[SciPy-user] Re: help for the math-challenged

[Andrew Straw]

John Hunter wrote:

>>>>>> "Andrew" == Andrew Straw <astraw at insightscientific.com> writes:
>
>     Andrew> What is the "critical frequency", as mentioned in the help
>     Andrew> for scipy.signal.iirfilter?  ("Wn -- a scalar or length-2
>     Andrew> sequence giving the critical frequencies.")  More
>     Andrew> specifically, for a 1st order filter, how is the classical
>     Andrew> time constant related to the critical frequency?  By trial
>     Andrew> and error, I find 1.0/(3.19*tau*hz) works.  In other
>     Andrew> words, this is the code I use:
>
> The critical frequency is the frequency at which there is 3dB of
> attenuation of the signal amplitude.  For a first order RC filter,
> this is 1/RC = 1/tau (Hz).

That's what I originally thought (and hence the question).  However, my 
code (which you snipped out) works, which is a state I acheived only 
after I actually playing around with the output.  Therefore, my 
question is not "is my code wrong?", but "why is my code right?".  Then 
again I suppose there could be a bug in scipy and my code actually was 
right! Nah!

Cheers!
Andrew