# How to turn the internal sound note into the form of function

I want to make a brief Fourier transformation of the sound notes of the same pitch but played by different instruments to see the difference of their Fourier patterns. But I can't find any example of showing SoundNote in the function form or any similar operation in the Documentation Center.

So I hope someone could help me on this. Thank you in advance, sincerely.

I'm not entirely sure what you mean by "showing SoundNote in the function form", but if you want a list of audio samples corresponding to a SoundNote[], use AudioData[]:
dat = AudioData[SoundNote["C", 1, "Marimba"]];

ListLinePlot[Log10[Abs[Fourier[#]]^2] & /@ dat]