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What are the valid specs for a FIR implementation of a bandstop filter?

Posted 6 years ago
POSTED BY: Guido Fantini
2 Replies

Guido,

The wc term is not in Hz -- it is a number between 0 and Pi, where Pi is Nyquist frequency. You need to decide on the time spacing of your FIR points (your sample rate) and scale wc accordingly. Also, I am surprised that any real application would require an FIR filter of length 10^5 points -- are you certain you need that many points? Typically the filter is a much shorter "Kernel" that gets convolved with a longer time sequence (maybe 10 up to a few hundred points). If you make the FIR very long, while it may be sharper, you suffer a huge time delay. Also, sharp cutoff filters often suffer from ringing in the time domain.

I hope this helps.

Regards

Neil

POSTED BY: Neil Singer
Posted 6 years ago

Thanks for the reply, in the meantime I tried to do the same with Matlab and realized exactly what you said, that indeed to design a notch filter 3 coefficients could be enough. And also that the wc term is

wc = PI * f_cut / f_nyquist = 2*PI * f_cut / f_s

As soon as I get back to mathematica I will try that and eventually post again. Thanks a lot for the reply, that pointed me to the right direction!

Best, Guido

POSTED BY: Guido Fantini
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