Filter Design using FIR method question

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Jonathan George
Jonathan George on 30 Apr 2022
Answered: Chandra on 6 May 2022
I'm aware that the window method of FIR filter design samples the time-domain function obtained when an inverse Fourier transform of an ideal 'brickwall' filter is obtained. The samples produced are subsequently truncated (and possibly smoothened) using a window function.
How would I then use this technique for filter design to determine the coefficients of a 14th order low pass filter which has a cutoff frequency of 95Hz using a rectangular window function? The cutoff frequency corresponds to the frequency at which the magnitude of the 'brickwall' filter (from which the filter is derived) transitions from 1 to 0.
The filter is designed to work for signals sampled at 1000Hz.
Additionally, how would I sum the magnitudes of these coefficients? Would sum(x) suffice?

Answers (1)

Chandra
Chandra on 6 May 2022
Hi,
use fir1 function to get the coefficients and use freqz for frequency response or use filter function to filter the signal
The filter order and cut off frequency can be mentioned in fir1.
b = fir1(14,0.00475,'low');% window type can also be represented after the low
you refer to this link for brickwall filter response

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