Adaptive postfiltering methods and systems for decoding speech
View Patent ↗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.
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.