# Confused on the difference between the frequency spectrum of an entire song, and the frequency spectrum of a point in time

I am very much a beginner in this field - but find it really interesting. However I am a little confused on a certain area of knowledge.

If I have understood correctly: At any point in an audiosignal, for instance when someone is strumming a D-Major on a guitar, i can reproduce that exact sound in that moment by looking at the frequency spectrum for that time, do a Fourier Transform, and recieve a periodic signal in the time domain presented as a fourier series. If I play that signal, I will hear the sound that was in that exact moment of a song, just as a never ending note. In this scenario the frequency spectrum tells me what pitches were played- and the frequency domain will change for point in time.

However, If a look at a three-minute-song in the time domain, I dont quite understand what the fourier-transform will tell me. If I have this audiofile, and I view it in the timedomain, what will it tell me? (view picture) And if I transform it to the freq. domain, what will it tell me?

As far as my logic goes, I wont ge able to tell any of musical features just of an amplitude value in the time domain.

(And the confusion continues when we sample an audiosignal, and all we get is an amplitude value for a given time. How can any musical information be there?)

• any moment in time doesn't have a frequency. It can't – how would you assign a frequency to a single audio sample in isolation. Nov 5, 2017 at 14:43