Re: Slow varying inputs

On Sun, 2005-03-06 at 22:26 -0500, Daniel Nilsson wrote:
> On Sun, Mar 06, 2005 at 10:07:06PM -0500, Sandy Pond wrote:
> > On Sun, 2005-03-06 at 18:32 -0500, Daniel Nilsson wrote:
> > 
> > > I've been playing with different kinds of filters to compare
> > > performance, while doing so I found that I could create an IIR filter
> > > with a relatively small order (4 for example) that would act as a very
> > > efficient low-pass filter. To get the same characteristics using an
> > > FIR filter I had to create a much higer order (>30), this makes sense
> > > to me. Correct me if I'm wrong...
> > 
> > Although your question wasn't directed to me I suggest you try comparing
> > to a 4 order of the low_pass_filter.c I posted before.
> 
> Didn't really intend to make it directed actually, your answers are
> very welcome !
> 
> > I attached an example2_low_pass_filter.c which uses 4 poles.
> 
> Thanks, I have been looking at your code trying to figure out if you
> are implementing an FIR or IIR filter ? Or is it some other kind of
> filter ? Sorry for the basic questions here...
> 
> I found some free FIR filter implementations in C as well if anyone
> else following this thread is interested:
> 
> http://www.dspguru.com/sw/opendsp/alglib.htm
> 
> > > From reading various FAQs I find that one of the concerns with IIR
> > > filter over FIR filters is stability. Would that be a concern in an
> > > application where I use samples from Comedi ?
> > > 
> > 
> > Since the low_pass_filter.c has no zeros it's always stable and
> > guarantied to have unity steady state gain.  The code is very efficient
> > as well.
> 
> That sounds good, I'll give your code a try. I'm been working in
> octave to filter my samples (hacked up one of the comedi demos
> to just dump the data in a format that can be read into octave). I
> can't figure out from you code how to extract the A and B filter
> coefficients though so that I can run my samples using your filter
> using the filter and freqz functions in octave (or Matlab) ?
> 
> Thanks

Sorry for the noise.  I forgot to attach the 4-order example.  I've
really got to go to bed :)