METHOD AND APPARATUS FOR OPTIMIZING DIFFERENTIAL MICROPHONE ARRAY BEAMFORMING
An electronic device may use differential microphone arrays for beamforming. The electronic device may include a first microphone for obtaining a first microphone signal and a second microphone for obtaining a second microphone signal. The electronic device may include a processor to process the microphone signals to obtain frequency bins. The processor may apply delay coefficients to the frequency bins of the microphone signals to obtain a delayed signal. The delay coefficients may be based on a phase difference between the microphone signals. The phase difference may be a function of frequency. The processor may be configured to combine the delayed signal with the first microphone signal or the second microphone signal to obtain a beamformed signal. The electronic device may include a memory to store the beamformed signal.
1 . An image capture device comprising:
a first microphone disposed in an encasement, the first microphone configured to obtain a first microphone signal;
a second microphone disposed in the encasement, the second microphone configured to obtain a second microphone signal;
a processor configured to:
perform a transformation on the second microphone signal to obtain frequency bins;
apply respective delay coefficients to the frequency bins of the second microphone signal to obtain a delayed signal, wherein the respective delay coefficients are based on a measured phase difference between the first microphone signal and the second microphone signal as a function of frequency, wherein the measured phase difference is associated with a deviation caused by the encasement; and
combine the delayed signal and the first microphone signal to obtain a beamformed signal; and
a memory configured to store the beamformed signal.
2 . The image capture device of claim 1 , wherein the respective delay coefficients are variable for each respective frequency bin.
3 . The image capture device of claim 1 , wherein a location of the first microphone relative to a location of the second microphone is such that an effective distance between the first microphone and the second microphone deviates from a true distance between the first microphone and the second microphone.
4 . The image capture device of claim 1 , wherein an average bin width of the frequency bins is configured to match a Fast Fourier Transform (FFT) length.
5 . The image capture device of claim 4 , wherein the FFT length is 256.
6 . The image capture device of claim 4 , wherein the average bin width is approximately 93.75 Hz.
7 . The image capture device of claim 1 , wherein the beamformed signal produces a cardioid polar response, a hypercardioid polar response, or a supercardioid polar response.
8 . A differential microphone array (DMA) beamforming method comprising:
obtaining respective microphone signals from two or more microphones;
performing a transformation on the respective microphone signals to obtain frequency bins;
performing beamforming on the respective microphone signals based on a measured time delay associated with an effective distance between the two or more microphones to obtain beamformed signals;
performing an inverse transformation on the beamformed signals to obtain time domain beamformed signals;
applying gains to the time domain beamformed signals;
encoding the time domain beamformed signals to obtain an encoded stream; and
storing the encoded stream.
9 . The method of claim 8 , wherein performing beamforming further comprises applying respective delay coefficients to the frequency bins of at least one microphone signal of the respective microphone signals.
10 . The method of claim 9 , wherein the respective delay coefficients are variable for each respective frequency bin.
11 . The method of claim 8 , wherein an average bin width of the frequency bins is configured to match a Fast Fourier Transform (FFT) length.
12 . The method of claim 11 , wherein the FFT length is 256.
13 . The method of claim 11 , wherein the average bin width is approximately 93.75 Hz.
14 . The method of claim 11 , wherein the effective distance is based on a measured phase difference between the respective microphone signals.
15 . A differential microphone array (DMA) beamforming method comprising:
obtaining a first microphone signal from a first microphone disposed in an encasement;
obtaining a second microphone signal from a second microphone disposed in the encasement;
performing a transformation on the second microphone signal to obtain frequency bins;
applying respective delay coefficients to the frequency bins of the second microphone signal to obtain a delayed signal, wherein the respective delay coefficients are based on a measured time delay associated with an effective distance between the first microphone and the second microphone and based on a deviation caused by the encasement;
combining the delayed signal and the first microphone signal to obtain a beamformed signal; and
storing the beamformed signal.
16 . The method of claim 15 , wherein the effective distance is based on a measured phase difference between the first microphone signal and the second microphone signal.
17 . The method of claim 15 , wherein the respective delay coefficients are variable for each respective frequency bin.
18 . The method of claim 15 , wherein an average bin width of the frequency bins is configured to match a Fast Fourier Transform (FFT) length.
19 . The method of claim 18 , wherein the FFT length is 256.
20 . The method of claim 18 , wherein the average bin width is approximately 93.75 Hz.