[FieldTrip] ft_preproc_hilbert questions

Rodrigo Montefusco rmontefusco at med.uchile.cl
Tue Oct 28 20:05:33 CET 2014

Hi Max,

to what I understand, the output of Hilbert will be the amplitude of the
input signal (envelope). If you want to use that information, then the only
step you should add before is a very good and sweet narrow band filter (as
narrow as you want your frequency bins). Then, the filter design is the
hard part, because you need a filter that is able to filter out other
frequencies without introducing any kind of artifact.

Hopefully someone else has something to add, or if I'm missing any stuff.



On Tue, Oct 28, 2014 at 2:16 PM, Max Cantor <mcantor at umich.edu> wrote:

> Hi,
> So this is not a specific method-based question, but something more
> general.
> I've been slowly reading through bits and pieces of Mike Cohen's
> 'Analyzing Neural Time Series Data' book, in an attempt to gain a better
> understanding of how things like Fourier Transform, Wavelets, and Hilbert
> work on a more fundamental level.
> Fieldtrip does not have a built in Hilbert time frequency analysis (that
> I'm aware of), but from having read through that chapter of Cohen's book
> I've been able to effectively create a hilbert analysis of my own.
> However, I was wondering if it would be possible to use ft_preproc_hilbert
> (setting cfg.hilbert = 'complex', 'real', etc. in ft_preprocessing) to do
> this in a more efficient and fieldtrip-compatible way. It seems I can use
> this setting to get the analytic signal, phase, power, and other things,
> but since this is on raw/epoched data, there is no obvious way I can think
> of to apply a time or frequency series as in the other TFRs. It seems I
> could either write a fieldtrip function from scratch, which I'm not
> prepared to do, or write a function to reformat fieldtrip data to work
> using the Cohen function, and then output it back into a fieldtrip
> function, which would be fine but I'm more interested to know if the
> ft_preproc_hilbert function can do what I want more efficiently.
> *So boiling it down**, my questions are:*
> 1. Can cfg.hilbert parameter for ft_preprocessing (or ft_preproc_hilbert
> called directly) be used as an ad hoc hilbert TFR, and if so what ad hoc
> steps would one need to take?
> 2. If it cannot be used this way, what situations is it meant for?
> --
> Max Cantor
> Lab Manager
> Computational Neurolinguistics Lab
> University of Michigan
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> fieldtrip at donders.ru.nl
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