A programmable sound generator, or PSG, is a sound chip that generates sound waves by synthesizing multiple basic waveforms, and often some kind of noise generator, (all controlled by writing data to dedicated registers in the sound chip, hence the name) and combining and mixing these waveforms into a complex waveform, then shaping the amplitude (its "envelope") of the resulting waveform using "attack" "decay" "sustain" and "release" time periods, so that the resulting waveform then mimics a certain kind of sound.