Perceptual weighting device and method for efficient coding of wideband signals

• US 20050108007A1
• Filed: 10/18/2004
• Published: 05/19/2005
• Est. Priority Date: 10/27/1998
• Status: Abandoned Application

• Current Assignee: Saint Lawrence Communications LLC (Acacia Research Corporation)
• Original Assignee: VoiceAge Corporation
• Inventors: Salami, Redwan, Bessette, Bruno, Lefebvre, Roch
• Application Number:
  US10/965,795
• Publication Number:
  US 20050108007A1
• Time in Patent Office: Days
• US Class Current: 704/223
• CPC Class Codes: G10L 19/26 Pre-filtering or post-filtering
• CPC Class Codes: G10L 2019/0011 Long term prediction filters, i.e. pitch estimation

Abstract

A perceptual weighting device for producing a perceptually weighted signal in response to a wideband signal comprises a signal pre-emphasis filter, a synthesis filter calculator, and a perceptual weighting filter. The signal pre-emphasis filter enhances the high frequency content of the wideband signal to thereby produce a pre-emphasized signal. The signal pre-emphasis filter has a transfer function of the form: P(z)=1−μz⁻¹, wherein μ is a pre-emphasis factor having a value located between 0 and 1. The synthesis filter calculator is responsive to the pre-emphasized signal for producing synthesis filter coefficients. Finally, the perceptual weighting filter processes the pre-emphasized signal in relation to the synthesis filter coefficients to produce the perceptually weighted signal. The perceptual weighting filter has a transfer function, with fixed denominator, of the form: W(z)=A(z/γ₁)/(1−γ₂z⁻¹) where 0<γ₂<γ₁≦1.

Claims

1. A perceptual weighting device for producing a perceptually weighted signal in response to a wideband signal in order to reduce a difference between a weighted wideband signal and a subsequently synthesized weighted wideband signal, said perceptual weighting device comprising:

a) a signal preemphasis filter responsive to the wideband signal for enhancing a high frequency content of the wideband signal to thereby produce a preemphasised signal;

b) a synthesis filter calculator responsive to said preemphasised signal for producing synthesis filter coefficients; and

c) a perceptual weighting filter, responsive to said preemphasised signal and said synthesis filter coefficients, for filtering said preemphasised signal in relation to said synthesis filter coefficients to thereby produce said perceptually weighted signal, said perceptual weighting filter having a transfer function with fixed denominator whereby weighting of said wideband signal in a formant region is substantially decoupled from a spectral tilt of said wideband signal.

2. A perceptual weighting device as defined in claim 1, wherein said signal preemphasis filter has a transfer function of the form:

P(z)=1−

μ

z<sup>−

1</sup>

wherein μ

is a preemphasis factor having a value located between 0 and 1.

3. A perceptual weighting device as defined in claim 2, wherein said preemphasis factor μ

is 0.7.

4. A perceptual weighting device as defined in claim 2, wherein said perceptual weighting filter has a transfer function of the form:

W(z)=A(z/γ

₁)/(1−

γ

₂z<sup>−

1</sup>)

where 0≦

γ

₂≦

γ

₁≦

1 and γ

₂ and γ

₁ are weighting control values.

5. A perceptual weighting device as defined in claim 4, wherein γ

₂ is set equal to μ

.

6. A perceptual weighting device as defined in claim 1, wherein said perceptual weighting filter has a transfer function of the form:

W(z)=A(z/γ

₁)/(1−

γ

₂z<sup>−

1</sup>)

where 0≦

γ

₂≦

γ

₁≦

1 and γ

₂ and y₁ are weighting control values.

7. A perceptual weighting device as defined in claim 6, wherein γ

₂ is set equal to μ

.

15. An encoder for encoding a wideband signal, comprising:

a) a perceptual weighting device as recited in claim 1;

b) an pitch codebook search device responsive to said perceptually weighted signal for producing pitch codebook parameters and an innovative search target vector;

c) an innovative codebook search device, responsive to said synthesis filter coefficients and to said innovative search target vector, for producing innovative codebook parameters; and

d) a signal forming device for producing an encoded wideband signal comprising said pitch codebook parameters, said innovative codebook parameters, and said synthesis filter coefficients.

16. An encoder as defined in claim 15, wherein said signal preemphasis filter has a transfer function of the form:

P(z)=1−

μ

z<sup>−

1</sup>

wherein μ

is a preemphasis factor having a value located between 0 and 1.

17. An encoder as defined in claim 16, wherein said preemphasis factor μ

is 0.7.

18. An encoder as defined in claim 16, wherein said perceptual weighting filter has a transfer function of the form:

W(z)=A(z/γ

₁)/(1−

γ

₂z<sup>−

1</sup>)

where 0<

γ

₂<

γ

₁≦

1 and γ

₂ and γ

₁ are weighting control values.

19. An encoder as defined in claim 18, wherein γ

₂ is set equal to μ

.

20. An encoder as defined in claim 15, wherein said perceptual weighting filter has a transfer function of the form:

W(z)=A(z/γ

₁)/(1−

γ

₂z<sup>−

1</sup>)

where 0<

γ

₂<

γ

₁≦

1 and Y₂ and γ

₁ are weighting control values.

21. An encoder as defined in claim 20, wherein μ

is set equal to γ

₂.

22. A cellular communication system for servicing a large geographical area divided into a plurality of cells, comprising:

a) mobile transmitter/receiver units;

b) cellular base stations respectively situated in said cells;

c) a control terminal for controlling communication between the cellular base stations;

d) a bidirectional wireless communication sub-system between each mobile unit situated in one cell and the cellular base station of said one cell, said bidirectional wireless communication sub-system comprising, in both the mobile unit and the cellular base station;

i) a transmitter including an encoder for encoding a wideband signal as recited in claim 15 and a transmission circuit for transmitting the encoded wideband signal; and

ii) a receiver including a receiving circuit for receiving a transmitted encoded wideband signal and a decoder for decoding the received encoded wideband signal.

23. A cellular communication system as defined in claim 22, wherein said signal preemphasis filter has a transfer function of the form:

P(z)=1−

μ

z<sup>−

1</sup>

wherein μ

is a preemphasis factor having a value located between 0 and 1.

24. A cellular communication system as defined in claim 23, wherein said preemphasis factor μ

is 0.7.

25. A cellular communication system as defined in claim 23, wherein said perceptual weighting filter has a transfer function of the form:

W(z)=A(z/γ

₁)/(1−

γ

₂z<sup>−

1</sup>)

where 0<

γ

₂<

γ

₁≦

1 and γ

₂ and γ

₁ are weighting control values.

26. A cellular communication system as defined in claim 25, wherein μ

is set equal to γ

₂.

27. A cellular communication system as defined in claim 22, wherein said perceptual weighting filter has a transfer function of the form:

W(z)=A(z/γ

₁)/(1−

γ

₂z<sup>−

1</sup>)

where 1<

γ

₂<

γ

₁≦

1 and γ

₂ and γ

₁ are weighting control values.

28. A cellular communication system as defined in claim 27, wherein γ

₂ is set equal to μ

.

29. A cellular mobile transmitter/receiver unit comprising:

a) a transmitter including an encoder for encoding a wideband signal as recited in claim 15 and a transmission circuit for transmitting the encoded wideband signal; and

b) a receiver including a receiving circuit for receiving a transmitted encoded wideband signal and a decoder for decoding the received encoded wideband signal.

30. A cellular mobile transmitter/receiver unit as defined in claim 29, wherein said signal preemphasis filter has a transfer function of the form:

P(z)=1−

μ

z<sup>−

1</sup>

wherein μ

is a preemphasis factor having a value located between 0 and 1.

31. A cellular mobile transmitter/receiver unit as defined in claim 30, wherein said preemphasis factor μ

is 0.7.

32. A cellular mobile transmitter/receiver unit as defined in claim 30, wherein said perceptual weighting filter has a transfer function of the form:

W(z)=A(z/γ

₁)/(1−

γ

₂z<sup>−

1</sup>)

where 0<

γ

₂<

γ

₁≦

1 and γ

₂ and γ

₁ are weighting control values.

33. A cellular mobile transmitter/receiver unit as defined in claim 32, wherein γ

₂ is set equal to μ

.

34. A cellular mobile transmitter/receiver unit as defined in claim 29, wherein said perceptual weighting filter has a transfer function of the form:

W(z)=A(z/γ

₁)/(1−

γ

₂z<sup>−

1</sup>)

where 0<

γ

₂<

γ

₁≦

1 and γ

₂ and γ

₁ are weighting control values.

35. A cellular mobile transmitter/receiver unit as defined in claim 34, wherein γ

₂ is set equal to μ

.

36. A cellular network element comprising:

a) a transmitter including an encoder for encoding a wideband signal as defined in claim 15 and a transmission circuit for transmitting the encoded wideband signal; and

b) a receiver including a receiving circuit for receiving a transmitted encoded wideband signal and a decoder for decoding the received encoded wideband signal.

37. A cellular network element as defined in claim 36, wherein said signal preemphasis filter has a transfer function of the form:

P(z)=1−

μ

z<sup>−

1</sup>

wherein μ

is a preemphasis factor having a value located between 0 and 1.

38. A cellular network element as defined in claim 37, wherein said preemphasis factor μ

is 0.7.

39. A cellular network element as defined in claim 37, wherein said perceptual weighting filter has a transfer function of the form:

W(z)=A(z/γ

₁)/(1−

γ

₂z<sup>−

1</sup>)

where 0<

γ

₂<

γ

₁≦

1 and γ

₂ and γ

₁ are weighting control values.

40. A cellular network element as defined in claim 39, wherein γ

₂ is set equal to μ

.

41. A cellular network element as defined in claim 36, wherein said perceptual weighting filter has a transfer function of the form:

W(z)=A(z/γ

₁)/(1−

γ

₂z<sup>−

1</sup>)

where 0<

γ

₂<

γ

₁≦

1 and γ

₂ and γ

₁ are weighting control values.

42. A cellular network element as defined in claim 41, wherein μ

is set equal to μ

₂.

43. In a cellular communication system for servicing a large geographical area divided into a plurality of cells, comprising:

mobile transmitter/receiver units;

cellular base stations, respectively situated in said cells; and

control terminal for controlling communication between the cellular base stations;

a bidirectional wireless communication sub-system between each mobile unit situated in one cell and the cellular base station of said one cell, said bidirectional wireless communication sub-system comprising, in both the mobile unit and the cellular base station;

a) a transmitter including an encoder for encoding a wideband signal as recited in claim 15 and a transmission circuit for transmitting the encoded wideband signal; and

b) a receiver including a receiving circuit for receiving a transmitted encoded wideband signal and a decoder for decoding the received encoded wideband signal.

44. A bidirectional wireless communication sub-system as defined in claim 43, wherein said signal preemphasis filter has a transfer function of the form:

P(z)=1−

μ

z<sup>−

1</sup>

wherein μ

is a preemphasis factor having a value located between 0 and 1.

45. A bidirectional wireless communication sub-system as defined in claim 44, wherein said preemphasis factor μ

is 0.7.

46. A bidirectional wireless communication sub-system as defined in claim 44, wherein said perceptual weighting filter has a transfer function of the form:

W(z)=A(z/γ

₁)/(1−

γ

₂z<sup>−

1</sup>)

where 0<

γ

₂<

γ

₁≦

1 and γ

₂ and γ

₁ are weighting control values.

47. A bidirectional wireless communication sub-system as defined in claim 46, wherein μ

is set equal to γ

₂.

48. A bidirectional wireless communication sub-system as defined in claim 43, wherein said perceptual weighting filter has a transfer function of the form:

W(z)=A(z/γ

₁)/(1−

γ

₂z<sup>−

1</sup>)

where 0<

γ

₂<

γ

₂≦

1 and γ

₂ and γ

₁ are weighting control values.

49. A bidirectional wireless communication sub-system as defined in claim 48, wherein γ

₂ is set equal to μ

.

8. A method for producing a perceptually weighted signal in response to a wideband signal in order to reduce a difference between a weighted wideband signal and a subsequently synthesized weighted wideband signal, said method comprising:

a) filtering the wideband signal to produce a preemphasised signal with enhanced high frequency content;

b) calculating, from said preemphasised signal, synthesis filter coefficients; and

c) filtering said preemphasised signal in relation to said synthesis filter coefficients to thereby produce a perceptually weighted speech signal, wherein said filtering comprises processing the preemphasis signal through a perceptual weighting filter having a transfer function with fixed denominator whereby weighting of said wideband signal in a formant region is substantially decoupled from a spectral tilt of said wideband signal.

9. A method for producing a perceptually weighted signal as defined in claim 8, wherein filtering the wideband signal comprises filtering through a transfer function of the form:

P(z)=1−

μ

z<sup>−

1</sup>

wherein μ

is a preemphasis factor having a value located between 0 and 1.

10. A method for producing a perceptually weighted signal as defined in claim 9, wherein said preemphasis factor μ

is 0.7.

11. A method for producing a perceptually weighted signal as defined in claim 9, wherein said perceptual weighting filter has a transfer function of the form:

W(z)=A(z/γ

₁)/(1−

γ

₂z<sup>−

1</sup>)

where 0≦

γ

₂<

γ

₁≦

1 and γ

₂ and γ

₁ are weighting control values.

12. A method for producing a perceptually weighted signal as defined in claim 11, wherein γ

₂ is set equal to μ

.

13. A method for producing a perceptually weighted signal as defined in claim 8, wherein said perceptual weighting filter has a transfer function of the form:

W(z)=A(z/γ

₁)/(1−

γ

₂z<sup>−

1</sup>)

where 0<

γ

₂<

γ

₁≦

1 and γ

₂ and γ

₁ are weighting control values.

14. A method for producing a perceptually weighted signal as defined in claim 13, wherein γ

₂ is set equal to μ

.