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!
Bernhard


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

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

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

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