need help in these Flter Questions

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vjfaisal

Full Member level 4
firpmord ripple calculate dev

hi

i have got some problem here during designing of band pass filter
using optimal and kaiser(window).
The statement is from documents of kaiserord
Results are inaccurate if the cutoff frequencies are near 0 or the

Nyquist frequency, or if dev is large (greater than 10%).

Q1: what the DEV meant for? and what this (greater than 10%) means,

which causes to inaccurate the results

The statement from the kaiserord document in Matlab

You specify each entry in dev as a positive number, representing

absolute filter gain (not in decibels)

Q2: what does the satement try to tell? please expain in detail

best regards

hi ,
here is the code for the equiripple filter

rp = 3; % Passband ripple
rs = 40; % Stopband ripple
fs = 2000; % Sampling frequency
f = [500 600]; % Cutoff frequencies
a = [1 0]; % Desired amplitudes
% Compute deviations
dev = [(10^(rp/20)-1)/(10^(rp/20)+1) 10^(-rs/20)]; <<<<<
[n,fo,ao,w] = firpmord(f,a,dev,fs);
b = firpm(n,fo,ao,w);
freqz(b,1,1024,fs);
title('Lowpass Filter Designed to Specifications');

Q1: As we already give a[1 0 ] ,showing our desired Amplitude (passband), then why in the firpmod , it could itself calculate the Amplitudes in ao.

Q2: why here both the stop and pass Ripples are divide for the desired Amplitude?

best regards

vjfaisal

Full Member level 4
firpmord ripple dev