Pulse width modulation

modulation of the symmetry of a square waveform. this generates a lot more higher harmonics spectra / overtones.

nice for fatten or thicken up sounds like pads / strings and fat basses, especially introduced on smaller synthesizers to get a bigger sound our of one oscillator.

short: PWM

the Pulse Width (PW) is fixed while PWM is the modulation of the symmetry.