FFT & the Spectrum: The Acoustic Prism
The waveform is what sound "looks like"; the spectrum is what sound "is made of". FFT is the algorithm that turns a waveform into a spectrum.
White light passes through a prism and becomes a rainbow — each color is a different component of the white light. Similarly, FFT "takes apart" a complex waveform and tells us "how strong each harmonic is". The result, drawn out, is the spectrum: x-axis = frequency, y-axis = energy (dB). The waveform and the spectrum are two views of the same sound.
Experiment 5 · Open the Prism
Above is the waveform (like white light: all components stacked together); below is its spectrum (like the rainbow the prism splits out). Click "Open prism" to watch the transformation animation: white light → decomposition → rainbow spectral lines, each line being one frequency component — the higher the line, the stronger the energy. The sliders below are exactly the same as Chapter 4 — there you stacked harmonics to see the waveform; here you take the other view and split the waveform into its lines.
Waveform = how you look at time; spectrum = what exists in frequency. The next 6 parameters are all "read" from the spectrum.