# AFNI Message Board

Dear AFNI users-

### https://discuss.afni.nimh.nih.gov

Existing user accounts have been migrated, so returning users can login by requesting a password reset. New users can create accounts, as well, through a standard account creation process. Please note that these setup emails might initially go to spam folders (esp. for NIH users!), so please check those locations in the beginning.

The current Message Board discussion threads have been migrated to the new framework. The current Message Board will remain visible, but read-only, for a little while.

Sincerely, AFNI HQ

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 May 27, 2022 03:28PM Moderator Registered: 10 years ago Posts: 2,321
Hi, Philipp-

I admit I got a bit lost in the description about what the actual question was. Can you please rephrase it directly?

If you are wondering about a factor of 2 difference in a log-plot-based comparison, then I suspect one "power" method is actually calculating magnitude---that is, power is (magnitude)^2, and when you take the log of that, the 2 comes down on the lefthand side:
log(magnitude^2) = 2 log(magnitude).
You are migrating among many software, so it is good to make sure what is being calc'ed in each---first whether it is really power or magnitude (=amplitude), and second that log() is really the consistent base of logarithm you want.

--pt
Subject Author Posted

#### 3dPeriodogram and 1dFFT - How exactly is the power computed?

Philipp May 27, 2022 10:36AM

#### Re: 3dPeriodogram and 1dFFT - How exactly is the power computed?

ptaylor May 27, 2022 03:28PM

#### Re: 3dPeriodogram and 1dFFT - How exactly is the power computed?

Philipp May 27, 2022 03:58PM

#### Re: 3dPeriodogram and 1dFFT - How exactly is the power computed?

ptaylor May 27, 2022 08:52PM

#### Re: 3dPeriodogram and 1dFFT - How exactly is the power computed?

Philipp May 28, 2022 03:36AM

#### Re: 3dPeriodogram and 1dFFT - How exactly is the power computed?

ptaylor May 28, 2022 07:11AM

#### Re: 3dPeriodogram and 1dFFT - How exactly is the power computed?

Philipp May 28, 2022 11:03AM

#### Re: 3dPeriodogram and 1dFFT - How exactly is the power computed?

ptaylor May 31, 2022 05:41PM

#### Re: 3dPeriodogram and 1dFFT - How exactly is the power computed?

Philipp June 01, 2022 12:24AM