“Ob-xd is based on the Oberheim OB-X. It attempts to recreate its sound and behavior, but as the original was very limited in some important ways a number of things were added or altered to the original design. If you’re unfamiliar with the OB-X, its user manual can easily be found from various sources on the net.
The Ob-xd was designed to sound as good and as rich as the original. It implements micro random detuning which is a big part of that sound. However, it was not designed as a self-contained completely independent soft-synth. It needs to be contained within a VST framework where things like transposition, automation, layering, arpeggiation, etc., are available. Also, like many synths of the OB-X’s generation, the Obxd has no internal effects so its sounds and textures can be greatly enhanced by the use of additional processing like chorus, reverb, delay, etc.”
Source : obxd.wordpress.com