[Eeglablist] filters

[Arnaud Delorme]

Dear Makoto, Clemens and Tim,

in EEGLAB 11, you can plot the FIR and IIR filter frequency and phase response.  Looking at the filter response, you can figure out everything you need to know 
about the filter. Hope this helps,

Arno

On Jun 6, 2012, at 11:29 PM, Makoto Miyakoshi wrote:

> Thanks Clemens!
> 
> Makoto
> 
> 2012/6/6 Clemens Brunner <clbrunner at ucsd.edu>:
>> Makoto, it's the other way round for me -- I'm not an expert in analog
>> filter design, but I do know a little bit about signal processing :-). Yes,
>> your intuition is correct. You can still apply this to digital filters --
>> IIR filters are typically designed using analog design technique and then
>> transferring that to the digital domain. FIR filters are usually
>> digital-only, so I'm not sure if these properties apply (of course, if you
>> increase the filter order of an FIR filter, the cutoff will be steeper, but
>> I cannot tell you if there is a way to determine the slope).
>> 
>> There is a good introductory paper by the Mathworks, which talks about
>> filters and has MATLAB examples:
>> http://www.mathworks.com/tagteam/55876_digfilt.pdf
>> 
>> HTH
>> Clemens
>> 
>> 
>> 
>> On 06/06/2012 11:28 AM, Makoto Miyakoshi wrote:
>>> 
>>> 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
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