time-frequency - zero padding?

Bernhard Spitzer bernhard.spitzer at BCCN-BERLIN.DE
Thu Sep 24 15:27:43 CEST 2009

Dear Fieldtrip experts,

I have a question regarding the cfg.pad settings in frequanalysis.
For TF analysis of my epochs (6s), with a fixed window length
(e.g., 0.4s), i'm using sth like

cfg.output     = 'pow';
cfg.method   = 'mtmconvol';
cfg.taper       = 'hanning';
cfg.foi           = 2.5:2.5:30;
cfg.t_ftimwin = ones(length(cfg.foi),1).*0.4;
cfg.toi           = -0.5:0.05:4;

now I would like to increase the frequency resolution to, say 1Hz,
in order to get a smoother TF map, but keep the data window length
at 400msec. I understand that one can get a higher (interpolated)
frequency resolution by zero padding the data window for fft,
but it is unclear to me how or whether this can be done with
frequanalysis/cfg.pad using a sliding window.

with a sliding window, does cfg.pad add zeros to the windowed
signal (cfg.t_ftimwin), or to the interval specified in cfg.toi, or to
the data epoch ? Can I use cfg.pad to interpolate a higher frequency
resolution for my analysis, or is there another way to do that?

many thanks in advance!


Dr. Bernhard Spitzer
Bernstein Center for Computational Neuroscience
Charité Universitätsmedizin Berlin
Philippstr. 13 House 6
10115 Berlin

Phone: +49 (0)30 2093-6789
Fax: +49 (0)30 2093-6771

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