Harmonics & Timbre
A sine wave is pure but boring. A violin, a voice, and a saw wave playing the same note sound wildly different, same frequency, same loudness. That difference is timbre, and it has a beautifully simple explanation.
Almost every musical sound is secretly a stack of sine waves: one at the note's frequency (the fundamental) plus quieter ones at whole-number multiples, 2×, 3×, 4× and so on. These are the harmonics. The recipe, which harmonics are present and how loud, is what your ear reads as tone color.
This rack gives you the fundamental (slider 1, at 110 Hz) plus seven harmonics. Power on and build your own timbre. Watch the spectrum: each slider is literally one bar.
Try this: start from “Pure tone”, then raise sliders one at a time and listen to the tone gain edge and brightness. Then hit “Square-like”, only odd harmonics (1, 3, 5, 7), and notice the hollow, clarinet-ish quality. Odd-only recipes always sound hollow.
Checkpoint
Play both sounds. Which one contains only odd harmonics?