Digital Sampler/Delay

From the manual:

The BOSS DSD-3 is an effect unit that features both the sampler function (800ms digital recorder) and the delay funciton (50 to 800ms).

The Trigger In Jack can be used to sync the DSD-3 with a rhythm machine, or to sample a sound and use it as an external sound source, or to obtain an echo effect that perfectly syncs to the rhythm.

https://archive.org/details/manuallib-id-2725053