Linear prediction coefficient conversion device and linear prediction coefficient conversion method

• US 10,163,448 B2
• Filed: 04/16/2015
• Issued: 12/25/2018
• Est. Priority Date: 04/25/2014
• Status: Active Grant

• Current Assignee: NTT Docomo Incorporated (Nippon Telegraph and Telephone Corporation)
• Original Assignee: NTT Docomo Incorporated (Nippon Telegraph and Telephone Corporation)
• Inventors: Naka, Nobuhiko, Ruoppila, Vesa
• Primary Examiner(s): Shah, Paras D
• Assistant Examiner(s): Blankenagel, Bryan S
• Application Number:
  US15/306,292
• Publication Number:
  US 20170053655A1
• Time in Patent Office: 1,349 Days
• CPC Class Codes: G10L 19/06 Determination or coding of the spectral characteristics, e.g. of the short-term prediction coefficients
• 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 25/12 the extracted parameters being prediction coefficients

Abstract

The purpose of the present invention is to estimate, with a small amount of computation, a linear prediction synthesis filter after conversion of an internal sampling frequency. A linear prediction coefficient conversion device is a device that converts first linear prediction coefficients calculated at a first sampling frequency to second linear prediction coefficients at a second sampling frequency different from the first sampling frequency, which includes a means for calculating, on the real axis of the unit circle, a power spectrum corresponding to the second linear prediction coefficients at the second sampling frequency based on the first linear prediction coefficients or an equivalent parameter, a means for calculating, on the real axis of the unit circle, autocorrelation coefficients from the power spectrum, and a means for converting the autocorrelation coefficients to the second linear prediction coefficients at the second sampling frequency.

Claims

1. A linear prediction coefficient conversion device comprising circuitry configured to:

determine a first linear prediction synthesis filter at a first sampling frequency, the first linear prediction synthesis filter comprising first linear prediction coefficients associated therewith;

calculate, using line spectrum frequency (LSF) decomposition and Chebyshev polynomials, a power spectrum based on the first linear prediction coefficients;

calculate autocorrelation coefficients from the power spectrum based, at least in part, on a number of frequencies associated with a second sampling frequency, wherein the number of frequencies associated with the second sampling frequency is different than a number of frequencies associated with the first sampling frequency;

generate, based, at least in part, on the autocorrelation coefficients calculated from the power spectrum, a second linear prediction synthesis filter at the second sampling frequency, wherein the second linear prediction synthesis filter comprises second linear prediction coefficients associated therewith; and

encode or decode an audio signal by replacement of the first linear prediction synthesis filter with the second linear prediction synthesis filter.

2. The linear prediction coefficient conversion device according to claim 1, wherein the power spectrum is calculated using the first linear prediction coefficients at points on a real axis of a unit circle corresponding to N1 number of different frequencies at the first sampling frequency (F1), where N1=1+(F1/F2)(N2−

1), and where there are N2 number of different frequencies at the second sampling frequency (F2) (where F1<

F2), and the circuitry is further configured to extrapolate the power spectrum calculated using the first linear prediction coefficients to obtain (N2−

N1) number of power spectrum components.

3. The linear prediction coefficient conversion device according to claim 1, wherein the power spectrum is calculated using the first linear prediction coefficients at points on a real axis of a unit circle corresponding to N1 number of different frequencies at the first sampling frequency (F1), where N1=1+(F1/F2)(N2−

1), and where there are N2 number of different frequencies at the second sampling frequency (F2) (where F1<

F2).

4. The linear prediction coefficient conversion device according to claim 1, wherein the circuity is configured to calculate both the power spectrum and the autocorrelation coefficients on a real axis of a unit circle.

5. The linear prediction coefficient conversion device according to claim 1, wherein the circuitry is configured to determine the second linear prediction coefficients by:

derivation of linear prediction coefficients from the autocorrelation coefficients; and

conversion of the linear prediction coefficients into LSF coefficients.

6. The linear prediction coefficient conversion device according to claim 1, wherein the circuitry is configured to process the audio signal by encoding or decoding a speech signal with the second linear prediction synthesis filter.

7. A linear prediction coefficient conversion

determining a first linear prediction synthesis filter at a first sampling frequency, the first linear prediction synthesis filter comprising first linear prediction coefficients associated therewith;

calculating, using line spectrum frequency (LSF) decomposition and Chebyshev polynomials, a power spectrum based on the first linear prediction coefficients;

calculating autocorrelation coefficients from the power spectrum based, at least in part, on a number of frequencies associated with a second sampling frequency, wherein the number of frequencies associated with the second sampling frequency is different than a number of frequencies associated with the first sampling frequency;

generating a second linear prediction synthesis filter at the second sampling frequency based, at least in part, on the autocorrelation coefficients calculated from the power spectrum, wherein the second linear prediction synthesis filter comprises second linear prediction coefficients are associated therewith; and

encoding or decoding an audio signal in conjunction with replacing the first linear prediction filter with the second linear prediction filter.

8. The linear prediction coefficient conversion method according to claim 7, wherein the power spectrum is calculated using the first linear prediction coefficients at points on a real axis of a unit circle corresponding to N1 number of different frequencies at the first sampling frequency (F1), where N1=1+(F1/F2)(N2−

1), and where there are N2 number of different frequencies at the second sampling frequency (F2) (where F1<

F2), and extrapolating the power spectrum calculated using the first linear prediction coefficients for obtaining (N2−

N1) number of power spectrum components.

9. The linear prediction coefficient conversion method according to claim 7, wherein the power spectrum is calculated using the first linear prediction coefficients at points on a real axis of a unit circle corresponding to N1 number of different frequencies at the first sampling frequency (F1), where N1=1+(F1/F2)(N2−

1), and where there are N2 number of different frequencies at the second sampling frequency is (F2) (where F1<

F2).

10. The linear prediction coefficient conversion method according to claim 7, wherein the power spectrum and the autocorrelation coefficients are both calculated on a real axis of a unit circle.

11. The linear prediction coefficient conversion method according to claim 7, further comprising converting the second linear prediction coefficients into LSF coefficients.

12. The linear prediction coefficient conversion method according to claim 7, wherein processing the audio signal comprises encoding the audio signal using the second linear prediction synthesis filter.

13. The linear prediction coefficient conversion method according to claim 7, wherein processing the audio signal comprises decoding the audio signal using the second linear prediction synthesis filter.