Speech post-processing using MDCT coefficients

• US 8,095,360 B2
• Filed: 07/17/2009
• Issued: 01/10/2012
• Est. Priority Date: 03/20/2006
• Status: Active Grant

• Current Assignee: Nytell Software LLC (Intellectual Ventures LLC)
• Original Assignee: Mindspeed Technologies Inc. (MACOM Technology Solutions Holdings, Inc.)
• Inventors: Gao, Yang
• Primary Examiner(s): Dorvil, Richemond
• Assistant Examiner(s): Borsetti, Greg
• Application Number:
  US12/460,428
• Publication Number:
  US 20090287478A1
• Time in Patent Office: 907 Days
• Field of Search: 704/200, 704/205, 704/E19.017, 704/222, 704/E19.045, 704/E19.047
• US Class Current: 704/205
• CPC Class Codes: G10L 19/0212 using orthogonal transformation
• CPC Class Codes: G10L 19/26 Pre-filtering or post-filtering
• CPC Class Codes: G10L 25/27 characterised by the analysis technique

Abstract

There is provided a method of post-processing a speech signal. The method comprises applying a time-domain post-processing to the speech signal, using LPC coefficients, for a low-band frequency range and applying a frequency-domain post-processing to the speech signal, using MDCT coefficients, for the high-band frequency range. Applying the frequency-domain post-processing includes decoding an encoded speech signal to obtain MDCT coefficients representative of the speech signal divided into a plurality of sub-bands, generating an envelope for each sub-band of the plurality of sub-bands as an average magnitude of the MDCT coefficients of the sub-band, generating an envelope modification factor for each sub-band of the plurality of sub-band using the MDCT coefficients of the sub-band, modifying the envelope by the envelope modification factor for each sub-band of the plurality of sub-bands to provide a modified envelope, and generating the post-processed speech signal using the modified envelope.

Claims

1. A method of post-processing a speech signal having a high-band frequency range and a low-band frequency range to generate a post-processed speech signal, the method comprising:

applying a time-domain post-processing to the speech signal, using LPC (Linear Prediction Coding) coefficients, for the low-band frequency range of the speech signal;

applying a frequency-domain post-processing to the speech signal, using MDCT (Modified Discrete Cosine Transform) coefficients, for the high-band frequency range of the speech signal;

wherein applying the frequency-domain post-processing includes;

decoding an encoded speech signal to obtain MDCT coefficients representative of the speech signal divided into a plurality of sub-bands;

generating an envelope for each sub-band of the plurality of sub-bands as an average magnitude of the MDCT coefficients of the sub-band;

generating an envelope modification factor for each sub-band of the plurality of sub-bands using the MDCT coefficients of the sub-band;

determining a gain based on the envelope and the envelope modification factor of the sub-bands;

generating a fine structure modification factor for each MDCT coefficient in each sub-band of the plurality of sub-band using the MDCT coefficients of the sub-band;

modifying the MDCT coefficients in each sub-band by multiplying by the gain, the envelope modification factor of the sub-band and the fine structure modification factor of the MDCT coefficient of the sub-band to provide post-processed MDCT coefficients;

generating the post-processed speech signal using the post-processed MDCT coefficients; and

converting the post-processed speech signal from a digital form into an analog form using an digital-to-analog converter.

2. The method of claim 1, wherein the envelope is defined by:

3. The method of claim 1, wherein each sub-band of the plurality of sub-bands includes at least one harmonic peak.

4. The method of claim 1, wherein the generating of the envelope modification factor further uses the envelope.

5. The method of claim 1, wherein the generating of the envelope modification factor further uses the maximum value of the envelope of each the sub-band of the plurality of sub-bands.

6. A speech post-processor for post-processing a speech signal having a high-band frequency range and a low-band frequency range to generate a post-processed speech signal, the speech post-processor comprising:

software and circuitry for;

applying a time-domain post-processing to the speech signal, using LPC (Linear Prediction Coding) coefficients, for the low-band frequency range of the speech signal;

applying a frequency-domain post-processing to the speech signal, using MDCT (Modified Discrete Cosine Transform) coefficients, for the high-band frequency range of the speech signal;

wherein applying the frequency-domain post-processing includes;

decoding an encoded speech signal to obtain MDCT coefficients representative of the speech signal divided into a plurality of sub-bands;

generating an envelope for each sub-band of the plurality of sub-bands as an average magnitude of the MDCT coefficients of the sub-band;

generating an envelope modification factor for each sub-band of the plurality of sub-bands using the MDCT coefficients of the sub-band;

determining a gain based on the envelope and the envelope modification factor of the sub-bands;

generating a fine structure modification factor for each MDCT coefficient in each sub-band of the plurality of sub-band using the MDCT coefficients of the sub-band;

modifying the MDCT coefficients in each sub-band by multiplying by the gain, the envelope modification factor of the sub-band and the fine structure modification factor of the MDCT coefficient of the sub-band to provide post-processed MDCT coefficients;

generating the post-processed speech signal using the post-processed MDCT coefficients; and

converting the post-processed speech signal from a digital form into an analog form using an digital-to-analog converter.

7. The speech post-processor of claim 6, wherein the envelope is defined by:

8. The speech post-processor of claim 6, wherein each sub-band of the plurality of sub-bands includes at least one harmonic peak.

9. The speech post-processor of claim 6, wherein the generating of the envelope modification factor further uses the envelope.

10. The speech post-processor of claim 6, wherein the generating of the envelope modification factor further uses the maximum value of the envelope of each the sub-band of the plurality of sub-bands.