Method of bandwidth extension for narrow-band speech

1. A method of producing a wideband signal from a narrowband signal, the method comprising:

computing M nb area coefficients from the narrowband signal;

interpolating the M nb area coefficients into M wb area coefficients;

generating a highband signal using the M wb area coefficients; and

combining the highband signal with the narrowband signal interpolated to the highband sampling rate to form the wideband signal.

2. The method of claim 1 , wherein computing M nb area coefficients further comprises computing M nb area coefficient using the following equation:

A

i

=

1

+

r

i

1

-

r

i

⁢

A

i

+

1

;

i

=

M

nb

,

M

nb

-

1

,

…

⁢

,

1

,

where A 1 corresponds to a cross-section at the lips, A M nb +1 correspond to cross-sections of the vocal tract at the glottis opening and r i are reflection coefficients.

3. The method of claim 1 , wherein interpolating the M nb area coefficients into M wb area coefficients further comprises interpolating using a linear first order polynomial interpolation scheme.

4. The method of claim 1 , wherein interpolating the M nb area coefficients further comprises interpolating using a cubic spline interpolation scheme.

5. The method of claim 1 , wherein interpolating the M nb area coefficients further comprises interpolating using a fractal interpolation scheme.

6. The method of claim 1 , further comprising:

insuring that the interpolated M wb area coefficients are positive; and

setting A M wb +1 wb to a finite positive fixed value.

7. The method of claim 1 , wherein interpolating the M nb area coefficients further comprises interpolating by a factor of 2, with a ¼ sampling interval shift.

8. A method of bandwidth extension of a narrowband signal, the method comprising:

computing M nb log-area coefficients from the narrowband signal;

interpolating the M nb log-area coefficients into M wb log-area coefficients;

generating a highband signal using the interpolated M wb log-area coefficients; and

combining the highband signal with the narrowband signal interpolated to the highband sampling rate to generate a wideband signal.

9. The method of claim 8 , wherein computing M nb log-area coefficients further comprises computing M nb area coefficients using the equation below and computing their logarithmic values:

A

i

=

1

+

r

i

1

-

r

i

⁢

A

i

+

1

;

i

=

M

nb

,

M

nb

-

1

,

…

⁢

,

1

,

where A 1 corresponds to a cross-section at the lips, A M nb +1 correspond to cross-sections of the vocal tract at the glottis opening and r i are reflection coefficients.

10. The method of claim 8 , wherein interpolating the M nb log-area coefficients further comprises interpolating using a linear first order polynomial interpolation scheme.

11. The method of claim 8 , wherein interpolating the M nb log-area coefficients further comprises interpolating using a cubic spline interpolation scheme.

12. The method of claim 8 , wherein interpolating the M nb log-area coefficients further comprises interpolating using a fractal interpolation scheme.

13. The method of claim 8 , wherein interpolating the M nb log-area coefficients further comprises interpolating by a factor of 2, with a ¼ sample shift.

14. A method of extending the bandwidth of a narrowband signal, a preprocessing of the narrowband signal producing narrowband partial correlation coefficients (parcors), the method comprising:

(1) computing M nb area coefficients from the narrowband parcors;

(2) computing M nb log-area coefficients from the M nb area coefficients;

(3) obtaining M wb log-area coefficients from the M nb log-area coefficients;

(4) computing M wb area coefficients from the M wb log-area coefficients;

(5) computing wideband parcors from the M wb area coefficients;

(6) generating a highband signal using the wideband parcors; and

(7) combining the highband signal with the narrowband signal interpolated to the highband sampling rate.

15. The method of extending the bandwidth of a narrowband signal of claim 14 , wherein obtaining M wb log-area coefficients further comprises obtaining M nb times two log-area coefficients using interpolation.

16. A method of producing a wideband signal from a narrowband signal, the method comprising:

(1) computing narrowband linear predictive coefficients (LPCs) from the narrowband signal;

(2) computing narrowband parcors r i associated with the narrowband LPCs;

(3) computing M nb area coefficients A i nb , i=1, 2, . . . , M nb using the following:

A

i

=

1

+

r

i

1

-

r

i

⁢

A

i

+

1

;

i

=

M

nb

,

M

nb

-

1

,

…

⁢

,

1

,

where A 1 corresponds to a cross-section at lips, A M nb +1 and corresponds to a cross-section of a vocal tract at a glottis opening;

(4) extracting M wb area coefficients from the M nb area coefficients using interpolation;

(5) computing wideband parcors using the M wb area coefficients according to the following:

r

i

wb

=

A

i

wb

-

A

i

+

1

wb

A

i

wb

+

A

i

+

1

wb

,

i

=

1

,

2

,

…

⁢

,

M

wb

;

(6) computing wideband LPCs a i wb , i=1, 2, . . . , M wb , from the wideband parcors; and

(7) synthesizing a wideband signal y wb using the wideband LPCs and an excitation signal.

17. The method of producing a wideband signal from a narrowband signal of claim 16 , the method further comprising:

(8) highpass filtering the wideband signal y wb to generate a highband signal; and

(9) combining the highband signal with the narrowband signal interpolated to the wideband sampling rate to produce a wideband signal Ŝ wb .

18. The method of producing a wideband signal from a narrowband signal of claim 16 , wherein extracting M wb area coefficients from the M nb area coefficients using shifted-interpolation further comprises interpolating by a factor of 4 followed by a single sample shift and decimating by a factor of 2.

19. The method of producing a wideband signal from a narrowband signal of claim 16 , the method further comprising:

(8) generating the excitation signal from a narrowband prediction residual signal using fullwave rectification.

20. The method of producing a wideband signal from a narrowband signal of claim 16 , wherein M wb equals two times M nb .

21. The method of producing a wideband signal from a narrowband signal of claim 16 , wherein extracting M wb area coefficients from the M nb area coefficients using shifted-interpolation further comprises interpolating by a factor of 2 with a ¼ sample shift.

22. The method of producing a wideband signal from a narrowband signal of claim 16 , wherein extracting M wb area coefficients from the M nb area coefficients using shifted-interpolation further comprises using a first order linear shifted-interpolation.

23. The method of producing a wideband signal from a narrowband signal of claim 16 , wherein extracting M wb area coefficients from the M nb area coefficients using shifted-interpolation further comprises using cubic-spline interpolation.

24. The method of producing a wideband signal from a narrowband signal of claim 16 , wherein extracting M wb area coefficients from the M nb area coefficients using shifted-interpolation further comprises using fractal interpolation.

25. A method of extending the bandwidth of a narrowband signal, the method comprising:

(1) computing narrowband linear predictive coefficients (LPCs) from the narrowband signal;

(2) computing narrowband parcors associated with the narrowband LPCs;

(3) computing M nb area coefficients using the narrowband parcors;

(4) extracting M wb area coefficients from the M nb area coefficients using shifted-interpolation;

(5) converting the M wb area coefficients into wideband LPCs; and

(6) synthesizing a wideband signal y wb using the wideband LPCs and an excitation signal.

26. The method of extending the bandwidth of a narrowband signal of claim 25 , the method further comprising:

(7) highpass filtering the wideband signal y wb to produce a highband signal; and

(8) combining the highband signal with the narrowband signal interpolated to the wideband sampling rate to produce a wideband signal Ŝ wb .

27. The method of extending the bandwidth of a narrowband signal of claim 25 , wherein the step of converting the M wb area coefficients into wideband LPCs further comprising computing wideband parcors from the M wb area coefficients and using step-down back-recursion to compute the wideband LPCs.

28. The method of extending the bandwidth of a narrowband signal of claim 25 , the method further comprising computing the excitation signal from a narrowband prediction residual signal.

29. The method of extending the bandwidth of a narrowband signal of claim 25 , wherein the higher band of the excitation signal is highpass filtered white noise.

30. A method of extending the bandwidth of a narrowband signal, the method comprising:

(1) computing narrowband linear predictive coefficients (LPCs) from the narrowband signal;

(2) computing M nb area coefficients using the narrowband LPCs;

(3) extracting M wb area coefficients from the M nb area coefficients using interpolation;

(4) converting the M wb area coefficients into wideband LPCs; and

(5) synthesizing a wideband signal y wb using the wideband LPCs and highpass filtered white noise in the higher band of an excitation signal and a linear prediction residual signal in the lower band of the excitation signal.

31. The method of extending the bandwidth of a narrowband signal of claim 30 , wherein computing the excitation signal from a narrowband prediction residual signal further comprises inverse filtering the narrowband signal.

32. A method of producing a wideband signal from a narrowband signal, the method comprising:

(1) producing a wideband excitation signal from the narrowband signal;

(2) computing partial correlation coefficients r i (parcors) from the narrowband signal;

(3) computing M nb area coefficients according to the following equation:

A

i

=

1

+

r

i

1

-

r

i

⁢

A

i

+

1

;

i

=

M

nb

,

M

nb

-

1

,

…

⁢

,

1

,

where A 1 corresponds to the cross-section at lips and A M nb +1 corresponds to the cross-section at a glottis opening;

(4) extracting M wb area coefficients from the M nb area coefficients using interpolation;

(5) computing wideband parcors r i wb from the interpolated M wb area coefficients according to the following:

r

i

wb

=

A

i

wb

-

A

i

+

1

wb

A

i

wb

+

A

i

+

1

wb

,

i

=

1

,

2

,

…

⁢

,

M

wb

;

(6) computing wideband linear predictive coefficients (LPCs) a i wb from the wideband parcors r i wb ;

(7) synthesizing a wideband signal y wb from the wideband LPCs a i wb and the wideband excitation signal;

(8) highpass filtering the wideband signal y wb to produce a highband signal; and

(9) generating a wideband signal Ŝ wb by summing the highband signal and the narrowband signal interpolated to the wideband sampling rate.

33. The method of producing a wideband signal from a narrowband signal of claim 32 , wherein producing the wideband excitation signal from the narrowband signal further comprises:

performing linear prediction on the narrowband signal to find a i wb LP coefficients;

interpolating the narrowband signal to produce an upsampled narrowband signal;

producing a narrowband residual signal {tilde over (r)} nb by inverse filtering the upsampled interpolated narrowband signal using a transfer function associated with the a i wb LP coefficients; and

generating the wideband excitation signal from the narrowband residual signal {tilde over (r)} nb .

34. A method of producing a wideband signal from a narrowband signal, the method receiving data associated with a narrowband signal, the method comprising:

(1) computing M nb area coefficients using the narrowband data;

(2) extracting M wb area coefficients from the M nb area coefficients using interpolation; and

(3) synthesizing a wideband signal y wb using wideband coefficients processed from data associated with the M nb area coefficients and an excitation signal.

35. The method of producing a wideband signal from a narrowband signal of claim 34 , the method further comprising:

(4) highpass filtering the wideband signal y wb to form a highband signal; and

(5) generating a wideband signal Ŝ wb by summing the highband signal and the narrowband signal interpolated to the wideband sampling rate.

36. A method of producing a wideband signal from a narrowband signal, the method comprising:

(1) computing M nb area coefficients from the narrowband signal;

(2) computing M nb log-area coefficients from the M nb area coefficients;

(3) interpolating the M nb log-area coefficients into M wb log-area coefficients;

(4) converting the M wb log-area coefficients into M wb area coefficients; and

(5) synthesizing a wideband signal y wb using the M wb area coefficients and an excitation signal.

37. The method of producing a wideband signal from a narrowband signal of claim 36 , the method further comprising:

(6) highpass filtering the wideband signal y wb to produce a highband signal; and

(7) combining the highband signal with the narrowband signal interpolated to the wideband sampling rate to generate a wideband signal Ŝ wb .

38. The method of claim 36 , wherein computing M nb area coefficients further comprises computing M nb area coefficients using the following equation:

A

i

=

1

+

r

i

1

-

r

i

⁢

A

i

+

1

;

⁢

i

=

M

nb

,

M

nb

-

1

,

…

,

1

,

where A 1 corresponds to a cross-section at the lips, A M nb +1 corresponds to a cross-section at the glottis opening and r i are reflection coefficients.

39. The method of claim 36 , wherein interpolating the M nb log-area coefficients into M wb log-area coefficients further comprises interpolating using a linear first order polynomial interpolation scheme.

40. The method of claim 36 , wherein interpolating the M nb log-area coefficients further comprises interpolating using a cubic spline interpolation scheme.

41. The method of claim 36 , wherein interpolating the M nb log-area coefficients further comprises interpolating using a fractal interpolation scheme.

42. The method of claim 36 , wherein interpolating the M nb log-area coefficients further comprises interpolating by a factor of 2, with a ¼ sample shift.

43. The method of claim 36 , wherein interpolating the M nb log-area coefficients further comprises interpolating by a factor of 4 followed by a single sample shift and decimating by a factor of 2.

44. A method of generating a wideband signal from a narrowband signal, the method comprising:

(1) producing a wideband excitation signal from the narrowband signal;

(2) computing partial correlation coefficients r i (parcors) from the narrowband signal;

(3) computing M nb area coefficients according to the following equation:

A

i

=

1

+

r

i

1

-

r

i

⁢

A

i

+

1

;

⁢

i

=

M

nb

,

M

nb

-

1

,

…

,

1

,

where A 1 corresponds to the cross-section at lips and A M nb +1 corresponds to the cross-section at a glottis opening;

(4) computing M nb log-area coefficients by applying a log operator to the M nb area coefficients;

(5) extracting M wb log-area coefficients from the M nb log-area coefficients using shifted-interpolation;

(6) converting the M wb log-area coefficients into M wb area coefficients;

(7) computing wideband parcors r i wb from the M wb area coefficients according to the following:

r

i

wb

=

A

i

wb

-

A

i

+

1

wb

A

i

wb

+

A

i

+

1

wb

,

⁢

i

=

1

,

2

,

…

,

M

wb

;

(8) computing wideband linear predictive coefficients (LPCs) a i wb from the wideband parcors r i wb ; and

(9) synthesizing a wideband signal y wb from the wideband LPCs a i wb and the wideband excitation signal.

45. The method of generating an output wideband signal from a narrowband signal of claim 44 , the method further comprising:

(10) highpass filtering the wideband signal y wb to generate a highband signal S hb ; and

(11) generating a wideband signal Ŝ wb by summing the highband signal S hb and the narrowband signal interpolated to the wideband sampling rate.

46. The method of generating a wideband signal from a narrowband signal of claim 44 , wherein producing a wideband excitation signal from the narrowband signal further comprises:

performing linear prediction on the narrowband signal to find a i wb LP coefficients;

interpolating the narrowband signal to produce an upsampled interpolated narrowband signal;

producing a narrowband residual signal {tilde over (r)} nb by inverse filtering the upsampled interpolated narrowband signal using a transfer function associated with the a i wb LP coefficients; and

generating a wideband excitation signal from the narrowband residual signal {tilde over (r)} nb .

47. A method of producing a wideband signal from a narrowband signal, the method comprising:

computing M nb area coefficients from the narrowband signal;

interpolating the M nb area coefficients into M wb area coefficients; and

generating the wideband signal using the M wb area coefficients.

48. The method of generating a wideband signal from a narrowband signal of claim 47 , wherein interpolating the M nb area coefficients further comprises interpolating by a factor of 4 followed by a single sampling interval shift and decimating by a factor of 2.

49. A method of producing a wideband signal from a narrowband signal, the method comprising:

computing M nb log-area coefficients by applying a log operator to M nb area coefficients generated from the narrowband signal;

extracting M wb log-area coefficients from the M nb log-area coefficients using interpolation; and

generating a wideband signal using M wb area coefficients generated from the M wb log-area coefficients.

50. The method of generating a wideband signal from a narrowband signal of claim 49 , wherein extracting the M nb log-area coefficients using interpolation further comprises interpolating by a factor of 4 followed by a single sampling interval shift and decimating by a factor of 2.