Jerry Avins wrote:

> Tim Wescott wrote:
> 
>> tim w wrote:
> 
> 
>   ...
> 
>>> -Also, the variable "fc" is the corner frequency. What is that on how do
>>> I set it???
>>
>> In a band stop filter fc is the center frequency of the stop band.  In 
>> your transfer function everything is scaled in time, with "To".  For 
>> fc in Hz, fc = 1/(2 * pi * To).
> 
> 
> Other tim,
> 
> Remember to prewarp the critical frequencies. Rick's book goes into it, 
> and so do many other sources. Robert Bristow-Johnson wrote a clear 
> description (in comp.dsp, I think); Google should turn it up. If not, 
> Tim or I can describe the process, the equation is simple.
> 
> Jerry

Check his original URL:  The author has a clever way of building the 
prewarping into the bilinear transform.  Dunno if I'd want to make a 
habit of using it, but it's cute.

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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"Applied Control Theory for Embedded Systems" came out in April.
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