# fundamental frequency of amplitude data

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Abhijit Sardar on 30 Jan 2021
Commented: Image Analyst on 31 Jan 2021
How can i find fundamental frequency, second and third higher harmonic of the given data?.
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Star Strider on 30 Jan 2021
I have no idea what those variables represent, much less how to assign them to variables.

Image Analyst on 30 Jan 2021
I guess you could take the fft, and the element with the greatest magnitude would be the fundamental frequency, the one at twice the index would be the second harmonic, the element at three times that index would be the energy in the third harmonic, etc. Did you try calling fft() or pwelch()? Do you have any other, different definition of fundamental frequency?
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Image Analyst on 31 Jan 2021
It's the power spectral density. I don't even know what "peak-to-peak amplitude" means. Please define it. To get the amplitude of one peak, or actually of ANY frequency, in the spectrum, you simply look at the value of the array at that frequency. "Peak to peak" is the distance, in units of hertz of the distance between two peaks - it is not an amplitude - it is a frequency difference. If you want the ratio of amplitudes between the PSD at two frequencies, you obviously just take the ratio, like ratio = psdSignal(10)/psdSignal(5), or whatever.