[FieldTrip] mtmconvol with hanning window

[Jochem Rieger]

Hi Dan,

think of short term fft as windowing with a rectangular window. This has 
rather bad frequency resolution (wide central lobe, many side lobes in 
the amplitude spectrum). It produces "veridical" values for the 
amplitude estimate over the analysis  interval (your window length)

The other methods underestimate the amplitudes systematically. If you 
are only interested in relative amplitudes (most cases) that doesn't 
matter.

The Hanning window improves the cross talk and is typically applied 
once  the whole intervall and then an FFT is calculated to get the 
amplitude spectrum. The cost for that improvement is that the amplitude 
estimate are biased towards the center of the window and the amplitude 
values are underestimated.

Multitaper analysis applies multiple orthogonal windows and obtains by 
that approach multilple amplitude spectra, which are then combined for 
the final estimate. Approach reduces the noise in the amplitude 
spectrum  lets  you trade-off frequency resolution against noise.

When you write multiple sliding windows you likely refer to the Welch 
method which applies multiple shorter and partly overlapping tapers to 
the analysis interval and then combines those correlated amplitude 
estimates. This method reduces the noise in the amplitude spectrum. In 
principle, you could use different types of windows.

Hope that helps,

     Jochem


On 27.07.23 18:43, Weisholtz, Daniel S.,MD via fieldtrip wrote:
>
> ACHTUNG!Diese E-Mail kommt von Extern! WARNING! This email originated 
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> Dear FieldTrip community,
>
> I understand that using the hanning window with this function will 
> make this function use a single sliding taper window rather than 
> multitaper. Does that make this analysis equivalent to a short-time 
> fft analysis? If you do this, will FieldTrip ignore the tapsmofrq 
> parameter?
>
> Thanks for your help!
>
> Best,
> Dan
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-- 
Jochem Rieger
Prof. Dr. rer. nat. habil.
Applied Neurocognitive Psychology
DFG Center for Open and Reproducible Neuroscience Tools
NFDI sections ELSA and metadata

Carl-von-Ossietzky University Oldenburg
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