This application relates to digital PWM modulation. A PWM modulator (400, 1100) has a PWM generator (402) configured to receive pulse width data (PWidth) and to output a PWM signal (SPWM) comprising a plurality of repeating PWM cycle periods, in which the duration of any pulse of the PWM signal in each PWM cycle period is based on the pulse width data. The PWM generator is configured to synchronise the PWM cycle periods, and the start and end of any PWM pulse, to a received first clock signal. The PWM generator is operable to generate pulses that have a positional error from a centred position within the PWM cycle period and a pulse position controller (403) is configured to control the position of a pulse in a PWM cycle period so as to at least partly compensate for the positional error of one or more preceding pulses.