an Entity references as follows:
A constant timbre at a constant pitch is characterized by a spectrum.Along a piece of music, the spectrum measured within a narrow time window varies with the melody and the possible effects of instruments.Therefore, it may seem paradoxical that a constant spectrum can be perceived as a melody rather than a stamp. The paradox is that the ear is not an abstract spectrograph: it "calculates" the Fourier transform of the audio signal in a narrow time window, but the slower variations are seen as temporal evolution and not as pitch.