Pulse Width Modulation
A technique for simulating analog signals by varying the width of digital pulses, fundamental to chiptune synthesis for creating warm, resonant tones.
PWM works by repeatedly switching a signal on and off, but instead of a fixed duty cycle, the pulse width itself oscillates. A narrower pulse sounds bright and thin; a wide pulse sounds dull and warm; and constant, rapid modulation of that width creates harmonic content that static waveforms cannot. The Commodore 64's SID chip had native PWM support, making it a cornerstone of early demo music. Modulating PWM quickly enough produces complex, evolving tones from a single oscillator, which was why SID composers found it so expressive.