multitapers

[Floris de Lange]

Dear fieldtrippers,

I am experiencing problems when doing a TFR analysis with multitapers.
I have adjusted my t_ftimwin and tapsmofrq to the frequency that is
calculated, as follows:
cfg.t_ftimwin   =
round(TB_TFR_preproc.fsample.*3./cfg.foi)./TB_TFR_preproc.fsample;
cfg.tapsmofrq   =   1./cfg.t_ftimwin;

Since the frequencies I want to look at are between 15 and 50 Hz
(cfg.foi  = 15:50) I get values for the taper time window between 0.2
and 0.06, and for the taper smoothing frequency between 5 and 16.67 Hz.

My signal length is 1.3 sec, which I pad out to 2 sec.
cfg.toi         =   -1:0.02:0.3;
cfg.pad         =   2;

Now, when I do my multitaper analysis, it warns me that there is only 1
taper, for each frequency. I was under the impression that the taper
length is specified by ftimwin, which ranges from 0.2 to 0.06, so I
don't really understand why it only uses one taper.

Can anybody tell me what I'm doing wrong?
Just for completeness, I pasted the settings I use below.

Thanks,
Floris

% with tapers
load TB_TFR_preproc
cfg = [];
cfg.output      =   'pow';
cfg.sgn         =   'all';
cfg.method      =   'mtmconvol';
cfg.foi         =   15:50;

cfg.t_ftimwin   =
round(TB_TFR_preproc.fsample.*3./cfg.foi)./TB_TFR_preproc.fsample;
cfg.tapsmofrq   =   1./cfg.t_ftimwin;
cfg.toi         =   -1:0.02:0.3;
cfg.pad         =   2;
cfg.keeptrials  =   'no';
cfg.keeptapers  =   'no';

TB_mtmconvol=freqanalysis(cfg, TB_TFR_preproc);
save TB_mtmconvol TB_mtmconvol






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