[FieldTrip] DPSS and montage

Casper van Heck caspervanheck at gmail.com
Wed Oct 12 11:40:57 CEST 2011


Dear fieldtrippers,

I've been using Fieldtrip as an Intern for two months now, and have
repeatedly run into a problem when using DPSS. When using the below
settings, the computer locks up within seconds (although it does seem to do
'something'), stays that way for up to ten minutes (which is my personal
cutoff, where I force a reboot), and then reports an 'out of memory'.

cfg.method = 'mtmfft';
cfg.output = 'pow';
cfg.taper = 'dpss';
cfg.foilim = [20 200];
cfg.tapsmofrq = 1;

The data fed to ft_freqanalysis is the result of roughly 30 seconds
continuous data of a single (originally bipolar) channel processed by
ft_preprocessing.
When using 'hanning' it completes without a hitch, but DPSS doesn't. I've
tried the same thing using a different, more powerful computer, which
succesfully completed 30 seconds using the above settings, but when setting
the tapsmofrq to 3 the RAM was filled up in a period of a few seconds, and
the computer choked. The 'normal' computer has 2GB of ram, and a dual-core
intel running at 2GHz, and the more powerful computer has 8GB ram with an
quad-core AMD at 3.4GHz. What am I doing wrong?

Secondly, I was wondering about the 'montage' funcionality, since I'll be
making use of bipolar arrangements, but the parameters of the
montage-structure as defined on
http://fieldtrip.fcdonders.nl/reference/ft_apply_montage don't help me much
in making one of my own. Would it be possible to take a look at an existing
montage structure, such as the one referred to on
http://fieldtrip.fcdonders.nl/getting_started/neuralynx_fcdc?

Sincerely,

Casper van Heck
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