Controlling a weighting filter based on the spectral content of a speech signal

• US 20020116182A1
• Filed: 09/13/2001
• Published: 08/22/2002
• Est. Priority Date: 09/15/2000
• Status: Active Grant

• Current Assignee: MACOM Technology Solutions Holdings, Inc.
• Original Assignee: Conexant Systems Incorporated (Synaptics Incorporated)
• Inventors: Gao, Yang, Su, Huan-Yu
• Granted Patent: US 7,010,480 B2
• Time in Patent Office: Days
• US Class Current: 704/205
• CPC Class Codes: G10L 19/265 Pre-filtering, e.g. high frequency emphasis prior to encoding
• CPC Class Codes: G10L 21/0364 for improving intelligibility

Abstract

A method for preparing a speech signal for encoding comprises determining whether the spectral content of an input speech signal is representative of a defined spectral characteristic (e.g., a defined characteristic slope). A frequency specific filter component of a weighting filter is controlled based on the determination of the spectral content of the speech signal or/and its location in the encoder. A core weighting filter component of the weighting filter may be maintained regardless of the spectral content of the speech signal.

Claims

1. A method for preparing a speech signal for encoding, the method comprising:

determining whether the spectral content of an input speech signal is representative of a defined spectral characteristic;

controlling a frequency specific filter component of a weighting filter based on at least one of the determination of the spectral content of the speech signal; and

on an affiliation of the weighting filter with a particular portion of the encoder; and

maintaining a core weighting filter component of the weighting filter regardless of the spectral content of the speech signal.

2. The method according to claim 1 wherein the determining step comprises determining a defined spectral slope as the defined spectral characteristic.

3. The method according to claim 1 wherein the controlling step comprises controlling a low-pass filter component of a pre-processing weighting filter as the weighting filter, the controlling based on the determination of the spectral content of the speech signal.

4. The method according to claim 1 wherein the controlling step comprises controlling a high-pass filter component of a fixed codebook weighting filter as the weighting filter, the controlling based on the determination of the spectral content of the speech signal.

5. The method according to claim 1 wherein the controlling step comprises activating a low-pass filter component of a pre-processing filter as the weighting filter, if the spectral content of the speech signal is consistent with a low frequency energy that falls below a low frequency energy threshold.

6. The method according to claim 1 wherein the controlling step comprises changing filter parameters of a low-pass filter component of a pre-processing filter as the weighting filter to increase a contribution of the low-pass filter component to the resultant spectral response of the pre-processing weighting filter, if the spectral content of the speech signal is consistent with a low frequency energy that falls below a low frequency energy threshold.

7. The method according to claim 1 wherein the controlling step comprises controlling a high-pass filter component of a fixed codebook weighting filter as the weighting filter in response to the detection or absence of at least one of unwanted background noise and a noisy speech component of the input speech signal.

8. The method according to claim 1 wherein the controlling step comprises activating a high-pass filter component of a fixed codebook weighting filter as the weighting filter in response to the detection of background noise or undesired noise that meets or exceeds a threshold magnitude level over a certain spectral range.

9. The method according to claim 1 wherein the controlling step comprises controlling an adaptive codebook weighting filter as the weighting filter, the controlling based on a determination of the spectral content of the speech signal.

10. The method according to claim 1 wherein the controlling step comprises controlling filter parameters of an adaptive codebook weighting filter in response to the determination of the spectral content of the speech signal.

11. A method for preparing a speech signal for encoding, the method comprising:

determining whether the spectral content of an input speech signal is representative of a defined characteristic slope;

controlling a low-pass filter component of a pre-processing weighting filter based on the determination of the spectral content of the speech signal; and

maintaining a core weighting filter component of the pre-processing weighting filter regardless of the spectral content of the speech signal.

12. The method according to claim 11 wherein the determining comprises determining whether the spectral slope of the input speech signal conforms to a modified intermediate reference system spectral response as the defined characteristic slope.

13. The method according to claim 11 wherein the determining comprises determining whether the spectral slope of the input speech signal conforms to an intermediate reference system spectral response as the defined characteristic slope.

14. The method according to claim 11 wherein the controlling comprises activating the low-pass filter component in response to the detection of a spectral tilt of the input speech signal that is below a low frequency threshold.

15. The method according to claim 11 wherein the controlling comprises deactivating the low-pass filter component in response to the detection of a spectral tilt of the input speech signal that meets or exceeds a low frequency threshold.

16. The method according to claim 11 wherein the controlling comprises changing a filter parameter in response to the detection of the presence or the absence of a spectral tilt in the speech signal.

17. The method according to claim 11 wherein the determining determines that a low frequency energy falls below a low frequency energy threshold, and wherein the controlling changes the filter parameters of the low-pass filter component to activate or increase a contribution from the low-pass components of the weighted signal.

18. The method according to claim 11 wherein the determining determines that a low frequency energy falls meets or exceeds a low frequency energy threshold, and wherein the controlling changes the filter parameters of the low-pass filter component to deactivate or decrease a contribution from the low-pass components of the weighted signal.

19. The method according to claim 11 wherein a filter response for the pre-processing weighting filter may be expressed as the following equation:

20. The method according to claim 11 wherein a filter response for the pre-processing weighting filter may be expressed as the following equation:

21. The method according to claim 20 wherein the low-pass adaptive coefficient has a value between 0 and 0.3, γ

₁ falls within a range between 0.9 and 0.97, and γ

₂ falls within a range between 0.4 and 0.6.

22. The method according to claim 19 wherein the low-pass adaptive coefficient has a value between 0 and 0.3, γ

₁ falls within a range between 0.9 and 0.97, and γ

₂ falls within a range between 0.4 and 0.6.

24. The method according to claim 23 wherein the determining comprises determining whether the spectral content of the input speech signal conforms to unwanted background noise or a noisy speech component of an input speech signal.

25. The method according to claim 23 wherein the controlling comprises activating the high-pass filter component in response to the detection of a background noise that meets or exceeds a magnitude level over a certain spectral range.

26. The method according to claim 23 wherein the controlling comprises deactivating the high-pass filter component in response to the detection of a noisy speech component of the input speech signal that meets or exceeds a high frequency energy threshold over a defined spectral range.

27. The method according to claim 23 wherein the controlling comprises changing a filter parameter in response to the detection of the presence or the absence of unwanted noise in the high frequency spectral region of the input speech signal.

28. The method according to claim 23 wherein the determining determines that a high frequency energy falls below a high frequency energy threshold, and wherein the controlling changes the filter parameters of the high-pass filter component to activate or increase the high-pass components filtering of the weighted signal.

29. The method according to claim 23 wherein the determining determines that a high frequency energy falls meets or exceeds a high frequency energy threshold, and wherein the controlling changes the filter parameters of the high-pass filter component to deactivate or decrease the high-pass components of the signal.

30. The method according to claim 23 wherein a filter response for the fixed-codebook weighting filter may be expressed as the following equation:

31. The method according to claim 23 wherein a filter response for the fixed-codebook weighting filter may be expressed as the following equation:

32. The method according to claim 30 wherein the high-pass adaptive coefficient has a value between 0 and 0.5, γ

₁ falls within a range between 0.9 and 0.97, and γ

₂ falls within a range between 0.4 and 0.6.

33. The method according to claim 31 wherein the first adaptive coefficient has a value between 0 and 0.5, γ

₁ falls within a range between 0.9 and 0.97, and γ

₂ falls within a range between 0.4 and 0.6.

35. The encoder according to claim 34 wherein the at least one weighting filter comprises a pre-processing weighting filter and wherein the frequency specific weighting component comprises a low-pass filtering component.

36. The encoder according to claim 35 wherein the controller activates the low-pass filter component in response to the determination that a low frequency energy of the input speech signal falls below a low frequency energy threshold.

37. The encoder according to claim 34 wherein weighting filter comprises a fixed-codebook weighting filter and wherein the frequency specific weighting component comprises a high-pass filtering component.

38. The encoder according to claim 37 wherein the controller activates the high-pass filter component in response to the detection of background noise that meets or exceeds a magnitude level over a certain spectral range.

23. A method for preparing a speech signal for encoding, the method comprising:

determining whether the spectral content of an input speech signal is representative of a noisy speech component;

controlling a high-pass filter component of a fixed codebook weighting filter based on the determination of the spectral content of the speech signal; and

maintaining a core weighting filter component of a fixed codebook weighting filter regardless of the spectral content of the speech signal.

34. An encoder for encoding an input speech signal, the encoder comprising:

a spectral detector for determining whether the spectral content of an input speech signal is representative of a defined spectral characteristic;

at least one weighting filter comprising a core weighting filter component and a frequency specific weighting filter component, the core weighting filter component remaining static regardless of the spectral content of the speech signal;

a controller adapted to control a frequency specific filter component of a weighting filter based on at least one of the determination of the spectral content of the speech signal an affiliation of the weighting filter with a portion of the encoder.