Portal is a granular effects engine, not playable instrument. It takes an audio input and stores it in a cyclical buffer, which is then sliced into small pieces of audio called grains. The grains are processed, and then stitched back together at the output of the granulator. Each grain can be changed using the SIZE, DENSITY, PITCH, PAN, and SHAPE controls. The currently stored audio buffer can be slowed down using the STRETCH controls, as well as delayed and fed back into the input of the granulator using the GRAIN DELAY.