The letter DF are for Double Filter this version have two filter that can be separated left and right, all oscillator and FAT option are splited left and right, this give this little synth a very wide stereo sound. Softplug added to it the best Adventus 1.5 options like the X-Knob and filter velocity respond. According to Softplug the Adventus DF is NOT an update but a seperate soft synth.