], and

each ω

[i] (i=1, 2, . . . , p) in the frequency domain parameter sequence ω

[1], ω

[2], . . . , ω

[p] is a frequency domain parameter equivalent to a<sub>γ

1</sub>[1], a<sub>γ

2</sub>[2], . . . , a<sub>γ

1</sub>[p], or a quantized value of said frequency domain parameter, where a<sub>γ

1</sub>[i]=a[i]×

(γ

1)ⁱ.

8. A frequency domain parameter sequence generating method comprising:

where p is an integer equal to or greater than 1, γ

1 is a positive constant equal to or smaller than 1, a linear prediction coefficient sequence which is obtained by linear prediction analysis of audio signals in a predetermined time segment is represented as a[1], a[2], . . . , a[p], and ω

[1], ω

[2], . . . , ω

[p] are a frequency domain parameter sequence derived from the linear prediction coefficient sequence a[1], a[2], . . . , a[p],

a parameter sequence conversion step of determining a converted frequency domain parameter sequence ˜

ω

[1], ˜

ω

[2], . . . , ˜

ω

[p] using the frequency domain parameter sequence ω

[1], ω

[2], . . . , ω

[p] as input, wherein

the parameter sequence conversion step determines each ˜

ω

[i] (i=1, 2, . . . , p) in the converted frequency domain parameter sequence ˜

ω

[1], ˜

ω

[2], . . . , ˜

ω

[p] such that

when ω

[i] is closer to ω

[i+1] relative to the midpoint between ω

[i+1] and ω

[i−

1], then ˜

ω

[i] is determined so that ˜

ω

[i] will be closer to ˜

ω

[i+1] relative to the midpoint between ˜

ω

[i+1] and ˜

ω

[i−

1] and that a value of ˜

ω

[i+1]−

˜

ω

[i] will be greater than ω

[i+1]−

ω

[i], and

when ω

[i] is closer to ω

[i−

1] relative to the midpoint between ω

[i+1] and ω

[i−

1], then ˜

ω

[i] is determined so that ˜

ω

[i] will be closer to ˜

ω

[i−

1] relative to the midpoint between ˜

ω

[i+1] and ˜

ω

[i−

1] and that the value of ˜

ω

[i]−

˜

ω

[i−

1] will be greater than ω

[i]−

ω

[i−

1], and

each ω

[i] (i=1, 2, p) in the frequency domain parameter sequence ω

[1], ω

[2], . . . , ω

[p] is a frequency domain parameter equivalent to a<sub>γ

1</sub>[1], a<sub>γ

1</sub>[2], . . . , a<sub>γ

1</sub>[p], or a quantized value of said frequency domain parameter, where a<sub>γ

1</sub>[i]=a[i]×

(γ

1)ⁱ.

15. A frequency domain parameter sequence generating apparatus comprising:

where p is an integer equal to or greater than 1, γ

1 is a positive constant equal to or smaller than 1, a linear prediction coefficient sequence which is obtained by linear prediction analysis of audio signals in a predetermined time segment is represented as a[1], a[2], . . . , a[p], and ω

[1], ω

[2], . . . , ω

[p] are a frequency domain parameter sequence derived from the linear prediction coefficient sequence a[1], a[2], . . . , a[p],

a parameter sequence converting unit that determines a converted frequency domain parameter sequence ˜

ω

[1], ˜

ω

[2], . . . , ˜

ω

[p] using the frequency domain parameter sequence ω

[1], ω

[2], . . . , ω

[p] as input, wherein

the parameter sequence converting unit determines a value of each converted frequency domain parameter ˜

ω

[i] (i=1, 2, . . . , p) in the converted frequency domain parameter sequence ˜

ω

[1], ˜

ω

[2], . . . , ˜

ω

[p] through linear transformation which is based on a relationship of values between ω

[i] and one or more frequency domain parameters adjacent to ω

[i], and

each ω

[1] (i=1, 2, . . . , p) in the frequency domain parameter sequence ω

[1], ω

[2], . . . , ω

[p] is a frequency domain parameter equivalent to a<sub>γ

1</sub>[1], a<sub>γ

1</sub>[2], . . . , a<sub>γ

1</sub>[p], or a quantized value of said frequency domain parameter, where a<sub>γ

1</sub>[i]=a[i]×

(γ

1)ⁱ.

22. A encoding apparatus including the units of the frequency domain parameter sequence generating apparatus according to any one of claims 15 to 21, the encoding apparatus comprising:

where γ

is a adjustment factor which is a positive constant equal to or smaller than 1,

a linear prediction coefficient adjusting unit that generates a adjusted linear prediction coefficient sequence a_γ

[1], a_γ

[2], . . . , a_γ

[p] by adjusting the linear prediction coefficient sequence a[1], a[2], . . . , a[p] using the adjustment factor γ

;

a adjusted LSP generating unit that generates a adjusted LSP parameter sequence θ

_γ

[1], θ

_γ

[2], . . . , θ

_γ

[p] using the adjusted linear prediction coefficient sequence a_γ

[1], a_γ

[2], . . . , a_γ

[p];

a adjusted LSP encoding unit that encodes the adjusted LSP parameter sequence θ

_γ

[1], θ

_γ

[2], . . . , θ

_γ

[p] to generate adjusted LSP codes and a adjusted quantized LSP parameter sequence ̂

θ

_γ

[1], ̂

θ

_γ

[2], . . . , ̂

θ

_γ

[p] corresponding to the adjusted LSP codes;

an LSP linear transformation unit that, with the frequency domain parameter sequence ω

[1], ω

[2], . . . , ω

[p] being the adjusted quantized LSP parameter sequence ̂

θ

_γ

[1], ̂

θ

_γ

[2], . . . , ̂

θ

_γ

[p], and γ

1=γ and

γ

2=1, executes the parameter sequence converting unit to thereby generate the converted frequency domain parameter sequence ˜

ω

[1], ˜

ω

[2], . . . , ˜

ω

[p] as an approximate quantized LSP parameter sequence ̂

_app[1], ̂

θ

_app[2], . . . , ̂

θ

_app[p];

a quantized linear prediction coefficient sequence generating unit that generates a adjusted quantized linear prediction coefficient sequence ̂

a_γ

[1], ̂

a_γ

[2], . . . , ̂

a_γ

[p] by converting the adjusted quantized LSP parameter sequence ̂

θ

_γ

[1], ̂

θ

_γ

[2], . . . , ̂

θ

_γ

[p] into linear prediction coefficients;

a quantized smoothed power spectral envelope series calculating unit that calculates a quantized smoothed power spectral envelope series ̂

W_γ

[1], ̂

W_γ

[2], . . . , ̂

W_γ

[N] which is a series in frequency domain corresponding to the adjusted quantized linear prediction coefficient sequence ̂

a_γ

[1], ̂

_γ

[2], . . . , ̂

a_γ

[p];

a frequency domain encoding unit that generates frequency domain signal codes by encoding a frequency domain sample sequence X[1], X[2], X[N] corresponding to the audio signals using the quantized smoothed power spectral envelope series ̂

W_γ

[1], ̂

W_γ

[2], . . . , ̂

W_γ

[N];

an LSP generating unit that generates an LSP parameter sequence θ

[1], θ

[2], . . . , θ

[p] using the linear prediction coefficient sequence a[1], a[2], . . . , a[p];

an LSP encoding unit that encodes the LSP parameter sequence θ

[1], θ

[2], . . . , θ

[p] to generate LSP codes and a quantized LSP parameter sequence ̂

θ

[1], ̂

θ

[2], . . . , ̂

θ

[p] corresponding to the LSP codes; and

a time domain encoding unit that encodes the audio signals to generate time domain signal codes using either a quantized LSP parameter sequence obtained in the LSP encoding unit for a preceding time segment or an approximate quantized LSP parameter sequence obtained in the LSP linear transformation unit for the preceding time segment, and the quantized LSP parameter sequence for the predetermined time segment.

23. A encoding apparatus including the units of the frequency domain parameter sequence generating apparatus according to any one of claims 15 to 21, the encoding apparatus comprising:

where γ

is a adjustment factor which is a positive constant equal to or smaller than 1,

a linear prediction coefficient adjusting unit that generates a adjusted linear prediction coefficient sequence a_γ

[1], a_γ

[2], a_γ

[p] by adjusting the linear prediction coefficient sequence a[1], a[2], . . . , a[p] using the adjustment factor γ

;

a adjusted LSP generating unit that generates a adjusted LSP parameter sequence θ

_γ

[1], θ

_γ

[2], θ

_γ

[p] using the adjusted linear prediction coefficient sequence a_γ

[1], a_γ

[2], . . . , a_γ

[p];

a adjusted LSP encoding unit that encodes the adjusted LSP parameter sequence θ

_γ

[1], θ

_γ

[2], . . . , θ

_γ

[p] to generate adjusted LSP codes and a adjusted quantized LSP parameter sequence ̂

θ

_γ

[1], ̂

θ

_γ

[2], . . . , ̂

θ

_γ

[p] which is determined by quantization of values in the adjusted LSP parameter sequence corresponding to the adjusted LSP codes;

an LSP linear transformation unit that, with the frequency domain parameter sequence ω

[1], ω

[2], . . . , ω

[p] being the adjusted quantized LSP parameter sequence ̂

θ

_γ

[1], ̂

θ

_γ

[2], . . . , ̂

θ

_γ

[p], and γ

1=γ and

γ

2=1, executes the parameter sequence converting unit to thereby generate the converted frequency domain parameter sequence ˜

ω

[1], ˜

ω

[2], . . . , ˜

ω

[p] as an approximate quantized LSP parameter sequence ̂

θ

_app[1], ̂

θ

_app[2], . . . , ̂

θ

_app[p];

a quantized smoothed power spectral envelope series calculating unit that calculates a quantized smoothed power spectral envelope series ̂

W_γ

[1], ̂

W_γ

[2], . . . , ̂

W_γ

[N] based on the adjusted quantized LSP parameter sequence ̂

θ

_γ

[1], ̂

θ

_γ

[2], . . . , ̂

θ

_γ

[p];

a frequency domain encoding unit that generates frequency domain signal codes by encoding a frequency domain sample sequence X[1], X[2], X[N] corresponding to the audio signals using the quantized smoothed power spectral envelope series ̂

W_γ

[1], ̂

W_γ

[2], . . . , ̂

W_γ

[N];

an LSP generating unit that generates an LSP parameter sequence θ

[1], θ

[2], . . . , θ

[p] using the linear prediction coefficient sequence a[1], a[2], . . . , a[p];

an LSP encoding unit that encodes the LSP parameter sequence θ

[1], θ

[2], . . . , θ

[p] to generate LSP codes and a quantized LSP parameter sequence ̂

θ

[1], ̂

θ

[2], . . . , ̂

θ

[p] corresponding to the LSP codes; and

a time domain encoding unit that encodes the audio signals to generate time domain signal codes using either a quantized LSP parameter sequence obtained in the LSP encoding unit for a preceding time segment or an approximate quantized LSP parameter sequence obtained in the LSP linear transformation unit for the preceding time segment, and the quantized LSP parameter sequence for the predetermined time segment.

24. A decoding apparatus including the units of the frequency domain parameter sequence generating apparatus according to any one of claims 15 to 21, the decoding apparatus comprising:

a adjusted LSP code decoding unit that decodes input adjusted LSP codes to obtain a decoded adjusted LSP parameter sequence ̂

θ

_γ

[1], ̂

θ

_γ

[2], . . . , ̂

θ

_γ

[p];

a decoded LSP linear transformation unit that, with the frequency domain parameter sequence ω

[1], ω

[2], . . . , ω

[p] being the decoded adjusted LSP parameter sequence ̂

θ

_γ

[1], ̂

θ

_γ

[2], . . . , ̂

θ

_γ

[p], and γ

1=γ and

γ

2==1, executes the parameter sequence converting unit to thereby generate the converted frequency domain parameter sequence ˜

ω

[1], ˜

ω

[2], . . . , ˜

ω

[p] as a decoded approximate LSP parameter sequence ̂

θ

_app[1], ̂

θ

_app[2], . . . , ̂

θ

_app[p];

a decoded linear prediction coefficient sequence generating unit that generates a decoded adjusted linear prediction coefficient sequence ̂

a_γ

[1], ̂

a_γ

[2], . . . , ̂

a_γ

[p] by converting the decoded adjusted LSP parameter sequence ̂

θ

_γ

[1], ̂

θ

_γ

[2], . . . , ̂

θ

_γ

[p] into linear prediction coefficients;

a decoded smoothed power spectral envelope series calculating unit that calculates a decoded smoothed power spectral envelope series ̂

W_γ

[1], ̂

W_γ

[2], . . . , ̂

W_γ

[N] which is a series in frequency domain corresponding to the decoded adjusted linear prediction coefficient sequence ̂

a_γ

[1], ̂

a_γ

[2], . . . , ̂

a_γ

[p];

a frequency domain decoding unit that generates decoded sound signals using a frequency domain signal sequence resulting from decoding of input frequency domain signal codes and the decoded smoothed power spectral envelope series ̂

W_γ

[1], ̂

W_γ

[2], . . . , ̂

W_γ

[N];

an LSP code decoding unit that decodes input LSP codes to obtain a decoded LSP parameter sequence ̂

θ

[1], ̂

θ

[2], . . . , ̂

θ

[p]; and

a time domain decoding unit that decodes input time domain signal codes, and generates decoded sound signals by synthesizing the time domain signal codes using either the decoded LSP parameter sequence obtained by the LSP code decoding unit for the preceding time segment or the decoded approximate LSP parameter sequence obtained in the decoded LSP linear transformation unit for the preceding time segment, and the decoded LSP parameter sequence for the predetermined time segment.

25. A decoding apparatus including the units of the frequency domain parameter sequence generating apparatus according to any one of claims 15 to 21, the decoding apparatus comprising:

a adjusted LSP code decoding unit that decodes input adjusted LSP codes to obtain a decoded adjusted LSP parameter sequence ̂

θ

_γ

[1], ̂

θ

_γ

[2], . . . , ̂

θ

_γ

[p];

a decoded LSP linear transformation unit that, with the frequency domain parameter sequence ω

[1], θ

[2], . . . , ω

[p] being the decoded adjusted LSP parameter sequence ̂

θ

_γ

[1], ̂

θ

_γ

[2], . . . , ̂

θ

_γ

[p], and γ

1=γ and

γ

2=1, executes the parameter sequence converting unit to thereby generate the converted frequency domain parameter sequence ˜

ω

[1], ˜

ω

[2], . . . , ˜

ω

[p] as a decoded approximate LSP parameter sequence ̂

θ

_app[1], ̂

θ

_app[2], . . . , ̂

θ

_app[p];

a decoded smoothed power spectral envelope series calculating unit that calculates a decoded smoothed power spectral envelope series ̂

W_γ

[1], ̂

W_γ

[2], . . . ̂

W_γ

[N] based on the decoded adjusted LSP parameter sequence ̂

θ

_γ

[1], ̂

θ

₁[2], . . . , ̂

θ

_γ

[p];

a frequency domain decoding unit that generates decoded sound signals using the frequency domain signal sequence resulting from decoding of input frequency domain signal codes and the decoded smoothed power spectral envelope series ̂

W_γ

[1], ̂

W_γ

[2], . . . , ̂

W_γ

[N];

an LSP code decoding unit that decodes input LSP codes to obtain a decoded LSP parameter sequence ̂

θ

[1], ̂

θ

[2], . . . , ̂

θ

[p]; and

a time domain decoding unit that decodes input time domain signal codes, and generates decoded sound signals by synthesizing the time domain signal codes using either the decoded LSP parameter sequence obtained in the LSP code decoding unit for the preceding time segment or the decoded approximate LSP parameter sequence obtained in the decoded LSP linear transformation unit for the preceding time segment, and the decoded LSP parameter sequence for the predetermined time segment.

16. A frequency domain parameter sequence generating apparatus comprising:

where p is an integer equal to or greater than 1, and a linear prediction coefficient sequence obtained by linear prediction analysis of audio signals in a predetermined time segment is represented as a[1], a[2], . . . , a[p];

ω

[1], ω

[2], . . . , ω

[p] is one of

an LSP parameter sequence derived from the linear prediction coefficient sequence a[1], a[2], . . . , a[p],

an ISP parameter sequence derived from the linear prediction coefficient sequence a[1], a[2], . . . , a[p],

an LSF parameter sequence derived from the linear prediction coefficient sequence a[1], a[2], . . . , a[p],

an ISF parameter sequence derived from the linear prediction coefficient sequence a[1], a[2], . . . , a[p], and

a frequency domain parameter sequence which is derived from the linear prediction coefficient sequence a[1], a[2], . . . , a[p] and in which all of ω

[1], ω

[2], . . . , ω

[p−

1] are present from 0 to π and

, when all of linear prediction coefficients contained in the linear prediction coefficient sequence are 0, ω

[1], ω

[2], . . . , ω

[p−

1] are present from 0 to π

at equal intervals; and

each γ

1 and γ

2 is a positive constant equal to or smaller than 1, and K is a predetermined p×

p band matrix in which diagonal elements and elements that neighbor the diagonal elements in row direction have non-zero values,

a parameter sequence converting unit that generates a converted frequency domain parameter sequence ˜

ω

[1], ˜

ω

[2], . . . , ˜

ω

[p] defined by a following formula.

17. The frequency domain parameter sequence generating apparatus according to claim 16, wherein

the band matrix K has positive values in the diagonal elements and negative values in elements that neighbor the diagonal elements in row direction.

19. The frequency domain parameter sequence generating apparatus according to claim 16, wherein

the band matrix K has values greater than or equal to 0 in diagonal elements and values smaller than or equal to 0 in elements that neighbor the diagonal elements in row direction.

18. A frequency domain parameter sequence generating apparatus comprising:

where p is an integer equal to or greater than 1, a linear prediction coefficient sequence which is obtained by linear prediction analysis of audio signals in a predetermined time segment is represented as a[1], a[2], . . . , a[p], and ω

[1], ω

[2], . . . , ω

[p] are a frequency domain parameter sequence which is derived from the linear prediction coefficient sequence a[1], a[2], . . . , a[p] and in which all of ω

[1], ω

[2], . . . , ω

[p−

1] are present from 0 to π and

, when all of linear prediction coefficients contained in the linear prediction coefficient sequence are 0, ω

[1], ω

[2], . . . , ω

[p−

1] are present from 0 to π

at equal intervals, and

where each γ

1 and γ

2 is a positive constant equal to or smaller than 1, and K is a predetermined p×

p band matrix in which diagonal elements and elements that neighbor the diagonal elements in row direction have non-zero values,

a parameter sequence converting unit that determines a converted frequency domain parameter sequence ˜

ω

[1], ˜

ω

[2], . . . , ˜

ω

[p] using the frequency domain parameter sequence ω

[1], ω

[2], . . . , ω

[p] as input, wherein

the parameter sequence converting unit determines each ˜

ω

[i] (i=1, 2, . . . , p) in the converted frequency domain parameter sequence ˜

ω

[1], ˜

ω

[2], . . . , ˜

ω

[p] such that

when ω

[i] is closer to ω

[i+1] relative to a midpoint between ω

[i+1] and ω

[i−

1], then ˜

ω

[i] is determined so that ˜

ω

[i] will be closer to ˜

ω

[i+1] relative to the midpoint between ˜

ω

[i+1] and ˜

ω

[i−

1] and that a value of ˜

ω

[i+1]−

˜

ω

[i] will be smaller than ω

[i+1]−

ω

[i], and

when ω

[i] is closer to ω

[i−

1] relative to the midpoint between ω

[i+1] and ω

[i−

1], then ˜

ω

[i] is determined so that ˜

ω

[i] will be closer to ˜

ω

[i−

1] relative to the midpoint between ˜

ω

[i+1] and ˜

ω

[i−

1] and that the value of ˜

ω

[i]−

˜

ω

[i−

1] will be smaller than ω

[i]−

ω

[i−

1], and

a converted frequency domain parameter sequence −

ω

[1], ˜

ω

[2], . . . , ˜

ω

[p] defined by

20. A frequency domain parameter sequence generating apparatus comprising:

where p is an integer equal to or greater than 1, γ

1 is a positive constant equal to or smaller than 1, a linear prediction coefficient sequence which is obtained by linear prediction analysis of audio signals in a predetermined time segment is represented as a[1], a[2], . . . , a[p], and ω

[1], θ

[2], . . . , ω

[p] are a frequency domain parameter sequence derived from the linear prediction coefficient sequence a[1], a[2], . . . , a[p],

a parameter sequence converting unit that determines converted frequency domain parameter sequence ˜

ω

[1], ˜

ω

[2], . . . , ˜

ω

[p] using the frequency domain parameter sequence ω

[1], ω

[2], . . . , ω

[p] as input, wherein

the parameter sequence converting unit determines each ω

[i] (i=1, 2, . . . , p) in the converted frequency domain parameter sequence ˜

ω

[1], ˜

ω

[2], . . . , ˜

ω

[p] such that

when ω

[i] is closer to ω

[i+l] relative to a midpoint between ω

[i+l] and ω

[i−

1], then ˜

ω

[i] is determined so that ˜

ω

[i] will be closer to ˜

ω

[i+1] relative to the midpoint between ˜

ω

[i+1] and ˜

ω

[i−

1] and that a value of ˜

ω

[i+1]−

˜

ω

[i] will be smaller than ω

[i+1]−

ω

[i], and

when ω

[i] is closer to ω

[i−

1] relative to the midpoint between ω

[i+1] and ω

[i−

1], then ˜

ω

[i] is determined so that ˜

ω

[i] will be closer to ˜

ω

[i−

1] relative to the midpoint between ˜

ω

[i+1] and ˜

ω

[i−

1] and that the value of ˜

ω

[i]−

˜

ω

[i−

1] will be smaller than ω

[i]−

ω

[i−

1], and

each ω

[i] (i=1, 2, . . . , p) in the frequency domain parameter sequence ω

[1], ω

[2], . . . , ω

[p] is a frequency domain parameter equivalent to a<sub>γ

1</sub>[1], a<sub>γ

1</sub>[2], . . . , a<sub>γ

1</sub>[p], or a quantized value of said frequency domain parameter, where a<sub>γ

1</sub>[i]=a[i]×

(γ

1)ⁱ.

21. A frequency domain parameter sequence generating apparatus comprising:

where p is an integer equal to or greater than 1, γ

1 is a positive constant equal to or smaller than 1, a linear prediction coefficient sequence which is obtained by linear prediction analysis of audio signals in a predetermined time segment is represented as a[1], a[2], . . . , a[p], and ω

[1], ω

[2], . . . , ω

[p] are a frequency domain parameter sequence derived from the linear prediction coefficient sequence a[1], a[2], . . . , a[p],

a parameter sequence converting unit that determines a converted frequency domain parameter sequence ˜

ω

[1], ˜

ω

[2], . . . , ˜

ω

[p] using the frequency domain parameter sequence ω

[1], ω

[2], . . . , ω

[p] as input, wherein

the parameter sequence converting unit determines each ˜

ω

[i] (i=1, 2, . . . , p) in the converted frequency domain parameter sequence ˜

ω

[1], ˜

ω

[2], . . . , ˜

ω

[p] such that

when ω

[i] is closer to ω

[i+1] relative to the midpoint between ω

[i+1] and ω

[i−

1], then ˜

ω

[i] is determined so that ˜

ω

[i] will be closer to ˜

ω

[i+1] relative to the midpoint between ˜

ω

[i+1] and ω

[i−

1] and that a value of ω

[i+1]−

˜

ω

[i] will be greater than ω

[i+1]−

˜

ω

[i], and

when ω

[i] is closer to ω

[i−

1] relative to the midpoint between ω

[i+1] and ω

[i−

1], then ˜

ω

[i] is determined so that ˜

ω

[i] will be closer to ˜

ω

[i−

1] relative to the midpoint between ˜

ω

[i+1] and ˜

ω

[i−

1] and that the value of ˜

ω

[i]−

˜

ω

[i−

1] will be greater than ω

[i]−

ω

[i−

1], and

each ω

[i] (i=1, 2, . . . , p) in the frequency domain parameter sequence ω

[1], ω

[2], . . . , ω

[p] is a frequency domain parameter equivalent to a<sub>γ

1</sub>[1], a<sub>γ

1</sub>[2], . . . , a<sub>γ

1</sub>[p], or a quantized value of said frequency domain parameter, where a<sub>γ

1</sub>[i]=a[i]×

(γ

1)ⁱ.

27-28. -28. (canceled)

30-31. -31. (canceled)