Re: Frequencies in fir1, etc.

[Joe Koski]

Quentin, 

If I read this correctly, w is simply a fraction (or fractions for band pass
or band stop) of the Nyquist or folding frequency. Fair enough. Thanks.

To whomever: a sentence to this effect in the Octave help files would be
useful for those of us who are MEs, etc. (not EEs) and don't use DSP stuff
every day.  

Joe Koski

on 1/9/04 3:15 PM, Quentin Spencer at address@hidden wrote:

> 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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Octave is freely available under the terms of the GNU GPL.

Octave's home on the web:  http://www.octave.org
How to fund new projects:  http://www.octave.org/funding.html
Subscription information:  http://www.octave.org/archive.html
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