# [FieldTrip] Beamforming analysis in frequency band, concept problem

smoratti at psi.ucm.es smoratti at psi.ucm.es
Tue Mar 27 22:33:36 CEST 2012

```Hi Mikel,

I think Jörn gave you already the answer. You need enough time points to accurately estimate the oscillations of a frequency. For example in wavelet analysis (morlet) people use at least 5 cycles.

Best,

Stephan

________________________________________________________
Stephan Moratti, PhD

Departamento de Psicología Básica I
Campus de Somosaguas
Spain

and

Center for Biomedical Technology
Laboratory for Cognitive and Computational Neuroscience
Campus Montegancedo
Spain

email: smoratti at psi.ucm.es
Tel.:    +34 679219982

El 27/03/2012, a las 12:46, Ion Lavado escribió:

> Thank you Stephan, just one thing, why i need a time window big enough? so i'm just studying the frequency.
>
> Best,
>
> Mikel
>
> 2012/3/27 Stephan Moratti <smoratti at psi.ucm.es>
> Dear Mikel,
>
> I understand that you should do a mtmfft with a center frequency of interest (in your case cfg.foil = [11 11]) and then you do a frequency smoothing of 3 Hz (cfg.tapsmofrq = 3). Of course you need a time window big enough to allow such a smoothing. The CSD should represent a frequency window of 8 to 14 Hz then. Then you put the result of the mtmfft into the dics beamformer.
>
> Best,
>
> Stephan
>
> El 27/03/2012, a las 11:19, Ion Lavado escribió:
>
>> Hello, i'm having problems trying the beamformer analysis with a frequency band of interest. I would like to have for example an interval like [8 14] Hz. My concept problem is about the cfg.frequency and cfg.tapsmofrq  values. (it must be a escalar, but i want a frequency band).
>>
>> %FREQ ANALYSIS
>> cfg = [];
>> cfg.method    = 'mtmfft';
>> cfg.output    = 'powandcsd';
>> cfg.tapsmofrq = 5;
>> cfg.foilim    = [8 14];
>> freq_words_alpha = ft_freqanalysis(cfg, words);
>>
>>
>> %SOURCE ANALYSIS
>> cfg              = [];
>> cfg.frequency    = 11;
>> cfg.lambda=0;
>> cfg.method       = 'dics';
>> cfg.coordsys       = 'neuromag';
>> cfg.projectnoise = 'yes';
>> cfg.channel   = {'MEG'};
>> cfg.grid         = grid;
>> cfg.reducerank      = 2;
>> cfg.vol          = vol02;
>> vol02=ft_convert_units(vol02,'cm');
>> source_pre11  = ft_sourceanalysis(cfg,  freq_words_alpha );
>>
>>
>> I use a cfg.frequency of 11 but i don't have really clear what i'm doing as a get the same result using cfg.frequency=11 but a freqanalysis in [10 12]. I would be very grateful if someone could solve my doubt.
>>
>> Best wishes,
>>
>> Mikel
>> _______________________________________________
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>> fieldtrip at donders.ru.nl
>> http://mailman.science.ru.nl/mailman/listinfo/fieldtrip
>
>
> ________________________________________________________
> Stephan Moratti, PhD
>
>
> Departamento de Psicología Básica I
> Campus de Somosaguas
> 28223 Pozuelo de Alarcón (Madrid)
> Spain
>
> and
>
> Center for Biomedical Technology
> Laboratory for Cognitive and Computational Neuroscience
> Campus Montegancedo
> 28223 Pozuelo de Alarcón (Madrid)
> Spain
>
>
> email: smoratti at psi.ucm.es
> Tel.:    +34 679219982
>
>
>
> _______________________________________________
> fieldtrip mailing list
> fieldtrip at donders.ru.nl
> http://mailman.science.ru.nl/mailman/listinfo/fieldtrip
>
> _______________________________________________
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