Ratios and bells
Whole ratios sound like instruments; odd ones ring like metal.
Lesson 2 of 4
The new partials FM adds sit at the carrier’s frequency plus and minus multiples of the modulator’s. So the ratio between the two decides which partials you get.
Bell tones
Try B Coarse 1 to 8, then move B Fine.
Each operator modulates the one below it; the ones on the output line are heard. Click an operator to see its own waveform and spectrum.
With whole-number ratios (B Coarse 1, 2, 3…) the partials line up with the note’s harmonics, and the sound has a clear pitch, like a string or a reed. Watch the spectrum: evenly spaced peaks.
Now turn B Fine up. The ratio is no longer a whole number, the partials fall between the harmonics, and the sound turns into a bell, a gong or clanging metal. The waveform stops repeating cleanly, and the spectrum’s peaks are no longer evenly spaced.