Dual omnidirectional microphone array (DOMA)
A dual omnidirectional microphone array noise suppression is described. Compared to conventional arrays and algorithms, which seek to reduce noise by nulling out noise sources, the array of an embodiment is used to form two distinct virtual directional microphones which are configured to have very similar noise responses and very dissimilar speech responses. The only null formed is one used to remove the speech of the user from V 2 . The two virtual microphones may be paired with an adaptive filter algorithm and VAD algorithm to significantly reduce the noise without distorting the speech, significantly improving the SNR of the desired speech over conventional noise suppression systems.
1. A system, comprising:
a microphone array including a first physical microphone outputting a first microphone signal and a second physical microphone outputting a second microphone signal;
a processing component coupled to the microphone array and generating a virtual microphone array including a first virtual microphone and a second virtual microphone, the first virtual microphone including a first combination of the first microphone signal and the second microphone signal, the second virtual microphone including a second combination of the first microphone signal and the second microphone signal, wherein the second combination is different from the first combination, wherein the first virtual microphone and the second virtual microphone have substantially similar responses to noise and substantially dissimilar responses to speech; and
an adaptive noise removal application coupled to the processing component and generating denoised output signals by forming a plurality of combinations of signals output from the first virtual microphone and the second virtual microphone, by filtering and summing the plurality of combinations of signals in the time domain, and by a varying linear transfer function between the plurality of combinations of signals, wherein the denoised output signals include less acoustic noise than acoustic signals received at the microphone array.
2. The system of claim 1 , wherein the acoustic noise comprises noise content and the acoustic signals comprise speech content.
3. The system of claim 2 , wherein the speech content comprises human speech.
4. The system of claim 1 and further comprising: a voice activity detector (VAD) coupled with the processing component and operative to generate voice activity signals.
5. The system of claim 1 and further comprising: a communications channel coupled with the processing component and including one or more of a wireless channel, a wired channel, and a hybrid wireless/wired channel.
6. The system of claim 5 and further comprising: a communication device wirelessly coupled with the wireless channel of the communications channel.
7. A system, comprising:
a first virtual microphone formed from a first combination of a first microphone signal and a second microphone signal, wherein the first microphone signal is generated by a first physical microphone and the second microphone signal is generated by a second physical microphone;
a second virtual microphone formed from a second combination of the first microphone signal and the second microphone signal, wherein the second combination is different from the first combination, wherein the first virtual microphone has a first linear response to speech and first linear response to noise, the first linear response to speech being substantially similar across a plurality of frequencies for a speech source located within a predetermined angle relative to an axis of the microphone array and devoid of a null, wherein the second virtual microphone has a second linear response to speech that has a single null oriented in a direction toward a source of the speech and a second linear response to noise, wherein the second linear response to noise is substantially similar to the first linear response to noise, one or both of the first linear response to noise and the second linear response to noise being non-zero in a direction toward a source of noise, and the second linear response to speech is substantially dissimilar to the first linear response to speech, wherein the speech is human speech; and
an adaptive noise removal application coupled to the first and second virtual microphones and generating denoised output signals by forming a plurality of combinations of signals output from the first virtual microphone and the second virtual microphone, by filtering and summing the plurality of combinations of signals in the time domain, and by a varying linear transfer function between the plurality of combinations of signals, wherein the denoised output signals include less acoustic noise than acoustic signals received at the first and second physical microphones.
8. The system of claim 7 and further comprising:
a microphone array, the first and second physical microphones positioned m the microphone array.
9. The system of claim 7 , wherein the single null is a region of the second linear response to speech having a measured response level that is lower than the measured response level of any other region of the second linear response to speech.
10. The system of claim 7 and further comprising: a voice activity detector (VAD) coupled with the processing component and operative to generate voice activity signals.
11. The system of claim 7 and further comprising: a communications channel coupled with the processing component and including one or more of a wireless channel, a wired channel, and a hybrid wireless/wired channel.
12. The system of claim 11 and further comprising: a communication device wirelessly coupled with the wireless channel of the communications channel.
13. The system of claim 7 , wherein the second microphone signal is multiplied by a ratio, wherein the ratio is a ratio of a third distance to a fourth distance, the third distance being between the first physical microphone and the speech source and the fourth distance being between the second physical microphone and the speech source.
14. A system, comprising:
a first virtual microphone comprising a first combination of a first microphone signal and a second microphone signal, the first virtual microphone having a first linear response to speech and a first linear response to noise, the first linear response to speech being substantially similar across a plurality of frequencies for a speech source located within a predetermined angle relative to an axis of a microphone array, wherein the first microphone signal is output from a first physical microphone and the second microphone signal is output from a second physical microphone;
a second virtual microphone comprising a second combination of the first microphone signal and the second microphone signal, the second virtual microphone having a second linear response to speech and a second linear response to noise, the second linear response to noise being substantially similar to the first linear response to noise, one or both of the first linear response to noise and the second linear response to noise being non-zero in a direction toward a source of noise, and the second linear response to speech being substantially dissimilar to the first linear response to speech, wherein the second combination is different from the first combination, wherein the first virtual microphone and the second virtual microphone are distinct virtual directional microphones; and
a processing component coupled to the first and second virtual microphones, the processing component including an adaptive noise removal application receiving acoustic signals from the first virtual microphone and the second virtual microphone, filtering and summing the acoustic signals in the time domain, applying a varying linear transfer function between the acoustic signals, and generating an output signal, wherein the output signal is a denoised acoustic signal.
15. The system of claim 14 and further comprising: a voice activity detector (VAD) coupled with the processing component and operative to generate voice activity signals.
16. The system of claim 14 and further comprising: a communications channel coupled with the processing component and including one or more of a wireless channel, a wired channel, and a hybrid wireless/wired channel.
17. The system of claim 16 and further comprising: a communication device wirelessly coupled with the wireless channel of the communications channel.
18. The system of claim 14 , wherein the acoustic signals from the first virtual microphone, the second virtual microphone or both are delayed.
19. The system of claim 18 , wherein the delay is raised to a power that is proportional to a time difference between arrival of the speech at the first virtual microphone and arrival of the speech at the second virtual microphone.
20. The system of claim 19 , wherein the power is proportional to a sampling frequency multiplied by a quantity equal to a third distance subtracted from a fourth distance, the third distance being between a first physical microphone and the speech source, the fourth distance being between a second physical microphone and the speech source, and the first and second physical microphones are positioned in the microphone array.