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Topic: zero phase low pass filter - filtfilt and IFIR
Replies: 9   Last Post: May 15, 2013 4:25 AM

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stefano Mangione

Posts: 36
Registered: 9/12/09
Re: zero phase low pass filter - filtfilt and IFIR
Posted: Sep 12, 2009 8:28 AM
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What do you mean by zero-phase? Zero group delay in the passband maybe? Try a Butterworth design, it will have a small frequency-dependent group delay in the passband (ad a large delay in the transition band). A linear phase FIR design has a group delay about half of the filter length, so if delay is important you must use a low-order filter.

"Hans " <> wrote in message <h8fh19$l2m$>...
> I'm looking for how to build a zero phase low pass filte. For example:
> h = fdesign.lowpass(Fpass, Fstop, Apass, Astop, Fs);
> Hd = design(h, 'ifir');
> do a good job to easily create a filter operator, that works fine with filter. But there is a big offset when I use the "filter" command.
> y = filter(Hd,time-series-data);
> "filtfilt" ....
> would avoid this offset, but doesn't like this filter operator.
> So my question is how, create as easily such a low pass filter operator, accepted by "filtfilt" or how to create otherwise a zero phase low pass filter ?
> hans

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