[FieldTrip] EEG preprocessing

[jan-mathijs schoffelen]

Hi Subbu,

To follow up on David's reply: when you use the ft_resampledata function, the data is also automatically low-passfiltered to avoid aliasing.
Highpass filtering is not necessary to avoid aliasing, but in general helps to make the data better behaved at the edges, which avoids ringing of the low-pass filter.



Best,

Jan-Mathijs

On Jan 11, 2013, at 4:36 AM, David Groppe wrote:

> You need to low-pass filter the data before downsaple to avoid aliasing.
> The matlab function decimate.m can do this for you.
>   cheers,
>     -David
> 
> On Thu, Jan 10, 2013 at 3:22 PM, Narayan Iyer <eeguser at hotmail.com> wrote:
>> Hi
>> 
>> I have a question on EEG preprocessing. The sampling rate of my 64 channel
>> EEG data is 500 Hz and I would like to down-sample this to 256 Hz or 128 Hz.
>> My question is, i it advisable to low-pass filter the data first (70 Hz) and
>> then down-sample  followed by high-pass filter (0.5 Hz) to avoid aliasing
>> effect  or should I down-sample first and then band-pass filter the data
>> (0.5-70 Hz) ? Or does the sequence really matter ?
>> I am new to EEG data analysis so this question might be really basic, but
>> any help is highly appreciated!
>> 
>> Thanks
>> Subbu
>> 
>> _______________________________________________
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>> fieldtrip at donders.ru.nl
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> 
> 
> 
> -- 
> David Groppe, Ph.D.
> Postdoctoral Researcher
> North Shore LIJ Health System
> New Hyde Park, New York
> http://www.cogsci.ucsd.edu/~dgroppe/
> _______________________________________________
> fieldtrip mailing list
> fieldtrip at donders.ru.nl
> http://mailman.science.ru.nl/mailman/listinfo/fieldtrip

Jan-Mathijs Schoffelen, MD PhD 

Donders Institute for Brain, Cognition and Behaviour, 
Centre for Cognitive Neuroimaging,
Radboud University Nijmegen, The Netherlands

Max Planck Institute for Psycholinguistics,
Nijmegen, The Netherlands

J.Schoffelen at donders.ru.nl
Telephone: +31-24-3614793

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