Harmonics

Additive synthesis involves manually controlling harmonics, and uses only sine waves.

Building upon research by Roger Shepard and Jean-Claude Risset, Deutsch found a way to build a "staircase" of musical tones that seems to both go up without end, and just like in Escher's illusion, they appear to never go up to another octave. By changing the harmonics of each tone, Deutsch had in effect, turned a linear musical scale into a circle.