[FieldTrip] A shifting power peak artefact

[Ivaylo Iotchev]

Although, dear Jan (anyone), if I can follow up with a secondary question
to your helpful answer.

Reading the link you offered me I realized it is written with an approach
in mind, which I don't use. I saw on some examples of Fieldtrip scripts on
the official Fieldtrip pages, that you often define the cfg.foi relative to
an unpadded segment, e.g. 0.5 second long time-window is analyzed in steps
of 2 Hz and starting with 2 Hz. Would your text still explain my problem if
I use zero-padding to increase my resolution? More crucially, the position
of the main frequency being 1/segment length behaves as if my padding plays
no role, i.e. the segment length which determines the peak frequency is the
unpadded length.

Finally, only if you have an idea, is the slepian sequence a legit way to
minimize 1/f noise? It seems to flatten the peak, but it also spreads out
the energy, and I wonder if that spread is itself noise or real signal that
was otherwise not visible.

Thank you and sorry if I over-engage you on this one.

Bests,

Ivo

Am Do., 8. Dez. 2022 um 10:04 Uhr schrieb Ivaylo Iotchev <
ivaylo.iotchev at gmail.com>:

> Dankje wel!
>
> Am Do., 8. Dez. 2022 um 10:00 Uhr schrieb Schoffelen, J.M. (Jan Mathijs)
> via fieldtrip <fieldtrip at science.ru.nl>:
>
>> Hi Ivo,
>>
>> See: https://www.fieldtriptoolbox.org/faq/why_largest_peak_spectrum/,
>> and https://www.fieldtriptoolbox.org/faq/why_does_my_tfr_look_strange/
>>
>> Best wishes,
>> Jan-Mathijs
>>
>>
>>
>>
>> On 7 Dec 2022, at 14:40, Ivaylo Iotchev via fieldtrip <
>> fieldtrip at science.ru.nl> wrote:
>>
>> Dear community,
>>
>> I want to rephrase one of my questions without first emphasizing my own
>> theory of what is going on this time... what could cause the largest peak
>> in the data to invariantly be at the frequency which is 1/segment length?
>> That is, the peak is at 2 Hz when the segments are 0.5 seconds long... at 1
>> Hz when the segment is 1 second long etc. ...
>>
>> I previously hypothesized that something might be preventing Fieldtrip
>> from reading the sampling rate out of our data, but feel free to think
>> outside the box I offer you, much appreciated, thanks in advance!
>>
>> Bests,
>>
>> Dr. Ivaylo (Ivo) Iotchev
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