[FieldTrip] EEG preprocessing

[Narayan Iyer]

Hi Jan-Mathijs and David
Thanks for the reply. I will low-pass filter first and the do the down-sampling.Thanks again!
Date: Fri, 11 Jan 2013 09:37:35 +0100
From: jan-mathijs schoffelen <jan.schoffelen at donders.ru.nl>
To: FieldTrip discussion list <fieldtrip at science.ru.nl>
Subject: Re: [FieldTrip] EEG preprocessing
Message-ID: <7A5272B6-AC68-44A3-8003-C5AB3F4F4298 at donders.ru.nl>
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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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