Noise suppressor for removing irregular noise

• US 20080052067A1
• Filed: 05/31/2007
• Published: 02/28/2008
• Est. Priority Date: 08/25/2006
• Status: Active Grant

• Current Assignee: OKI Electric Industry Company Limited
• Original Assignee: OKI Electric Industry Company Limited
• Inventors: Morito, Makoto
• Granted Patent: US 7,917,359 B2
• Time in Patent Office: Days
• US Class Current: 704/226
• CPC Class Codes: G10L 21/0208 Noise filtering

Abstract

A noise suppressor detects a peak position in the frequency spectrum of an input speech signal, and masks frequency components in the spectrum as a function of the peak position. The masking process attenuates or removes frequency components near the peak position if their magnitudes are significantly lower than the magnitude of the spectrum at the peak position. This noise suppressor effectively removes irregular noise from the spectrum while leaving enough of the spectrum to reproduce the speech signal clearly.

Claims

1. A noise suppressor for removing noise components from a speech signal, comprising:

a peak detector for detecting a peak position in a spectrum of the speech signal; and

a masking processor for reducing components of the spectrum as a function of the peak position, thereby generating a noise-suppressed spectrum.

2. The noise suppressor of claim 1, further comprising a frequency analyzer for receiving the speech signal and obtaining the spectrum of the speech signal.

3. The noise suppressor of claim 1, further comprising a signal generating processor for converting the noise-suppressed spectrum to an output speech signal.

4. The noise suppressor of claim 1, wherein the peak detector detects the peak position by making a sliding comparison of the spectrum with a local comparison function.

5. The noise suppressor of claim 4, wherein the peak detector calculates a dissimilarity value for different positions in the spectrum, the dissimilarity value indicating a degree of dissimilarity between the local comparison function and a local part of the spectrum, and detects the peak position as a position at which the dissimilarity value attains a local minimum value lower than a predetermined threshold.

6. The noise suppressor of claim 1, wherein the masking processor reduces said components to zero.

7. The noise suppressor of claim 1, wherein the masking processor attenuates said components.

8. The noise suppressor of claim 1, wherein for each component of the spectrum, the masking processor obtains a masking value as a function of the peak position, a magnitude of the spectrum at the peak position, and a frequency number, and reduces the component if the component has a magnitude satisfying a predetermined condition with respect to the masking value.

9. The noise suppressor of claim 8, wherein the predetermined condition is that the magnitude of the component is less than the magnitude of the spectrum at the peak position by at least the masking value.

10. The noise suppressor of claim 9, wherein the masking value is constant within a local range including the peak position, and only components within the local range are reduced.

11. The noise suppressor of claim 9, wherein the masking value is a sum of a first function of the peak position and the frequency number and a second function of the magnitude of the spectrum at the peak position.

12. A method of removing noise components from a speech signal, comprising:

detecting a peak position in a spectrum of the speech signal; and

reducing components of the spectrum as a function of the peak position, thereby generating a noise-suppressed spectrum.

13. The method of claim 12, further comprising receiving the speech signal and obtaining the spectrum of the speech signal.

14. The method of claim 12, further comprising converting the noise-suppressed spectrum to an output speech signal.

15. The method of claim 12, wherein detecting the peak position further comprises making a sliding comparison of the spectrum with a local comparison function.

16. The method of claim 12, wherein reducing components of the spectrum further comprises:

obtaining a masking value as a function of the peak position, a magnitude of the spectrum at the peak position, and a position of a component of the spectrum; and

reducing the component if the component has a magnitude satisfying a predetermined condition with respect to the masking value.

17. The method of claim 16, wherein the predetermined condition is that the magnitude of the component is less than the magnitude of the spectrum at the peak position by at least the masking value.

18. The method of claim 17, wherein the masking value is constant within a local range including the peak position, and only components within the local range are reduced.

19. A machine-readable medium storing instructions executable by a computing device to remove noise components from a speech signal, the instructions comprising:

instructions for detecting a peak position in a spectrum of the speech signal; and

instructions for reducing components of the spectrum as a function of the peak position, thereby generating a noise-suppressed spectrum.