Method of processing a signal in a hearing instrument, and hearing instrument

1. A method of processing a signal in a hearing instrument, the method comprising the steps of:

calculating a coherence between a plurality of microphone signals or microphone combination signals, wherein the microphone signals or microphone combination signals have different directional characteristics and are measured spatially coincidentally;

determining an attenuation from the coherence; and

applying the attenuation to the signal;

wherein the step of determining the attenuation comprises the sub-steps of calculating, from the coherence, a direct-to-diffuse power ratio, and of determining the attenuation from the direct-to-diffuse power ratio.

2. The method according to claim 1 , wherein the step of determining the attenuation comprises determining an attenuation factor, and wherein applying the attenuation to the signal comprises applying the attenuation factor to the signal.

3. The method according to claim 1 , wherein at least within a range of direct-to-diffuse power ratios the attenuation factor is chosen to be a square root of the ratio of the direct-to-diffuse power ratio and a maximum direct-to-diffuse power ratio value.

4. The method according to claim 1 , wherein at least within a range of coherence values, the attenuation is chosen to be independent of dynamically changing parameters other than the coherence or a plurality of coherence values or a quantity that depends on the coherence or coherence values.

5. The method according to claim 1 , wherein the microphone signals or microphone combination signals are a pressure signal and a pressure difference signal.

6. The method according to claim 5 , wherein the pressure signal is obtained from a pressure microphone and the pressure difference signal is obtained from a pressure difference microphone.

7. The method according to claim 6 , wherein the hearing instrument comprises at least two microphone ports, a pressure difference microphone in communication with at least two of the ports and a pressure microphone in communication with at least one of the ports, wherein the acoustic center of the ports in communication with the pressure microphone is at equal distances from the locations of the ports in communication with the pressure difference microphone.

8. The method according to claim 1 , wherein the step of calculating the coherence is carried out in a plurality of frequency bands and in finite time windows, and wherein the step of applying the attenuation to the signal is carried out in a frequency dependent manner.

9. The method according to claim 8 , wherein the frequency bands are fast Fourier transform bins.

10. The method according to claim 8 , wherein the frequency bands are psychoacoustic frequency bands.

11. The method according to claim 8 , wherein the attenuation in each frequency band is determined to depend on an average of the coherence values over a plurality of frequency bands and/or over a plurality of time frames.

12. The method according to claim 1 , comprising the further step of receiving a further coherence value or quantity that depends on the coherence from another hearing instrument of a binaural hearing instrument system and of determining an average of the coherence or quantity depending thereon and the coherence value or quantity depending thereon.

13. A hearing instrument or hearing instrument system, comprising a plurality of microphones and a signal processor in communication with the microphones, the processor being programmed to carry out a method comprising the steps of:

calculating a coherence between a plurality of microphone signals or microphone combination signals, wherein the microphone signals or microphone combination signals have different directional characteristics and are measured spatially coincidentally;

determining an attenuation from the coherence; and

applying the attenuation to the signal;

wherein the step of determining the attenuation comprises the sub-steps of calculating, from the coherence, a direct-to-diffuse power ratio, and of determining the attenuation from the direct-to-diffuse power ratio.

14. The hearing instrument according to claim 13 , comprising at least two microphone ports, a pressure difference microphone in communication with at least two of the ports, and a pressure microphone in communication with at least one of the ports, wherein the acoustic center of the ports in communication with the pressure microphone is at equal distances from the locations of the ports in communication with the pressure difference microphone.