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Hi everyone,

I am working on Active Noise Cancellation project using NLMS for Headphone. I am
using two microphones. one is for reference signal(x[n]). other one is for error
signal(e[n]). Our system is not cancelling well when testing with white noise.
But cancelling well enough only at 125Hz & 500Hz when testing with mixed
signal(mix of 62.5Hz, 125Hz, 250Hz,.... 8KHz). I am getting the same result when
testing with pure sine wave. Initially I encountered unstable problem. It was
cleared by scaling the reference signal. I am using fixed-point 24-bit DSP,
18-bit ADC & DAC, 16KHz sampling rate. Our system delay is about 720uS. 

Algorithm is functioning well in DSP. I tested it by giving recorded white noise
as a reference input(x[n]) and delayed version of the same as a desired
input(d[n]) and did output & verified the error signal. It is converging
very fast and reducing about 36dB. By doing this i verified my code. But the
same is not working in real time. In real time x[n] and e[n] are the input to
system. Could anyone please answer me the reason for it and also the solution? 

Thanks in advance.

- Jebakumar

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