I'm making an apps that shows spectrum frequency for its features using RealDoubleFFT class from jfftpack. But, I haven't put the scale and unit for the Y axis yet (I've only put scale and unit in X axis that is frequency). What is actually the unit of Y axis (based on the RealDoubleFFT class)? Can anyone help me?
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1The y-axis is the amplitude of the signal. – KillaKem Sep 18 '15 at 16:51
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Amplitude in what unit? dB, volts, or something else? – Dwi Prasetyo Sep 19 '15 at 18:03
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In PCM sample values. Which (you hope) have a linear relationship to signal voltage. Signal power in dBFS will be `20log10(V/VMax)` – marko Sep 19 '15 at 18:05
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I've thinking like that too, but based on the output spektrum by method toTransform[0][i], the output value is between -10 to 10 and i have no idea whats the unit of this value. If i know the unit, i can convert it into other units like db or kind of that – Dwi Prasetyo Sep 19 '15 at 20:28
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Possible duplicate of [Units of a Fourier Transform (FFT) when doing Spectral Analysis of a Signal](http://stackoverflow.com/questions/1523814/units-of-a-fourier-transform-fft-when-doing-spectral-analysis-of-a-signal) – meJustAndrew Nov 27 '16 at 19:45