SPEECH ENCODING APPARATUS AND SPEECH ENCODING METHOD

• US 20090157413A1
• Filed: 09/29/2006
• Published: 06/18/2009
• Est. Priority Date: 09/30/2005
• Status: Active Grant

• Current Assignee: III Holdings 12, LLC (Intellectual Ventures LLC)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Oshikiri, Masahiro
• Granted Patent: US 8,396,717 B2
• Time in Patent Office: Days
• US Class Current: 704/501
• CPC Class Codes: G10L 19/04 using predictive techniques
• CPC Class Codes: G10L 21/02 Speech enhancement, e.g. noise reduction or echo cancellation reducing echo effects in line transmission systems H04B3/20; echo suppression in hands-free telephones H04M9/08
• CPC Class Codes: G10L 21/038 using band spreading techniques

Abstract

There is provided an audio encoding device capable of maintaining continuity of spectrum energy and preventing degradation of audio quality even when a spectrum of a low range of an audio signal is copied at a high range a plurality of times. The audio encoding device (100) includes: an LPC quantization unit (102) for quantizing an LPC coefficient; an LPC decoding unit (103) for decoding the quantized LPC coefficient; an inverse filter unit (104) for flattening the spectrum of the input audio signal by the inverse filter configured by using the decoding LPC coefficient; a frequency region conversion unit (105) for frequency-analyzing the flattened spectrum; a first layer encoding unit (106) for encoding the low range of the flattened spectrum to generate first layer encoded data; a first layer decoding unit (107) for decoding the first layer encoded data to generate a first layer decoded spectrum, and a second layer encoding unit (108) for encoding.

Claims

1. A speech encoding apparatus comprising:

a first encoding section that encodes a low band spectrum comprising a lower band than a threshold frequency of a speech signal;

a flattening section that flattens the low band spectrum using an inverse filter with inverse characteristics of a spectral envelope of the speech signal; and

a second encoding section that encodes a high band spectrum comprising a higher band than the threshold frequency of the speech signal using the flattened low band spectrum.

2. The speech encoding apparatus according to claim 1, wherein the flattening section forms the inverse filter using linear prediction coding coefficients of the speech signal.

3. The speech encoding apparatus according to claim 1, wherein the flattening section changes a degree of flattening according to a degree of resonance of the speech signal.

4. The speech encoding apparatus according to claim 3, wherein, when the degree of resonance is greater, the flattening section sets the degree of flattening lower.

5. The speech encoding apparatus according to claim 1, wherein the second encoding section modifies the flattened low band spectrum and encodes the high band spectrum using the modified low band spectrum.

6. The speech encoding apparatus according to claim 5, wherein the second encoding section modifies the flattened low band spectrum such that a dynamic range of the flattened low band spectrum is adjusted closer to a dynamic range of the high band spectrum.

7. The speech encoding apparatus according to claim 6, wherein the second encoding section modifies the flattened low band spectrum using an encoding candidate that decreases a dynamic range preferentially over an encoding candidate that increases the dynamic range, among a plurality of encoding candidates.

8. The speech encoding apparatus according to claim 7, wherein the second encoding section carries out correction such that an encoding candidate search target value becomes smaller, and, based on the corrected target value, searches for an encoding candidate used to modify the flattened low band spectrum among the plurality of encoding candidates.

9. The speech encoding apparatus according to claim 5, wherein the second encoding section estimates the high band spectrum from the modified low band spectrum, modifies the estimated high band spectrum and encodes the high band spectrum of the speech signal by using the modified high band spectrum.

10. The speech encoding apparatus according to claim 1, wherein the second encoding section estimates the high band spectrum from the flattened low band spectrum, modifies the estimated high band spectrum and encodes the high band spectrum of the speech signal by using the modified high band spectrum.

11. A radio communication mobile station apparatus comprising the speech encoding apparatus according to claim 1.

12. A radio communication base station apparatus comprising the speech encoding apparatus according to claim 1.

13. A speech encoding method comprising:

A first encoding step of encoding a low spectrum band comprising a lower band than a threshold frequency of a speech signal;

A flattening step of flattening the low band spectrum using an inverse filter with inverse characteristics to a spectral envelope of the speech signal; and

A second encoding step of encoding a high band spectrum comprising a higher band than the threshold frequency of the speech signal using the flattened low band spectrum.