This is just an example of what a musical scale looks like in Time Domain and in Frequency Domain. The notes here have been played separately (staccato).
Time Domain - Each peak corresponds to a played note -> Easy to separate them and get individual notes - The amplitude of the peaks represents the intensity (volume) -> It is not useful for the note identification Frequency Domain - Each peak corresponds to a frequency component -> Each component is the sum of the power for all the notes in the scale - It is not filtered -> We will implement a Butter-worth Filter later on. - It is not possible to identify the notes from this plot either. What can we do? Combine these two plots in ONE! -> Spectrogram