[SciPy-user] Filtering high frquency noise

Travis Brady travis.brady at gmail.com
Tue Mar 21 10:17:39 CST 2006


If you'd like to try out Scipy's capabilities these emails from the
matplotlib list by John Hunter are a good starting point:
http://article.gmane.org/gmane.comp.python.matplotlib.general/3397/match=butterworth
http://article.gmane.org/gmane.comp.python.matplotlib.general/1586/match=butterworth

good luck
Travis

On 3/21/06, lanceboyle at qwest.net <lanceboyle at qwest.net> wrote:
>
> Actually, I think someone did once write a filtering tutorial for
> SciPy but I can't remember who it was or where to find it. Anyway,
> you might look for some of the web sites that have interactive filter
> design capability to get the coefficients that you need, then plug
> them into SciPy's filter routine.
>
> The approach that I would take would be to (1) interpolate the data
> using a cubic spline and then take uniformly-spaced samples at a rate
> that is high enough to guarantee that there is no aliasing (keep
> increasing the sample rate until the spectrum doesn't change), (2)
> low pass filter with the uniform samples, and if necessary (3)
> interpolate the uniform samples to get back the values at the
> original sample instants.
>
> Jerry
>
>
> On Mar 20, 2006, at 2:37 AM, Yannick Dirou wrote:
>
> > Hello,
> >
> > I have a multirate signal (from 18 to 24 sample per day), and if i
> > plot
> > it i see something like "high frequency" noise (actually not that high
> > but higher than the remaining of the signal), i thought about using a
> > median filter but this is not good for a multirate signal,
> > then i though i could use scipy filters to do the job,
> > unfortunately i know nearly nothing in filter design, and don't
> > know how
> > to do the job.
> >
> > Is there a tutorial or simple example to design a low pass filter?
> >
> > the signal data is made of a datetime in epoch format and the measured
> > value.
> >
> > Thanks in advance,
> >
> > Yannick
>
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