Microphone array beamforming

1. A system, comprising:

a microphone array comprising a plurality of microphones positioned at different locations, where the microphones output microphone signals; and

a beamformer that is applied to the microphone output signals and is configured to control a gain that is applied to the microphone output signals, where the gain is frequency dependent and is related to a mismatch in sensitivity between two or more of the microphones, wherein the beamformer is configured to limit the gain that is applied to the microphone output signals at input frequencies below a cutoff frequency of 2000 Hz.

2. The system of claim 1 , wherein the microphones are part of headphones.

3. The system of claim 2 , wherein the headphones comprise an in-ear headset and wherein the microphones are constructed and arranged to detect a sound field that is external to the headset.

4. The system of claim 1 , wherein the beamformer does not limit the gain that is applied to the microphone output signals at input frequencies above the cutoff frequency.

5. The system of claim 1 , wherein the gain contributes to microphone white noise gain, and wherein the limited gain results in a reduction of white noise gain.

6. The system of claim 5 , wherein the white noise gain reduction is at least 4 dB over a range of input frequencies.

7. The system of claim 6 , wherein the range of input frequencies is up to 300 Hz.

8. The system of claim 1 , wherein the beamformer is super-directive.

9. The system of claim 1 , wherein the beamformer is characterized by a plurality of frequency domain coefficients.

10. The system of claim 9 , wherein the frequency domain coefficients are based on at least one of a coherence function of a diffuse noise field and a power spectral density matrix of a non-diffuse noise field.

11. The system of claim 10 , wherein the coherence function is based on microphone sensitivity mismatch parameters of the microphones of the array.

12. The system of claim 11 , wherein the microphone sensitivity mismatch parameters are between approximately 0.1 dB and approximately 0.3 dB.

13. The system of claim 1 , wherein the beamformer is either a near-field beamformer or a far-field beamformer.

14. The system of claim 1 , wherein the beamformer is a minimum variance distortionless response (MVDR) beamformer.

15. The system of claim 1 , wherein the microphone sensitivity mismatch is between approximately 0.1 dB and approximately 0.3 dB.

16. The system of claim 1 , wherein the cutoff frequency is 2000 Hz.

17. The system of claim 4 , wherein the cutoff frequency is 2000 Hz.

18. The system of claim 1 , wherein the cutoff frequency is at least 1000 Hz.

19. A system, comprising:

a microphone array comprising a plurality of microphones positioned at different locations, where the microphones output microphone signals; and

a minimum variance distortionless response (MVDR) beamformer that is applied to the microphone output signals and is configured to control a gain that is applied to the microphone output signals, where the gain is frequency dependent and is related to a mismatch in sensitivity between two or more of the microphones, wherein the beamformer is configured to limit the gain that is applied to the microphone output signals at input frequencies below a cutoff frequency of 2000 Hz, and wherein the beamformer does not limit the gain that is applied to the microphone output signals at input frequencies above the cutoff frequency, wherein the gain contributes to microphone white noise gain, and wherein the reduced gain results in a reduction of white noise gain, wherein the white noise gain reduction is at least 4 dB over input frequencies of up to 300 Hz.