Noise suppression based on null coherence
View Patent ↗Noise suppression is performed based on null coherence between sub-band signals of a primary acoustic signal and a secondary acoustic signal. The null coherence of a signal refers to portions of the signal that have high coherence and can be nullified by a null processor. The nullified component corresponds to target sources, such as an individual speaking into a phone. The coherence values indicate the presence of a target source and are used to suppress noise in portions of a signal that are not dominated by a desired target source. The inter-microphone level difference may be used in combination with the null coherence to provide noise suppression.
1. A method for reducing noise within an acoustic signal, the method comprising:
receiving a first acoustic signal and a second acoustic signal;
determining an energy level of a noise component in the first acoustic signal based on a spatial null in a desired direction and a coherence between the first and second acoustic signals; and
applying a signal modification to the first acoustic signal to reduce the energy level of the noise component, the signal modification based on the determined energy level of the noise component.
2. The method of claim 1 , wherein the coherence is a measurement between the first acoustic signal and an output of a spatial processor.
3. The method of claim 2 , further comprising determining a signal to noise ratio between the first acoustic signal and the output of the spatial processor.
4. The method of claim 3 , wherein null coherence is a ratio of the energy level of the first acoustic signal and the energy level of a null signal.
5. The method of claim 3 , wherein null coherence is a ratio of the energy level of the combination of the first acoustic signal and the second acoustic signal and the energy level of the output of a null processor.
6. The method of claim 1 , further comprising separating the first acoustic signal into a plurality of first acoustic sub-band signals and separating the second acoustic signal into a plurality of second acoustic sub-band signals, and wherein determining the energy level of the noise component and applying the signal modification are on a per sub-band signal basis for the first and second plurality of acoustic sub-band signals.
7. The method of claim 1 , wherein determining the energy level of the noise component in the first acoustic signal is further based on an energy level difference between the first and second acoustic signals.
8. The method of claim 1 , wherein the signal modification is determined at least in part based on an inter-microphone level difference between the first acoustic signal and the second acoustic signal.
9. The method of claim 1 , further comprising:
determining a signal to noise ratio based on the null coherence; and
determining the signal modification at least in part on the signal to noise ratio.
10. A non-transitory computer readable storage medium having embodied thereon a program, the program being executable by a processor to perform a method for processing an audio signal, the method comprising:
receiving a first acoustic signal and a second acoustic signal;
determining an energy level of a noise component in the first acoustic signal based on a spatial null in a desired direction and a coherence between the first and second acoustic signals;
and applying a signal modification to the first acoustic signal to reduce the energy level of the noise component, the signal modification based on the determined energy level of the noise component.
11. The non-transitory computer readable storage medium of claim 10 , wherein the coherence is a measurement between the first acoustic signal and an output of a null coherence module.
12. The non-transitory computer readable storage medium of claim 11 , further comprising determining a signal to noise ratio between the first acoustic signal and the output of the null coherence module.
13. The non-transitory computer readable storage medium of claim 12 , wherein null coherence is a ratio of the energy level of the first acoustic signal and the energy level of a null signal.
14. The non-transitory computer readable storage medium of claim 12 , wherein null coherence is a ratio of the energy level of the combination of the first reference signal and the second reference signal and the energy level of the combination of the first and second acoustic signals.
15. The non-transitory computer readable storage medium of claim 10 , the method further comprising separating the first acoustic signal into a plurality of first acoustic sub-band signals and separating the second acoustic signal into a plurality of second acoustic sub-band signals, and wherein determining the energy level of the noise component and applying the signal modification are on a per sub-band signal basis for the first and second plurality of acoustic sub-band signals.
16. The non-transitory computer readable storage medium of claim 10 , wherein determining the energy level of the noise component in the first acoustic signal is further based on an energy level difference between the first and second acoustic signals.
17. The non-transitory computer readable storage medium of claim 10 , wherein the signal modification is determined at least in part based on an inter-microphone level difference between the first acoustic signal and the second acoustic signal.
18. The non-transitory computer readable storage medium of claim 10 , the method further comprising:
determining a signal to noise ratio based on the null coherence; and
determining the signal modification at least in part on the signal to noise ratio.