Speech post-processing using MDCT coefficients

• US 20090287478A1
• Filed: 07/17/2009
• Published: 11/19/2009
• 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
• Granted Patent: US 8,095,360 B2
• Time in Patent Office: Days
• US Class Current: 704/204
• 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 speech post-processor for enhancing a speech signal divided into a plurality of sub-bands in frequency domain. The speech post-processor comprises an envelope modification factor generator configured to use frequency domain coefficients representative of an envelope derived from the plurality of sub-bands to generate an envelope modification factor for the envelope derived from the plurality of sub-bands, where the envelope modification factor is generated using FAC=αENV/Max+(1−α), where FAC is the envelope modification factor, ENV is the envelope, Max is the maximum envelope, and a is a value between 0 and 1, where α is a different constant value for each speech coding rate. The speech post-processor further comprises an envelope modifier configured to modify the envelope derived from the plurality of sub-bands by the envelope modification factor corresponding to each of the plurality of sub-bands.

Claims

1-20. -20. (canceled)

21. :

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 modification factor using the MDCT coefficients for each of the plurality of sub-bands;

modifying an envelope, defined by an average magnitude in each of the plurality of sub-bands, using the envelope modification factor corresponding to each of the plurality of sub-bands to provide a modified envelope; and

generating the post-processed speech signal using the modified envelope.

22. :

The method of claim 21, wherein the modifying the envelope includes multiplying the envelope by the envelope modification factor.

23. :

The method of claim 21, wherein the envelope is defined by;

24. :

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 modification factor using the MDCT coefficients for each of the plurality of sub-bands;

modifying an envelope, defined by an average magnitude in each of the plurality of sub-bands, using the envelope modification factor corresponding to each of the plurality of sub-bands to provide a modified envelope; and

generating the post-processed speech signal using the modified envelope.

25. :

The speech post-processor of claim 24, wherein the modifying the envelope includes multiplying the envelope by the envelope modification factor.

26. :

The speech post-processor of claim 24, wherein the envelope is defined by;

27. :

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 modification factor using the MDCT coefficients;

generating a fine structure modification factor using the MDCT coefficients;

determining a gain based on the envelope modification factor and an envelope;

modifying the frequency domain coefficients as a result of multiplying the MDCT coefficients by the gain, the envelope modification factor and the fine structure modification factor to provide post-processed MDCT coefficients; and

generating the post-processed speech signal using the post-processed MDCT coefficients.

28. :

The method of claim 27, wherein the envelope is defined by;

29. :

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 modification factor using the MDCT coefficients;

generating a fine structure modification factor using the MDCT coefficients;

determining a gain based on the envelope modification factor and an envelope;

modifying the frequency domain coefficients as a result of multiplying the MDCT coefficients by the gain, the envelope modification factor and the fine structure modification factor to provide post-processed MDCT coefficients; and

generating the post-processed speech signal using the post-processed MDCT coefficients.

30. :

The speech post-processor of claim 29, wherein the envelope is defined by;