Single Channel Suppression Of Impulsive Interferences In Noisy Speech Signals

• US 20140095156A1
• Filed: 07/07/2011
• Published: 04/03/2014
• Est. Priority Date: 07/07/2011
• Status: Active Grant

• Current Assignee: Cerence Operating Company (Cerence Inc.)
• Original Assignee: Nuance Communications, Inc. (Microsoft Corporation)
• Inventors: Wolff, Tobias, Hofmann, Christian
• Granted Patent: US 9,858,942 B2
• Time in Patent Office: Days
• US Class Current: 704/226
• CPC Class Codes: G10L 19/025 Detection of transients or attacks for time/frequency resolution switching
• CPC Class Codes: G10L 21/0208 Noise filtering
• CPC Class Codes: H04R 2410/07 Mechanical or electrical reduction of wind noise generated by wind passing a microphone

Abstract

Methods and apparatus for reducing impulsive interferences in a signal, without necessarily ascertaining a pitch frequency in the signal, detect onsets of the impulsive interferences by searching a spectrum of high-energy components for large temporal derivatives that are correlated along frequency and extend from a very low frequency up, possibly to about several kHz. The energies of the impulsive interferences are estimated, and these estimates are used to suppress the impulsive interferences. Optionally, techniques are employed to protect desired speech signals from being corrupted as a result of the suppression of the impulsive interferences.

Claims

1. A method for reducing impulsive interferences in a signal, the method comprising automatically:

identifying a plurality of high-energy components of the signal, wherein energy of each of the plurality of identified high-energy components exceeds a predetermined threshold;

identifying a plurality of temporal derivatives of the plurality of identified high-energy components;

morphologically filtering the identified plurality of temporal derivatives, including detecting onsets of the impulsive interferences and estimating a plurality of interference energies in the signal, based at least in part on the plurality of identified temporal derivatives; and

suppressing portions of the signal, based on the plurality of estimated interference energies.

2. A method according to claim 1, wherein identifying the plurality of high-energy components comprises determining the threshold, such that the threshold is below a spectral envelope of the signal.

3. A method according to claim 1, wherein identifying the plurality of high-energy components comprises determining the threshold, based at least in part on a spectral envelope of the signal and at least in part on a power spectral density of stationary noise in the signal.

4. A method according to claim 3, wherein determining the threshold comprises determining the threshold, such that:

under a first condition, the threshold is a calculated value below the spectral envelope of the signal; and

under a second condition, the threshold is a calculated value above the power spectral density of the stationary noise.

5. A method according to claim 1, wherein:

each of the plurality of identified temporal derivatives is associated with a frequency range; and

the frequency ranges associated with the plurality of identified temporal derivatives collectively form a contiguous range of frequencies beginning below a predetermined frequency.

8. A method according to claim 5, further comprising automatically allowing for gaps in the contiguous range of frequencies, wherein each gap is less than a predetermined size.

10. A method according to claim 1, wherein identifying the plurality of temporal derivatives comprises identifying a region of proximate temporal derivatives in a spectrum of the plurality of identified high-energy components.

11. A method according to claim 1, wherein morphologically filtering the identified plurality of temporal derivatives comprises applying a two-dimensional image filter to the plurality of identified temporal derivatives.

13. A method according to claim 1, wherein estimating the plurality of interference energies comprises initially estimating the interference energies based on a power spectral density of the signal for at least a predetermined period of time and thereafter imposing a temporal monotonic decay on the estimated interference energies.

14. A method according to claim 1, wherein morphologically filtering the identified plurality of temporal derivatives comprises calculating values for a plurality of interference bins, based at least in part on the plurality of estimated interference energies.

15. A method according to claim 14, wherein detecting the onsets of the impulsive interferences comprises detecting the onsets of the impulsive interferences based at least in part on the calculated values for the plurality of interference bins of a previous time frame.

16. A method according to claim 1, further comprising automatically;

determining a starting frequency; and

modifying the plurality of estimated interference energies, so as to enforce a progressively smaller estimated interference energy for progressively higher frequencies, beginning at the determined starting frequency.

17. A method according to claim 16, further comprising automatically:

calculating at least one of a signal-to-interference ratio (SIR) and a total interference-to-noise ratio (INR); and

based on the calculated at least one of the SIR and the INR, adjusting an operational parameter that influences how the plurality of estimated interference energies are modified.

6. (canceled)

7. (canceled)

9. (canceled)

12. (canceled)

18. (canceled)

19. A filter for reducing impulsive interferences in a signal, the filter comprising:

a component identifier configured to identify a plurality of high-energy components of the signal, wherein energy of each of the plurality of identified high-energy components exceeds a predetermined threshold;

a temporal differentiator coupled to the component identifier and configured to identify a plurality of temporal derivatives of the plurality of identified high-energy components;

a morphological filter coupled to the temporal differentiator and configured to detect onsets of the impulsive interferences and estimate a plurality of interference energies in the signal, based at least in part on the plurality of identified temporal derivatives; and

a noise reduction filter coupled to the morphological filter and configured to suppress portions of the signal, based on the plurality of estimated interference energies.

20. A filter according to claim 19, wherein the predetermined threshold is below a spectral envelope of the signal.

21. A filter according to claim 19, wherein the predetermined threshold is based at least in part on a spectral envelope of the signal and at least in part on a power spectral density of stationary noise in the signal.

22. A filter according to claim 21, wherein:

under a first condition, the threshold is a calculated value below the spectral envelope of the signal; and

under a second condition, the threshold is a calculated value above the power spectral density of the stationary noise.

27. A filter according to claim 19, wherein the temporal differentiator is configured to identify the plurality of temporal derivatives, such that each of the plurality of identified temporal derivatives exceeds a predetermined value.

31. A filter according to claim 19, wherein the morphological filter is configured to estimate the plurality of interference energies by initially estimating the interference energies based on a power spectral density of the signal for at least a predetermined period of time and thereafter imposing a temporal monotonic decay on the estimated interference energies.

23. (canceled)

24. (canceled)

25. (canceled)

26. (canceled)

28-30. -30. (canceled)

32-36. -36. (canceled)

37. A computer program product for reducing impulsive interferences in a signal, the computer program product comprising a non-transitory computer-readable medium having computer readable program code stored thereon, the computer readable program including:

program code for identifying a plurality of high-energy components of the signal, wherein energy of each of the plurality of identified high-energy components exceeds a predetermined threshold;

program code for identifying a plurality of temporal derivatives of the plurality of identified high-energy components;

program code for morphologically filtering the identified plurality of temporal derivatives, including detecting onsets of the impulsive interferences and estimating a plurality of interference energies in the signal, based at least in part on the plurality of identified temporal derivatives; and

program code for suppressing portions of the signal, based on the plurality of estimated interference energies.