NEED to design a FIR LPF with cuff frequency at 1 Hz

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suresh
suresh 2012-5-28
fir1(31,0.5) length of the filter is 32 and cuttoff frequency is 1 Hz please some body help me what should be there in place of 0.5

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回答（2 个）

Wayne King
Wayne King 2012-5-28
Nobody can tell you the answer to this question if you do not tell us your sampling frequency.
Solve for Wn in the following
Wn = (2*1)/Fs;
where Fs is your sampling frequency. Then
b = fir1(31,Wn);
You can view the frequency response with:
fvtool(b,1,'Fs',Fs); % again where Fs is your sampling frequency
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suresh
suresh 2012-5-28
sir, my input has sampling period of 30s (for every 30s im getting a sample) then when it is converted into sampling frequency it is 0.03333Hz as per above formula 2*1/ Fs gives me 60 but Wn must be in between 0 to 1

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Wayne King
Wayne King 2012-5-28
The problem is that if you are really sampling only every 30 seconds, then you cannot accurately reproduce data at 1 Hz.
If your sampling frequency is really 0.0333 Hz, then your Nyquist frequency is 0.0333/2 . The highest frequency sine wave you can accurately represent will have a period of 60 seconds, NOT a period of 1 second.

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