The Pro/DGX is a thirty preset monophonic analog synth based on the Pro-Soloist of the 1970's. The main difference is that the Pro/DGX had electronic switching (touch buttons) between its preset sounds whereas the older Pro-Soloist had circuit-based switching (rocker switches). It has 30 preset sounds to choose from, including Flute, Bassoon, Brass, Fuzz Guitar etc. Other features included pitch, portamento, vibrato, growl and wow effects. The keyboard has 37 keys with aftertouch sensitivity for volume, brilliance, vibrato, wow, growl, and even bend effects (all at once if you desire!). A few basic filter, envelope and LFO controls allow some tweaking of the preset sounds, however there is no memory to store your settings.
The Pro/DGX sounds slightly different than the Pro-Soloist however. The presets are virtually the same, but the Pro/DGX implemented a new filter design which some say sounds worse than the one used in the Pro-Soloist. Both synths refer to their single filter control (the filter cutoff) as "Brilliance". A few additional control sliders are available for the Volume, Portamento Time and Aftertouch Amount. Later on during its production, the Pro/DGX was released with the "Orange+Black" look of later ARP synths. It has been used by Tangerine Dream and Keane.
Demos & Media
Images from Perfect Circuit Audio and Audio Playground Synthesizer Museum.
Thanks to Lee Matthews for providing info.