[FieldTrip] 60 Hz notch using preprocessing

[Roemer van der Meij]

Hi Francesco,

Just as a small add to Eelke's reply, you can specify a bs-filter for 
several ranges at once by doing it in a matrix, e.g.:
cfg.bsfreq = [58 62; 118 122];
Note though, these filters (at least the standard butterworth) get 
increasingly inaccurate (less sharp filter-response, more 
'filter-rolling'/edge-artifacts) when going to higher frequencies, if 
you are using the same frequency-range-width.

Best,
Roemer


On 28-10-11 10:36, Eelke Spaak wrote:
> Dear Francesco,
>
> A notch filter is referred to as a band-stop filter in
> ft_preprocessing's documentation, and is different from the
> (regression-based) DFT filter. To use a notch filter, specify:
>
> cfg.bsfilter = 'yes';
> cfg.bsfreq = [58 62]; % or whatever you deem appropriate
>
> Note that you will have to apply ft_preprocessing repeatedly if you
> explicitly want to filter out the harmonics of the line noise as well.
>
> Best,
> Eelke
>
> 2011/10/28 Francesco Di Pompeo<f.dipompeo at unich.it>:
>> Dear all,
>>
>> I need a 60 Hz notch filter before the ICA of continuous 4D data.
>> I did it using ft_preprocessing but the 60 Hz line is still there..
>>
>> Something wrong in my script?
>>
>>
>> cfg = [];
>> cfg.dataset = '0';
>> cfg.channel    = {'MEG', '-A246', '-A170', '-A110', '-A19'};
>>
>> cfg.bpfilter      = 'yes';
>> cfg.bpfreq        = [1 150];
>>
>> cfg.dftfilter     = 'yes';
>> cfg.dftfreq       = [60 120 180];
>>
>> data_meg                 = ft_preprocessing(cfg);
>>
>>
>>
>>
>> -----------------------------------------------------------------
>> Francesco Di Pompeo, PhD
>> Institute of Advanced Biomedical Technologies and
>> Department of Neuroscience and Imaging
>> University of Chieti "G. d'Annunzio"
>> Via dei Vestini - Campus Universitario
>> 66013 Chieti - ITALY
>> ph: +39-0871-3556907
>> fax:+39-0871-3556930
>>
>>
>>
>> _______________________________________________
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>>
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-- 
Roemer van der Meij M.Sc.
PhD student
Donders Institute for Brain, Cognition and Behaviour
Centre for Cognition
P.O. Box 9104
6500 HE Nijmegen
The Netherlands
Tel: +31(0)24 3655932
E-mail: r.vandermeij at donders.ru.nl
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