[Eeglablist] filters

[Makoto Miyakoshi]

Dear Tim and Clemens,

Thanks for feedback.
Since I don't know much about signal processing, my understanding of
filter is the analog one used in an electric circuit with capacitors
and inductors (as used in speakers and amplifiers). Sor it is
intuitive for me, as Tim said, that slope and filter order are such
that 6dB for the first order (1 capacitor/inductor), 12dB for the
second order (capacitor + inductor), 18dB for the third order (3
elements), etc. But it seems filter can be 'designed' pretty freely in
signal processing.

Clemens, I would appreciate if you could show us an introductory
website or paper to learn what is digital filter.

Makoto



2012/6/6 Tim Schoof <t.schoof at ucl.ac.uk>:
> 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
>>
>
>
>



-- 
Makoto Miyakoshi
JSPS Postdoctral Fellow for Research Abroad
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego