[FieldTrip] Sharp transition in multitaper coherence when moving from one taper to two

Mircea Stoica m.stoica at uke.de
Wed Oct 11 21:54:41 CEST 2017

Dear fieldtrippers,

I'm interested in coherence analysis with mtmconvol and multitapers. My
frequencies of interest are spaced logarithmically (steps of 1/16 octaves)
and I adjust the time window and number of tapers to yield a constant
frequency smoothing of 0.75 octaves (half that for cfg.tapsmofrq of
course). This results in an ugly step-like transition of coherence when
moving from one taper to two, as you can see in the following image.


This sharp transition is not visible in the power output. I calculated the
actual frequency smoothing as fw = (K + 1) ./ cfg.t_ftimwin / 2 and in a
semilogy plot it gives this:


And the number of tapers for each frequency:


There are no discontinuities in the frequency smoothing. Any ideas what
could be the cause? Or is there perhaps nothing to be done about it?



Universitätsklinikum Hamburg-Eppendorf; Körperschaft des öffentlichen Rechts; Gerichtsstand: Hamburg | www.uke.de
Vorstandsmitglieder: Prof. Dr. Burkhard Göke (Vorsitzender), Prof. Dr. Dr. Uwe Koch-Gromus, Joachim Prölß, Martina Saurin (komm.)

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