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Two microphone auditory sub band adaptive nullforming

Wide band noise reduction is particularly challenging because of the difficulty in isolating one single spatial direction of arrival (DOA) of ambient noise in all frequency bands. It is typical for the DOAs to exhibit a persistent drift with a consequence of degrading the performance of nullforming algorithms. Consider the microphone array topology illustrated in Figure 1 below:

Two Microphone Array

Figure 1: 2 microphone array

where \theta is the DOA of the desired signal. Sub band differential signals can be synthesized as shown in figure 2 below:

 

sub-band adaptive nullforming

Figure 2:  sub-band adaptive nullforming

The delay unit is a function of the separation distance d and the sampling frequency. The outputs of the filter bank could be down sampled depending on the particular implementation.  It can be shown that the optimal weights will satisfy:

W_{opt}(w) = \frac{\mathbb{R}e\{\Phi_{x_1(w),x_2(w)}\} }{\Phi_{x_2(w),x_2(w)}}

where \Phi_{x_i(w),x_j(w)} = \mathbb{E}[x_i(w) x^*_j(w)].

As a custom design house, VOCAL Technologies offers custom designed solutions for blind signal separation with a robust voice activity detector, acoustic echo cancellation and noise suppression. Our custom implementations of such systems are meant to deliver optimum performance for your specific beamforming task. Contact us today to discuss your solution!

VOCAL Technologies, Ltd.
520 Lee Entrance, Suite 202
Amherst New York 14228
Phone: +1-716-688-4675
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Email: sales@vocal.com