Okay, thank you all for your responses.
We found a guitar has its lowest note to 82.4Hz and most acute in 1318.52Hz.
Is it possible to adjust the Fourier analysis for more accurate values between 0Hz and 2000Hz ?
I understood what is the imaginary array. But, what is the third argument, "7"? I know this is 2**7=128 but I do not know what it is.
Thank you !