Time-domain frequency filter
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I have a set of time-domain data that I wish to filter. I need to use some sort of notch filter so as no delay occurs as a result of the filtering. I only want to use the data with frequencies between 0 and 3 hz to analyse afterwards. The end result must be in the time-domain - I have tried converting to the frequency domain, selecting the appropriate frequencies and then transferring back into the time-domain, which it does not let me do.
How do I perform this procedure totally in the time-domain?
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Accepted Answer
Wayne King
on 16 Apr 2012
An example (requires Signal Processing Toolbox)
d = fdesign.lowpass('Fp,Fst,Ap,Ast',3,4,0.5,50,10);
Hd = design(d);
output = filtfilt(Hd.Numerator,1,inputdata);
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More Answers (3)
Wayne King
on 16 Apr 2012
Sounds like you just need a lowpass filter since you want to only analyze data below 3 Hz. What is your sampling frequency?
You can do what you want by designing your filter using fdesign.lowpass and then using filtfilt() to filter the data.
filtfilt() implements zero-phase filtering and operates in the time domain and returns time-domain data.
Eshwar Sachi
on 3 May 2012
As indicated in the function, 0.5 is the pass band ripple and 50 is the stop band attenuation, in units dB. You may find the following link useful for designing filters in MATLAB: http://www.mathworks.com/discovery/filter-design.html
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