# Re2: [FIELDTRIP] freqanalysis_wltconvol variance

Ingrid Nieuwenhuis ingrid.nieuwenhuis at DONDERS.RU.NL
Mon Aug 17 14:16:48 CEST 2009

```Dear Amr

There is no MEX implementation. I'm quite sure (not 100% though, you could
test with tic toc to be sure) that mtmconvol is faster than wltconvol. I do
have some tips to speed up the analysis though:

1)       make the timesteps smaller, for instance 0.05 sec in stead of 0.01
sec. You have a time window of 0.5 second, so your actual time resolution is
quite limited anyway.

2)       Do you really need a frequency resolution of 2 Hz? You could start
with 5 Hz frequency steps and increase the resolution if needed later.

Hope this helps a bit,

Ingrid

PS please don't put my name above the question so also others can feel free
to answer the question. I don't mind answering questions (if they are well
phrased and I happen to know the answer such as in your case :-)), but I
also don't mind if others do ;-)

_____

From: FieldTrip discussion list [mailto:FIELDTRIP at NIC.SURFNET.NL] On Behalf
Of Amr Ayoub
Sent: Monday, August 17, 2009 1:38 PM
To: FIELDTRIP at NIC.SURFNET.NL
Subject: [FIELDTRIP] Re2: [FIELDTRIP] freqanalysis_wltconvol variance

Dear Ingrid,

The analysis is painfully slow; it would need weeks to finish. Is there a
MEX implementation of the time freq. analysis? Which is faster wltconvol or
mtmconvol?
Below is the configuration of the time freq. analysis.

cfg.sgn          = 'MEG';
cfg.method       = 'mtmconvol';
cfg.output        = 'pow';
cfg.foi          = 40:2:100 ;
cfg.toi          = -1.4:0.01:1.4;
cfg.keeptrials='yes';
cfg.t_ftimwin    = ones(length(cfg.foi),1).*0.5;   % length of time
window = 0.5 sec
cfg.taper        = 'hanning';
TFR = freqanalysis(cfg, TFA_slo_fz);

vs

cfg.sgn          = 'MEG';
cfg.method       = 'wltconvol ';
cfg.width        = 7;
cfg.output        = 'pow';
cfg.foi          = 40:2:100 ;
cfg.toi          = -1.4:0.01:1.4;
cfg.keeptrials='yes';
TFR = freqanalysis(cfg, TFA_slo_fz);

Data configuration:
Number of channels:151
Sampling rate:250
Number of trials:391

PC configuration: Windows Vista Business SP1 64 bit - Intel Core 2 CPU 6320
@ 1.86Ghz  1.86Ghz - RAM 4GB

Best regards,
Amr

_____

From: Ingrid Nieuwenhuis <ingrid.nieuwenhuis at DONDERS.RU.NL>
To: FIELDTRIP at NIC.SURFNET.NL
Sent: Thursday, August 6, 2009 2:26:28 PM
Subject: Re: [FIELDTRIP] freqanalysis_wltconvol variance

Dear Amr,

If you do freqanalysis with cfg.keeptrials = 'yes', you get the power per
trial. If you subsequently use freqdescriptives (see help for detailed
options) you can compute the variance over trials.

Best Ingrid

_____

From: FieldTrip discussion list [mailto:FIELDTRIP at NIC.SURFNET.NL] On Behalf
Of Amr Ayoub
Sent: Thursday, August 06, 2009 1:56 PM
To: FIELDTRIP at NIC.SURFNET.NL
Subject: [FIELDTRIP] freqanalysis_wltconvol variance

Hello,

I am expecting that you are averaging the power spectrum across the trials
in freqanalysis_wltconvol. Is there a way to compute the variance across the
number of trials?

Amr Ayoub

----------------------------------

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/

----------------------------------

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/

----------------------------------

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/

----------------------------------
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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