The D-550 is the rackmount equivalent of the Roland D-50, Roland's first fully digital synthesizer. Its synthesis is touted as Linear Arithmetic, which consists of layering periodic waveforms with sampled attack transients. Editing on the D-550 is not as convenient as on the D-50, due to the lack of vector joystick, soft buttons, and data entry slider, although the void is easily filled with the PG-1000 programmer.