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Sorry for disturb you guys, I've been playing with this the last days. I am computing signals of a wave produced with a wavemaker. Cause I have several sensors (wave gauges) I am sensing the same wave in several places along the canal.

I am cutting each signal into pieces to follow one wave each, this is cause the wave transforms itself along the canal. Due to this I am analyzing pieces of a wave as it moves, lie you can see at the next image:

Image of the three sensors measuring the wave

After this, I've been playing around with the Fourier implementation of wolfram. To know how to plot it and how it works, using this I started to play with Cos[x] and Sin[x] functions. Now I know that the period below needs to be set by me and that after that the peaks of each frequency are shown below as f= 1/A if Sin[A*X].

Whit this info I plotted 2*Sin[Pi*x] and Sin[3*Pi*x], where x is given as a list that goes from 0 to 3.2 in increments of 0.025. That gives us a sampling rate of 40 for each unit (cause .025*40 = 1).

Plotting both as a signal:

Plotting of signals 2*Sin[x] and Sin [3*x]

So our spectrum must show two signals, one at pi/2 and the other at (1/3)*(pi/2) on the x-axis. So far so good and the 1/pi must be larger that is the second one, the 1st one must be shorter... but their amplitudes I can not get them to be honest.

The amplitudes of the 1st one must be shorter as far as I remember, cause it measures the strength of the signal at that frequency and the amplitude of the 1st one (Sin[3*pi*x]) is larger?. Meanwhile, the peak of 2*Sin[pi*x] is shorter?.

Signals plot with their amplitudes after a discrete Fourier transform was applied

Also, their numbers don't match what my intuition tells me, I was expecting the peak of one to be 2 and the other 1, but they have 8 and 6?.

I am sorting ideas of what might be happening, maybe I am getting the peaks wrong, that would explain why the peaks are reversed. Even so, what about the strength of the signal?. I know the Fourier transform is getting the transform of every number, so is scaling? or I am applying this just wrong?.

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