I have implemented MVDR beamformer for speech signal processing, assuming the gain to be unity for the desired direction(delay vector), but when I am checking it for speech files gain seems to be many folds during speech regions. due to this speech is getting distorted and saturated.I am using 2 mic linear array with separation of 6cm for capturing audio files.
from the problem formulation of MVDR beamforming we assume unit gain in desired direction, do I need to multiply the calculated weights with some small constant(fixed/adaptive)as below in order to control the gain
w = 0.05.*( Inv(noise_cor) * c_ ) / ( ( c_' *Inv(noise_cor )*c_)) ;
or there is some implementation mistake ?
MVDR is adpative beamformer, not fixed beamformer. Preserving undistortion in looking direction cannot guarantee the target speech undistortion, since reverberant noise also comes in that direction, and reverberant speech from other direction will also be suppressed. In all, you should estimate c_ in your code based on the speech_cor.
Dear Arpit Jain,
with the selected separation you placed both microphones practically at the same point of the sound field in a whole voice frequency band (300 Hz to 3400 Hz) .
Hi Arpit,
Assuming that you are using your 2 microphones as a ULA (Uniform Linear Array), the separation of 6cm/0.06m will correspond to a wavelength of 0.12m. Assuming the speed of sound is 343m/s, the wavelength of 0.12m will correspond to a frequency of 2.858 kHz. I am thinking that if your are sampling a audio signal greater than 2.858 kHz, you may want to place the microphones nearer to each other (less than 6 cm, maybe 5 cm for up to 3 kHz) so as to prevent signal returns due to grating lobes from interfering with your intended audio signals.
Also, when using MVDR, an array of 2 elements with only provide two degrees of freedom (DOF) for the constraints: (1) to prevent distortion of the signal in the desired direction of arrival and the (2) to suppress interference from other directions. Thus, by adding a couple more of array elements (microphones), you will be able to produce better interference suppression from undesirable signals from other directions.
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