how to scale fft?
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hy guys.
i have a question concerning the scaling in fft .
i have seen alot of code on this forum, but some of the code scale the fft with length of the time domain while other's with increment.
code:
clear all; clc
dt=0.1;
t=-5:dt:5;
z=numel(t);
df = 1/dt;
f = linspace(-df/2, df/2, z);
h_t=rectpuls(t,1/f0);
h_f=fftshift(fft(h_t,n));
% how to scale h_f? should i divide h_f with z or dt and why?
% thank you in advance
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Matt J
2022-2-10
编辑:Matt J
2022-2-10
The DFT is a tool for computing several other theoretical transforms. It can be used to compute a Discrete Fourier Series, which is when you would scale by the length. It can also be used to approximate a continuous Fourier transform, which is when you scale by the time increment.
There is also some disagreement across different professions (esp., engineering versus physics) on scaling factors in the definitions of these transforms. Therefore, the safest way to determine the scaling that you need is to just compare the formula in Matlab's FFT defintiion to the formula for the thing you want to compute.
8 个评论
Matt J
2022-2-11
No, you must always multiply by dt. The issue of choosing how much zero-padding you need to do is separate.
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