Re: Why is my Butterworth filter so noisy?

[Sergei Steshenko]

--- On Mon, 9/22/08, Matthias Brennwald <address@hidden> wrote:

> From: Matthias Brennwald <address@hidden>
> Subject: Re: Why is my Butterworth filter so noisy?
> To: address@hidden, address@hidden
> Date: Monday, September 22, 2008, 10:27 AM
> On 22.09.2008, at 18:12, Sergei Steshenko wrote:
> 
> > You might be interested in the following:
> >
> >
> http://www.nabble.com/ripple-in-Butterworth-filter-created- 
> >
> by-'butter'-(was-"RE%3A-'long-double'-support--")-
> 
> > td17092962.html#a17092962
> 
> Ok. So THE recommended way of using butter.m is to not
> return the  
> filter coefficients, but the have it return the poles,
> zeros, and the  
> gain. So I'd to the following:
> 
> [z,p,g] = butter (...)
> 
> Now, how should I use z, p and g to filter my data? I
> believe I  
> cannot use filter.m with these data.
> 
> Matthias

There is an example script below the message, it shows how to use poles and
zeros. I mean the

http://www.nabble.com/ripple-in-Butterworth-filter-created-by-'butter'-(was-"RE%3A-'long-double'-support--")-td17092962.html#a17092962
.

Look for

# good accuracy BEGIN 

and for znom (i.e. nominator in z-plane, zeros) and zdenom (denominator
in z-plane, poles) and a couple of 'for' loops - everything is very
straightforward.

Regards,
  Sergei.