PROBLEM IN DESIGNING A LOW PASS FILTER
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I have to design a lowpass filter with passband of 0-1000Hz and sampling rate of 10kHz when i implement using fdatool it works but when I use this piece of code there is an error saying 'Value must be strictly positive'. Here is the code please correct me
d = fdesign.lowpass('Fp,Fst,Ap,Ast',0,1000,1,80,10000);
Hd1 = design(d,'equiripple');
t = 0:1e-4:1;
x = cos(2*pi*500*t)+0.5*cos(2*pi*1000*t);
out = filter(Hd1,x);
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Accepted Answer
Wayne King
on 31 Mar 2012
Because Fp is the passband frequency and Fst is the stopband frequency.
You have set your passband frequency to 0.
You cannot have a realizable "brick wall" filter. You must have some transition band between your passband frequency, which for you is 1000 (not 0!), and the stopband frequency.
d = fdesign.lowpass('Fp,Fst,Ap,Ast',1000,1200,1,80,10000);
Hd1 = design(d,'equiripple');
t = 0:1e-4:1;
x = cos(2*pi*500*t)+0.5*cos(2*pi*1000*t);
out = filter(Hd1,x);
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