That's close but it's not what the progression is, the last chord isn't just an A-B-C-D, it's F-G-A-B-C-D. They're diatonic chords, not chromatic - the latter would indicate they were not scale related, which they are
It goes: 1:A-B-C.......... 2:B-C-D.......... 3:A-B-C-D.......... 4:F-G-A-B-C-D..........
there's 4 chords not 3. Also there's an E in the bass so you could think of the chords as being from A minor scale. They're all closed voicings which gives the it a distinctive soft tone, that and of course that they sound very sine-like in quality.
You can try a patch made on a synth with a self oscillating filter too, you get almost sine like sounds which can be tracked to keyboard so you can play chromatically. Also, if you've ever used electric piano and taken off all the overtones until you are left with an alomst sine wave sound, you get similar tones that way too but to me, they're just sine waves either way