PROBLEM IN DESIGNING A LOW PASS FILTER

Question

raj 2012-3-31

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https://ww2.mathworks.cn/matlabcentral/answers/34096-problem-in-designing-a-low-pass-filter

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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Answer 1

Wayne King 2012-3-31

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https://ww2.mathworks.cn/matlabcentral/answers/34096-problem-in-designing-a-low-pass-filter#answer_42745

在 MATLAB Online 中打开

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);