"2sus" is not an acronym. It's just short for something like "to sustained".
I've always said that's the greatest feature of Vienna Imperial and the one thing that still sets it appart from the rest of VSL pianos. It gives it an amazing touch (and even more, a feel for the player) of realism.
What is it exactly? It emulates very effectively what happens in a real acoustic piano when you press the sustain pedal or release it AFTER you already pressed notes in the keyboard.
How does it do it? It loads two samples per note/velocity. One is the unsustained sound sample, and the other is the sustained sound sample. Then it switches between the dry sample and the sustained sample as you press or release the pedal, no matter if you are in the middle of a note/chord. That's what a real piano does. And that's why your polyphony gets reduced to half - because you need double the amount of samples at the same time for that to work.
In a real piano, if you play a chord without releasing it, and after a second you press the sustain pedal, you clearly hear a complete change in the sound, as you are opening the rest of the strings and they start creating sympathetic resonances.
In the same way, if you you first press your sustain pedal, and play a chord without releasing it, you'll immadiately hear that chord with a lot of sympathetic resonances, like a kind of reverb. But, if you haven't released the chord and after a second you release only the sustain pedal, you also hear an immediate change in the sound, going from big to dry as the sympathetic resonances are muted.
To me, that's a HUGE deal. I've told VSL in the past that I consider it a terrible mistake not to have included that feature in any of the Synchron pianos. When I play the Vienna Imperial for myself, without any reverb, I can enjoy the sound and feel really inspired, and what happens with 2sus enabled makes me feel very close to what I feel when playing an acoustic piano. But not with the Synchrons. Those have beautiful samples, and they may be good mixed with an orchestra or with lots of room reverberation (as in most of their demos) - but they don't feel natural for the player in their dryest setting, because you can't hear any reaction to the sustain pedal when you press a chord and then the pedal, or when you release the pedal with your hands still on the chord.
After all these years, Vienna Imperial is, to me, the greatest virtual piano ever created. It's still the only one I enjoy playing for inspiration. I also have several of the Synchron pianos, and some times those sit better into a mix when I produce pop music in my studio. But, for the experience of playing it alone and getting inspired, nothing beats the Vienna Imperial. To me.
Cheers,
Francisco
