From help-octave-request at bevo dot che dot wisc dot edu Fri Jan  9 16:13:39 2004
Subject: Re: Frequencies in fir1, etc.
From: Quentin Spencer <qspencer at ieee dot org>
To: help-octave at bevo dot che dot wisc dot edu
Date: Fri, 09 Jan 2004 16:15:12 -0600

Joe Koski wrote:

>For those of us who took our digital signal processing class 20+ years ago,
>is there a simple way to relate w in the call b = fir1(n,w) to an actual
>cutoff frequency (omega sub c or f sub c) based on parameters like point
>spacing (T), n, pi, etc.? Apparently w is between 0 and 1 (at least for a
>low or high pass filter). The conversion must be so trivial that it isn't
>needed, but for me, at least, this conversion would be a useful addition to
>the help files. My 1975 edition of Oppenheim and Schafer isn't too clear on
>this conversion either. Thanks.
>
>Joe Koski
>  
>
The numbers are in the range [0,1], where 1 represents the Nyquist 
frequency, or half the sample rate. In my code, I usually do something 
like this:
f_samp = ( put your sample rate here);
f_nyquist = f_samp/2;
b = fir1(N,[freq_1, freq_2]/f_nyquist);

-Quentin




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