# Where do the 219.09 from the abs(fft(x)) come from?

Hello People,
when I have a set of a=csv-files and do a b=fft(abs(a)) and then i do c=b/a with every pair. every c is 219.09.
Can someone explain where the “219.09” come from?

If anything I expected a multiple of sqrt(2).

Is it possible to show an example of the csv file and the whole used code to load the file content and the intended calculations?

here is the csv-file. It is 11MB and I can only upload 8MB.

The code is:

``````c=dlmread("12,5Hz - ausgewaschen - Mkapsel.csv",",",[48000,1,96000,inf]);

absfft=abs(fft(c));

rms1 = (((1 / numel (c)) * (sumsq (c))) .^ 0.5);

rms2 = (((1 / numel (absfft)) * (sumsq (absfft))) .^ 0.5);

x=rms2/rms1;
``````

To clarify my question.
“Why is x 219,09?” At least in all csv-files i have tried.

Maybe the square of 219.09… looks more familiar to you, if you remove all unnecessary scaling operations (those have no effect in the quotient):

``````>> format long
>> (sumsq (absfft) / sumsq (c))
ans = 48001.00000000007
>> (sumsq (absfft) / sumsq (c)) .^ 0.5
ans = 219.0913051675033
``````

Maybe more important to ask, what computation do you wish to do? Looks like your scaling is not properly applied after performing the fft. Is there a formula you want to evaluate?

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