[Eeglablist] filters

[Tim Schoof]

Hi Makoto,

I got the following response from Clemens Brunner:

Hi Tim,

> I was wondering whether anyone knew the exact filter specifications of
the
> Basic FIR and Short IIR filters implemented in eeglab.

eegfilt() uses firls() or fir1() to compute the filter coefficients for a
given order.

iirfilt() designs an elliptic filter and automatically selects the order
to meet the
filter specs (high cutoff, low cutoff, passband ripple and stopband
attenuation).

> Also - and this is probably a question about filters in general - I was
hoping someone could tell me how to specify a 24 dB/oct roll-off (or I
suppose 12 dB/oct given that the script uses filtfilt). What order would
that correspond to in an FIR filter?

Depends on which filter design technique you use. If you want to go the
manual way,
first pick a design technique (windowing, Kaiser window, optimum filters via
Parks-McClellan, ...), provide the desired specifications, and the
corresponding
parameters (including filter order) will pop out.

You can play around with MATLAB's filter design tools if you have MATLAB
and the
Signal Processing Toolbox. You can use fdesign or filterbuilder, or
fdatool. This
will let you fully customize your filter.

If you want to use such a custom FIR filter with EEGLAB, I guess you would
have to
write a short plugin or filter outside of EEGLAB (i.e. working with EEG.data
directly).

HTH
Clemens

Tim

> Dear Tim,
>
> I'm also interested in knowing this. Arno?
>
> Makoto
>
> 2012/6/4 Tim Schoof <t.schoof at ucl.ac.uk>:
>> Dear eeglab list,
>> I was wondering whether anyone knew the exact filter specifications of the
>> Basic FIR and Short IIR filters implemented in eeglab.
>> Also - and this is probably a question about filters in general - I was
hoping someone could tell me how to specify a 24 dB/oct roll-off (or I
suppose 12 dB/oct given that the script uses filtfilt). What order
would
>> that correspond to in an FIR filter?
>> Many thanks,
>> Tim
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>
> --
> Makoto Miyakoshi
> JSPS Postdoctral Fellow for Research Abroad
> Swartz Center for Computational Neuroscience
> Institute for Neural Computation, University of California San Diego
>