The “mda” plug-ins are legacy, open-source plug-ins developed by Paul Kellett and colleagues. See About the MDA plug-ins and http://mda.smartelectronix.com/.
The mda Ambience effect simulates “room ambience”–not quite reverberation, but an enhanced stereo sound similar to hearing a sound source within a room with hard walls.
Like all the mda plug-ins, mda Ambience does not have its own custom GUI, so Unify presents it using a “generic” GUI consisting of a stack of horizontal sliders, one for each of the plug-in's parameters. Note each of these parameters is also available for automation.
Size: size of the simulated room, 0 to 10 meters, default 7 m.
HF Damp: amount of filtering (“damping”) of higher frequencies, percentage 0-100%, default 70%.
Mix: dry/wet mix, percentage 0 (all dry) to 100% (all wet), default 90%.
Output: output level, -20 dB to +20 dB, default 0 dB.