Adaptive postfiltering methods and systems for decoding speech

• US 8,032,363 B2
• Filed: 08/09/2002
• Issued: 10/04/2011
• Est. Priority Date: 10/03/2001
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Lee, Chris C, Chen, Juin-Hwey, Thyssen, Jes
• Primary Examiner(s): Wozniak; James S.
• Assistant Examiner(s): Serrou; Abdelali
• Application Number:
  US10/215,048
• Publication Number:
  US 20030088405A1
• Time in Patent Office: 3,343 Days
• Field of Search: 704/216, 704/226, 704/225, 704/208, 704/219, 704/223, 704/220, 704/232, 704/201, 704500-504
• US Class Current: 704/225
• CPC Class Codes: G10L 19/26 Pre-filtering or post-filtering

Abstract

A method of processing a decoded speech (DS) signal including successive DS frames, each DS frame including DS samples. The method comprises: adaptively filtering the DS signal to produce a filtered signal; gain-scaling the filtered signal with an adaptive gain updated once a DS frame, thereby producing a gain-scaled signal; and performing a smoothing operation to smooth possible waveform discontinuities in the gain-scaled signal.

Claims

1. A method of processing a decoded speech (DS) signal having successive DS frames, the method comprising:

(a) adaptively filtering the DS signal to produce a filtered signal;

(b) gain-scaling the filtered signal with an adaptive gain updated once a DS frame in the successive DS frames, thereby producing a gain-scaled signal, wherein the gain-scaled signal includes successive gain-scaled signal frames corresponding to the successive DS frames; and

(c) performing a smoothing operation on the gain-scaled signal to smooth possible waveform discontinuities in the gain-scaled signal between adjacent gain-scaled signal frames, wherein each DS frame, in the successive DS frames, includes a plurality of DS samples; and

wherein the adaptive gain is calculated based on a ratio of a gain of the DS signal to a gain of the filtered signal.

2. The method of claim 1, wherein said filtering step (a) comprises at least one of long-term filtering and short-term filtering.

3. The method of claim 2, wherein said filtering step (a) further comprises at least one of

long-term filtering followed by short-term filtering, and

short-term filtering followed by long-term filtering.

4. The method of claim 1, wherein step (c) further comprises performing an overlap-add operation based on the adjacent gain-scaled signal frames.

5. The method of claim 1, wherein:

step (a) includes filtering a beginning portion of a current DS frame using a current set of filter coefficients, to produce a first filtered frame portion;

step (b) includes gain-scaling the first filtered frame portion using a current gain, to produce a first gain-scaled frame portion; and

the smoothing operation of step (c) includes

filtering and gain-scaling the beginning portion of the current DS frame using a previous set of filter coefficients and a previous gain, respectively, to produce a second gain-scaled portion, and

modifying the first gain-scaled frame portion with the second gain-scaled frame portion so as to smooth a possible waveform discontinuity.

6. The method of claim 1, wherein said filtering step (a) comprises short-term filtering using one of an all-zero filter, an all-pole filter, and a pole-zero filter.

7. The method of claim 1, wherein said filtering step (a) comprises long-term filtering using one of an all-zero filter, an all-pole filter, and a pole-zero filter.

8. The method of claim 1, wherein said filtering step (a) comprises filtering without gain-scaling.

9. An apparatus for processing a decoded speech (DS) signal having successive DS frames, the apparatus comprising:

an adaptive filter device configured to adaptively filter the DS signal to produce a filtered signal;

a gain scaler device configured to gain-scale the filtered signal with an adaptive gain updated once a DS frame in the successive DS frames, to produce a gain-scaled signal, wherein the gain-scaled signal includes successive gain-scaled signal frames corresponding to the successive DS frames; and

a module configured to perform a smoothing operation on the gain-scaled signal to smooth possible waveform discontinuities in the gain-scaled signal between adjacent gain-scaled signal frames, wherein each DS frame, in the successive DS frames, includes a plurality of DS samples; and

wherein the adaptive gain is calculated based on a ratio of a gain of the DS signal to a gain of the filtered signal.

10. The apparatus of claim 9, wherein the adaptive filter device comprises at least one of a long-term filter and a short-term filter.

11. The apparatus of claim 10, wherein the adaptive filter device further comprises at least one of a long-term filter followed by short-term filter, and

short-term filter followed by lone-term filter.

12. The apparatus of claim 9, wherein the smoothing operation further comprises performing an overlap-add operation based on the adjacent gain-scaled signal frames.

13. The apparatus of claim 9, wherein:

the adaptive filter device is configured to filter a beginning portion of a current DS frame using a current set of filter coefficients, to produce a first filtered frame portion;

the gain scaler device is configured to gain-scale the first filtered frame portion using a current gain, to produce a first gain-scaled frame portion; and

the module includes means for performing the smoothing operation, the smoothing means including

means for filtering and gain-scaling the beginning portion of the current DS frame using a previous set of filter coefficients and a previous gain, respectively, to produce a second gain-scaled portion, and

means for modifying the first gain-scaled frame portion with the second gain-Scaled frame portion so as to smooth a possible waveform discontinuity.

14. The apparatus of claim 9, wherein the adaptive filter device comprises a short-term filter having one of ah all-zero filter response, an all-pole filter response, and a pole-zero filter response.

15. The apparatus of claim 9, wherein the adaptive filter device comprises a long-term filter having one of an all-zero filter response, an all-pole filter response, and a pole-zero filter response.

16. The apparatus of claim 9, wherein the adaptive filter device is configured to perform filtering without gain-scaling.