Frame erasure concealment for predictive speech coding based on extrapolation of speech waveform

• US 7,590,525 B2
• Filed: 08/19/2002
• Issued: 09/15/2009
• Est. Priority Date: 08/17/2001
• Status: Expired due to Fees

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Chen, Juin-Hwey
• Primary Examiner(s): Vo; Huyen X.
• Application Number:
  US10/222,934
• Publication Number:
  US 20030078769A1
• Time in Patent Office: 2,584 Days
• Field of Search: 704/223, 704/228, 704/219, 704/220, 704/221, 704/222, 704/230, 704500-504, 704/211, 704/207, 704/216, 704/217
• US Class Current: 704/211
• CPC Class Codes: G10L 19/005 Correction of errors induced by the transmission channel, if related to the coding algorithm

Abstract

A method and system are provided for synthesizing a number of corrupted frames output from a decoder including one or more predictive filters. The corrupted frames are representative of one segment of a decoded signal (sq(n)) output from the decoder. The method comprises determining a first preliminary time lag (ppfe1) based upon examining a predetermined number (K) of samples of another segment of the decoded signal and determining a scaling factor (ptfe) associated with the examined number (K) of samples when the first preliminary time lag (ppfe1) is determined. The method also comprises extrapolating one or more replacement frames based upon the first preliminary time lag (ppfe1) and the scaling factor (ptfe).

Claims

1. A method of synthesizing a number of corrupted frames output from a decoder including one or more predictive filters, the corrupted frames being representative of one segment of a decoded signal (sq(n)) output from the decoder, the method comprising:

determining, using at least one processor, a first preliminary time lag (ppfe1) based upon examining a predetermined number (K) of samples of another segment of the decoded signal;

determining, using the at least one processor, a scaling factor (ptfe) associated with the examined number (K) of samples, the scaling factor (ptfe) only being a function of (i) the first preliminary time lag (ppfe1) and (ii) the decoded signal (sq(n)); and

extrapolating, using the at least one processor, a first replacement frame based upon the first preliminary time lag (ppfe1) and the scaling factor (ptfe).

2. The method of claim 1, further comprising updating internal states of the filters based upon the extrapolating.

3. The method of claim 2, wherein the examined number (K) of samples is selected from within a number (N) of stored samples;

wherein correlation values (c(j)) associated with candidate preliminary time lags (j) are determined in accordance with the expression;

4. The method of claim 3, wherein the scaling factor (ptfe) is determined in accordance with the expression:

5. The method of claim 4, further comprising examining the first preliminary lag (ppfe1) when (i) the number of frames includes consecutively corrupted frames and (ii) a second of the number of consecutively corrupted frames is received;

wherein the other segment includes a last received good frame immediately preceding a first of the number of consecutively corrupted frames.

6. The method of claim 5, wherein the examining includes comparing the first preliminary time lag (ppfe1) with other time lags respectively associated with other received good frames, the other good frames immediately preceding the last received good frame.

7. The method of claim 5, further comprising modifying the first preliminary time lag (ppfe1) based upon the comparing if a change between the first preliminary time lag (ppfe1) and the other time lags exceeds a predetermined amount.

8. The method of claim 7, wherein the predetermined amount is within about five percent and is based upon a change between the first preliminary time lag (ppfe1) and each of the other time lags.

9. The method of claim 8, wherein the other received good frames include up to four frames.

10. The method of claim 9, wherein the modifying further includes (i) determining a pitch change per frame, (ii) rounding the determined pitch change per frame to a nearest integer value, (iii) adding the integer value to the first preliminary time lag (ppfe1) to produce an adjusted first preliminary time lag (ppfe1).

11. The method of claim 10, further comprising performing a first waveform extrapolation to extrapolate the at least one of the subsequent replacement frames based upon the adjusted first preliminary time lag (ppfe1) and the scaling factor (ptfe).

12. The method of claim 1, further comprising determining a periodic extrapolation flag (pwef) for the examined predetermined number (K) of samples.

13. The method of claim 12, wherein the determining the extrapolation flag (pwef) includes calculating (i) a normalized logarithmic signal gain (nlg), (ii) a pitch prediction gain (ppg), and a (iii) first normalized autocorrelation coefficient(ρ

₁), the normalized logarithmic signal gain, the pitch prediction gain, and the normalized autocorrelation coefficient being associated with the decoded signal.

14. The method of claim 13, wherein the determining of the extrapolation flag (pwef) further includes (i) calculating a weighted sum of the normalized logarithmic signal gain, the pitch prediction gain, and the normalized autocorrelation coefficient, and (ii) comparing the calculated weighted sum with a predetermined threshold;

wherein if the weighted sum exceeds the predetermined threshold, the periodic extrapolation flag (pwef) is set to a first value; and

wherein is the weighted sum does not exceed the predetermined threshold, the periodic extrapolation flag is set to a second value.

15. The method of claim 14, wherein the first value is one and the second value is zero.

16. The method of claim 15, wherein the examining the predetermined number of samples of the other segment is performed in accordance with an analysis window;

and

wherein an amount of energy (E) within the analysis window in determined in accordance with the expression;

17. The method of claim 16, wherein lg is the base-2 logarithmic gain of the decoded signal (sq(n));

and

wherein if the amount of energy (E) is greater than zero, then the base-2 logarithmic gain lg equals log₂E.

18. The method of claim 17, wherein the determining of the normalized logarithmic signal gain (nlg) includes determining a long term average (lvl) of the logarithmic gain of an active portion of the decoded signal (sq(n));

and

wherein the normalized logarithmic signal gain (nlg) is determined in accordance with the equation;

nlg=lg−

lvl.

19. The method of claim 18, wherein the calculating the pitch prediction gain (ppg) is determined in accordance with the expression:

20. The method of claim 19, wherein the calculating of the first normalized autocorrelation coefficient(ρ

₁) is determined in accordance with the expression;

21. The method of claim 20, wherein the a normalized logarithmic signal gain (nlg), the pitch prediction gain (ppg), and the first normalized autocorrelation coefficient(ρ

₁) combine to form a single figure of merit (fom) representative of the decoded signal (sq(n)), the single figure of merit (fom) being determined in accordance with the normalized logarithmic signal gain (nlg), the pitch prediction gain (ppg), and the first normalized autocorrelation coefficient(ρ

₁); and

wherein a status of the periodic extrapolation flag (pwef) is based upon the figure of merit (fom).

22. The method of claim 21 wherein figure of merit (fom) is determined in accordance with the expression:

fom=nlg+1.25ppg+16ρ

₁.

23. The method of claim 22, further comprising searching for a second time lag (ppfe2) if (i) the periodic extrapolation flag (pwef) is a predetermined value and (ii) the first preliminary time lag (ppfe1) is less than a predetermined amount, the second time lag (ppfe2) being based upon the first time lag (ppfe1);

wherein the second time lag (ppfe2) is greater than or equal to the predetermined amount.

24. The method of claim 23, wherein the second time lag (ppfe2) maximizes the expression:

25. The method of claim 23, further comprising performing a second waveform extrapolation to extrapolate the at least one of the subsequent replacement frames based upon the second time lag (ppfe2).

26. The method of claim 25, wherein the at least one of the subsequent replacement frames is defined by the expression:

27. The method of claim 26, wherein the predetermined amount of time is about ten milliseconds.

28. The method of claim 27, further comprising determining sample magnitudes of the first preliminary time lag (ppfe1) and the second time lag (ppfe2).

29. The method of claim 28, wherein the sample magnitudes of the first preliminary time lag (ppfe1) and the second time lag (ppfe2) are respectively determined in accordance with the expressions:

30. The method of claim 29, wherein the waveforms sq(n) and sq₂(n) are combined in accordance with the expression:

sq(n)←

sq(n)+sq₂(n), for n=N+1 , N+2 ,. . . , N+N_f

where sq(n) is replaced by the sum of sq(n) and sq₂(n).

31. The method of claim 30, further comprising summing sample magnitudes of sq(n) in accordance with the expression:

32. The method of claim 31, further comprising scaling the summed waveform.

33. A method of synthesizing a number of corrupted frames output from a decoder including one or more predictive filters, the corrupted frames being representative of one segment of a decoded signal (sq(n)) output from the decoder, the method comprising:

determining, using at least one processor, a first preliminary time lag (ppfe1) based upon examining a predetermined number (K) of samples of another segment of the decoded signal;

determining, using the at least one processor, a scaling factor (ptfe) associated with the examined number (K) of samples, the scaling factor (ptfe) only being a function of (i) the first preliminary time lag (ppfe1) and (ii) the decoded signal (sq(n));

extrapolating, using the at least one processor, a first replacement frame based at least upon the first preliminary time lag (ppfe1) and the scaling factor (ptfe);

wherein subsequent replacement frames are extrapolated based upon a time lag and scaling factor found in the first replacement frame; and

correcting, using the at least one processor, internal states of the filters when a first good frame is received, the first good frame being received after the number of corrupted frames.

34. The method of claim 33, wherein the updating includes updating short-term and long-term synthesis filters associated with the one or more predictive filters.

35. The method of claim 34, wherein the updating of the short-term predictive filter is performed in accordance with the expression:

stsm(k)=sq(N+N_f+1−

k),k=1 ,2, . . . , M.

wherein,

stsm(k) represents the k-th memory value of a short-term synthesis filter associated with the short-term predictive filters;

(M) represents the last M samples of the one segment of the decoded signal;

(N) represents the number of decoder output speech samples in previous frames that are stored; and

N_f represent the number of samples in a frame.

36. The method of claim 35, wherein the updating of the long-term synthesis filter includes updating content of an internal memory and extrapolating a predetermined number of samples (L) of a first of the replacement frames in accordance with the expression:

ltsm(n)=ptfe1×

ltsm(n−

ppfe1), for n=N+1, N+2, . . . , N+L.

37. The method of claim 36, wherein the updating further includes overlap-adding the content of the internal memory with a ringing of the long-term synthesis filter in accordance with the expression:

ltsm(N+n)←

w_u(n)ltsm(N+n)+w_d(n)ltr(n), for n=1, 2, . . . , L;

where w_u represents a windowing function associated with the first of the replacement waveforms.

38. An apparatus for synthesizing a number of corrupted frames output from a decoder including one or more predictive filters, the corrupted frames being representative of one segment of a decoded signal (sq(n)) output from the decoder, the apparatus comprising:

at least one processor;

means for determining, using the at least one processor, a first preliminary time lag (ppfe1) based upon examining a predetermined number (K) of samples of another segment of the decoded signal;

means for determining, using the at least one processor, a scaling factor (ptfe) associated with the examined number (K) of samples, the scaling factor (ptfe) only being a function of (i) the first preliminary time lag (ppfe1) and (ii) the decoded signal (sq(n)); and

means for extrapolating, using the at least one processor, a first replacement frame based upon the first preliminary time lag (ppfe1) and the scaling factor (ptfe).

39. The apparatus of claim 38, further comprising means for updating internal states of the filters based upon the extrapolating.

40. An apparatus for synthesizing a number of corrupted frames output from a decoder including one or more predictive filters, the corrupted frames being representative of one segment of a decoded signal (sq(n)) output from the decoder, the apparatus comprising:

at least one processor;

means for determining, using the at least one processor, a first preliminary time lag (ppfe1) based upon examining a predetermined number (K) of samples of another segment of the decoded signal;

means for determining, using the at least one processor, a scaling factor (ptfe) associated with the examined number (K) of samples, the scaling factor (ptfe) only being a function of (i) the first preliminary time lag (ppfe1) and (ii) the decoded signal (sq(n));

means for extrapolating, using the at least one processor, a first replacement frame based at least upon the first preliminary time lag (ppfe1) and the scaling factor (ptfe);

wherein subsequent replacement frames are extrapolated based upon a time lag and scaling factor found in the first replacement frame; and

means for correcting, using the at least one processor, internal states of the filters when a first good frame is received, the first good frame being received after the number of corrupted frames.

41. The apparatus of claim 40, wherein the updating includes updating short-term and long-term synthesis filters associated with the one or more predictive filters.

42. A computer usable storage medium carrying one or more sequences of one or more instructions for execution by one or more processors to perform a method of synthesizing a number of corrupted frames output from a decoder including one or more predictive filters, the corrupted frames being representative of one segment of a decoded signal (sq(n)) output from the decoder, the instructions when executed by the one or more processors, cause the one or more processors to perform the steps of:

determining a first preliminary time lag (ppfe1) based upon examining a predetermined number (K) of samples of another segment of the decoded signal;

determining a scaling factor (ptfe) associated with the examined number (K) of samples, the scaling factor (ptfe) only being a function of (i) the first preliminary time lag (ppfe1) and (ii) the decoded signal (sq(n)); and

extrapolating a first replacement frame based upon the first preliminary time lag (ppfe1) and the scaling factor (ptfe);

wherein subsequent replacement frames are extrapolated based upon a time lag and scaling factor found in the first replacement frame.

43. The computer usable storage medium of claim 42, further causing the one or more processors to update internal states of the filters based upon the extrapolating.

44. A computer usable storage medium carrying one or more sequences of one or more instructions for execution by one or more processors to perform a method for synthesizing a number of corrupted frames output from a decoder including one or more predictive filters, the corrupted frames being representative of one segment of a decoded signal (sq(n)) output from the decoder, the instructions when executed by the one or more processors, cause the one or more processors to perform the steps of:

determining a first preliminary time lag (ppfe1) based upon examining a predetermined number (K) of samples of another segment of the decoded signal;

determining a scaling factor (ptfe) associated with the examined number (K) of samples, the scaling factor (ptfe) only being a function of (i) the first preliminary time lag (ppfe1) and (ii) the decoded signal (sq(n));

extrapolating a first replacement frame based at least upon the first preliminary time lag (ppfe1) and the scaling factor (ptfe);

wherein subsequent replacement frames are extrapolated based upon a time lag and scaling factor found in the first replacement frame; and

correcting internal states of the filters when a first good frame is received, the first good frame being received after the number of corrupted frames.

45. The computer usable storage medium of claim 44, wherein the updating includes updating short-term and long-term synthesis filters associated with the one or more predictive filters.