Re: Why is my Butterworth filter so noisy?

[Bob Odom]

Adding some noise to a signal to fill in the frequency "holes" in a
spectrum is a standard technique in signal processing. It is often
referred to as "pre-whitening the data." If you search on this, or look
in a standard book on signal processing you will find lots of examples
and discussion.

Bob

On Wed, 24 Sep 2008, Matthias Brennwald wrote:

> On 23.09.2008, at 21:05, Julius Smith wrote:
>
> > The "noise" in the original post is due to missing frequencies in the
> > input signal, resulting in spurious numerical failures in the spectral
> > ratio Y./X.  If you replace the line
> >
> > x = 2*randn(1,N)-1; % fake time series (original data)
> >
> > by
> >
> > x = [1,zeros(1,N-1)]; % impulse
> >
> > then the response looks fine.  To use noise as an input, it is
> > necessary to do a lot more averaging over time (see the topic of
> > system identification, for example).
> >
> > - jos
>
> Thanks for this! That explains a lot...
>
> Matthias
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