Fourier and signals.

Time runs left to right and one wave at a time wears the accent. A sine traced from a circle, Fourier epicycles drawing a treble clef, a square wave built from harmonics, an FFT spectrum and a scrolling spectrogram.

Sine from a circleA turning radius whose height traces one cycle of a sine wave.
Fourier epicyclesA chain of rotating circles whose pen draws a treble clef.
Square wave from harmonicsOdd harmonics adding up toward a square wave, ringing at the jumps.
FFT spectrumA compound wave above, its frequency magnitudes as bars below.
SpectrogramA time-frequency heat map with a rising chirp cutting across it.