What is the difference between a note and a song as seen by fast fourier transform?

A song is a sequence of notes... but a note is a superposition of a fundamental frequency and its harmonics. Suuposing you give MATLAB a recorded note of music, that is non uniform and has a non repeating waveform. When I performed fft of that note, I got one frequency peak. When I performed fft of a song which I had recorded on a keyboard, I got many frequency peaks, and one highest frequency. So, how does MATLAB distinguish between a note and a song? And what is the relevance of a peak frequency in a song?

[Samyukta Ramnath]

To clarify, I played the entire song on the same instrument. So, how does MATLAB distinguish between a note and a song on a single instrument?

[Azzi Abdelmalek]

Why are you comparing a note with a song?, you can have a sound with one note. You can't distinguish between a note and a sound, because this sound is composed by those notes

Answer 1

[Image Analyst]

A note will probably include one type of instrument or sound and thus have a narrower spectrum than the entire song which will contain a much wider variety of instruments and sounds. A piccolo note is narrow and lives in a higher part of the spectrum than a tuba, which may be narrow also but lives in the lower part of the spectrum. Throw in a whole band or orchestra and you have frequencies all over the place and thus the spectrum will be wider and quite different than a single note from a single instrument.

Answer 2

[Azzi Abdelmalek]

I think it's complicated, when you play a song with multiple instruments, one note can be played at several fundamental frequencies. The note Do (C) for example can be played at the below fundamental frequencies (Hz) 32.70 65.41 130.81 261.63 523.25 1046.50 2093.00 4186.01. ....

Re has its own frequencies which is related to the previous note by Wikipedia. Maybe, you should look at the peaks near those frequencies