Dear Alfonso,

Thank you for your reply.

Some info regarding the data:
This is a single subject - single session - long functional run (36min, 1350 measurements). It is a optimally combined, but non-denoised multi-echo run (not just concatanated, but combined using T2* combination method). It has undergone default preprocessing with minimal smoothing, but deliberately not denoised as this dataset will be used as a reference to compare several denoising strategies.

The global signal I extracted for the whole timeseries (mean of voxel values) within a mask containing our regions of interest (mostly insula, cingulate cortex, thalamus and brainstem). For future purposes, I would extract global signal whole brain. I used the multitaper method in MATLAB to compute the power spectrum. I suspect the odd constant power spectrum below 0.01Hz might be caused by a too high number of tapers. If I use a more plug&play approach with a MRI quality toolbox I get a power spectrum with a very sharp peak below 0.01Hz.

I double checked the denoising tab and the bandpass setting was definitely at [0.008 inf] (you can even see the improved distribution of connectivity values after denoising). The 'denoising' output is the inputfile with prefix -d
Any idea what I've been doing wrong?

Best regards,
Bram