frequency resolution of the power spectrum

[Martin Bleichner]

thanks, I thought there might be an option I could hand over in the cfg.

that will work

2009/7/2 Thomas Hartmann <thomas.hartmann at uni-konstanz.de>

> hi martin,
> the spectral resolution of a fft is determined by the length of the data
> used to calculate it. e.g. a length of 1 second would give a
> frequency-resolution of 1Hz, 2 seconds of data would result in a resolution
> of 0.5Hz and so on....
>
> what you actually missed is that you dont want to calculate one fft on your
> 5-minutes trial but rather several ffts on (overlapping) windows of your 5
> minutes. to do this, refer to the mail by nathan weisz "re: preprocessing
> without trigger...". he shows some code there to cut long trials into
> several short ones. calculate the freqanalysis on these and you will get
> reasonable results.
>
> greez,
> thomas
>
> Martin Bleichner schrieb:
>
>> Hi there,
>>
>> this might be a stupid question. I probably miss something obvious.
>>
>> I want to compute the power spectrum over a single trial (around 5
>> minutes).
>>
>> using this piece of code
>> cfg        = [];
>> cfg.method = 'mtmfft';
>> cfg.output = 'pow';
>> cfg.foilim = [1 100];
>> cfg.taper  = 'hanning';
>> freq       = freqanalysis(cfg, data);
>>
>> as a result I get
>>  freq: [1x62534 double]
>> powspctrm: [96x62534 double]
>>
>> that is a frequency resolution of 0.0032Hz!? What determines the frequency
>> resolution here? What can I do to make it less fine grained?
>>
>> Thanks
>> Martin
>>
>>
>> ----------------------------------
>>
>> The aim of this list is to facilitate the discussion between users of the
>> FieldTrip toolbox, to share experiences and to discuss new ideas for MEG and
>> EEG analysis.
>>
>> http://listserv.surfnet.nl/archives/fieldtrip.html
>>
>> http://www.ru.nl/fcdonders/fieldtrip/
>>
>>
>
> --
> Dipl. Psych. Thomas Hartmann
>
> OBOB-Lab
> University of Konstanz
> Department of Psychology
> P.O. Box D25
> 78457 Konstanz
> Germany
>
> Tel.: +49 (0)7531 88 4612
> Fax: +49 (0)7531-88 4601
> Email: thomas.hartmann at uni-konstanz.de
> Homepage: http://www.uni-konstanz.de/obob
>
> "I am a brain, Watson. The rest of me is a mere appendix. " (Arthur Conan
> Doyle)
>
>
> ----------------------------------
> The aim of this list is to facilitate the discussion between users of the
> FieldTrip  toolbox, to share experiences and to discuss new ideas for MEG
> and EEG analysis. See also
> http://listserv.surfnet.nl/archives/fieldtrip.html and
> http://www.ru.nl/neuroimaging/fieldtrip.
>

----------------------------------
The aim of this list is to facilitate the discussion between users of the FieldTrip  toolbox, to share experiences and to discuss new ideas for MEG and EEG analysis. See also http://listserv.surfnet.nl/archives/fieldtrip.html and http://www.ru.nl/neuroimaging/fieldtrip.
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