About the fir bandpass filter function; fir1_bp

[Kota]

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Hi,<o:p></o:p>

<o:p> </o:p>

I am very new for signal processing.<o:p></o:p>

I tried to extract the time series signal filtered over the specific range of frequency.<o:p></o:p>

However, the result was different from expected and was time shifted signal.<o:p></o:p>

After the survey, I found the group delay of FIR filter.<o:p></o:p>

And then, I corrected the output of fir1_bp() by using group delay ((N-1)T/2)).<o:p></o:p>

I want to have confidence this procedure.<o:p></o:p>

I am wondering this procedure is ok or not ?<o:p></o:p>

<o:p> </o:p>

Cheers<o:p></o:p>

[Claes Rolen]

Hi, glad you are using Sigpack. The group delay of a linear phase FIR filter, of order N (which gives you N+1 coefficients), is N/2 samples. This means that fir1_bp(8,0.35,0.65) will give a group delay of 4 samples and fir1_bp(9,0.35,0.65) will have 4.5. It mimics the Matlab functions and gives more or less bit exact results. Hope this answers your question, you may Google FIR filter group delay if you want some more details.
// BR Claes