Re: Frequencies in fir1, etc.

[Quentin Spencer]

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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