The checkbox to the left of Play sound enables or disables DCP-o-matic's use of sound. On some machines there will be multiple options in the drop-down menu to decide how the sound should be played.

The mapping matrix below specifies how audio from DCP channels will be routed to your sound hardware. By default, DCP-o-matic will mix 5.1 audio down to stereo if your chosen output device only has 2 channels.