[FieldTrip] Wavelet spectrum is cut strangely on low frequencies

[Julian Keil]

Hi Diana,

That is what you would expect given your wavelet settings.
The "strange" cutting off of your low frequencies is due to the length of
the wavelet combined with the length of your trial.
Only frequencies for which your wavelet fits into your trial will be
computed.

For example, 7 cycles at 1 Hz will need 7s of data to compute, 7 cycles at
10 Hz will need 0.7s.

Play around with the cfg.width setting to see the effect of different taper
sizes.

Good luck,

Julian


- Диана <diana-hime at yandex.ru> schrieb am So. 20. Mai 2018 um 17:11:

> Hello!
>
> My name is Diana. Currently I'm triyng to do a wavelet analysis of my
> data, which is 128 (129 with reference elctrode) EEG recording.
>
> The problem is thatthe result looks strangely - the low frequencies are
> cut off. Can't understand the reason for this, and should it be this way or
> it not.  Would be happy with any help)
>
> The script I use:
>
> %preprocessing
> cfg = [];
> cfg.dataset = FileName;
> cfg.continuous   = 'yes'; %считываем файл как непрерывный
> data_preproc = ft_preprocessing(cfg);
>
>
> % deftrial
>  cfg = [];
>   cfg.dataset                 = FileName;
>   cfg.trialdef.eventtype      = 'trigger';
>   cfg.trialdef.eventvalue     = 'tim0';
>   cfg.trialdef.prestim        = 0.2;
>   cfg.trialdef.poststim       = 2.2;
>
>   cfg_deftrial = ft_definetrial(cfg);
>
> data_deftrialed = ft_redefinetrial(cfg_deftrial, data_preproc);
>
> %wavelet
>
>     cfg = [];
>     cfg.channel    = 'all';
>     cfg.method     = 'wavelet';
>        cfg.width      = 7;
>     cfg.output     = 'pow';
>     cfg.foi        = 1:1:45;
>     cfg.toi        = 1:0.01:2;
>     TFRwave = ft_freqanalysis(cfg, data_deftrialed);
>
>
>
>    The wavelet I get:
>
>
>
>
>
> Thanks in advance, Diana.
> Undergraduate Student
> Department of Biology of MSU
>
> P.S: Sorry for my english this time...
> _______________________________________________
> fieldtrip mailing list
> fieldtrip at donders.ru.nl
> https://mailman.science.ru.nl/mailman/listinfo/fieldtrip
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