Back to the main page.

Bug 225 - what's the effect of slow drifts in my data on my spectral decomposition?

Reported 2010-11-18 09:59:00 +0100
Modified 2011-07-06 16:38:12 +0200
Product: FieldTrip
Component: core
Version: unspecified
Hardware: PC
Operating System: Mac OS
Importance: P1 normal
Assigned to: Jan-Mathijs Schoffelen
Depends on:
See also:

Jan-Mathijs Schoffelen - 2010-11-18 09:59:07 +0100

A fundamental feature of spectral analysis (when using tapers to control for spectral leakage) is that the basis functions are not strictly orthogonal. In particular the low frequencies (DC + ) present in the data can as a consequence leak to the whole spectral range. As this may be an unwanted outcome of the spectral analysis, it is generally best to mean subtract/detrend/highpassfilter the time domain data prior to the spectral decomposition. After a discussion with Robert we decided not to let the user be responsible for this, but build it into fieldtrip. More specifically, at the level of the low-level specest functions we will implement this as 'detrend' 0/1/2, which will fit and subtract a 0/1/2 order polynome to the time series. The higher level calling function will set the default (did we agree to let ft_freqanalysis put it to 2?). Additionally, we will write some documentation in the form of a FAQ, similar to one already existing FAQ related to the TFR and DC.