Thanks Pancenter. Great story about the SC-55 demo.
Not to go on too long about realism, but I found an online demo that's a good one to critique. Go to the following link and listen to demo number "4.2 String Orchestra Descen" of this Mirsolav Vitous string library:
http://www.bigfishaudio.com/detail.html?4;16;1:115::511988:::::G511988;A115::511 935
The purpose here is not to tear this demo to shreds. I rather like it and I think the sounds are really nice. My purpose is just to illustrate a few of the finer points to be aware of when doing orchestral realizations using samples.
As the demo progresses you'll hear a triplet figure in the violins. Listen closely and notice how the melody kind of ducks out of the picture during the second two notes of the triplet. The phrase sounds "mushy" because the attack of the samples (or perhaps the attack setting on the player) is too slow to articulate those notes clearly at the speed they're played.
After the pause you'll hear the triplet played a second time. The overall articulation of the notes is awkward there as well. In neither case do those phrases sound like they're played one one bow (legato). They don't sound like they're played detached either. It's somewhere in-between, and it's not an authentic sound.
How to fix it? One solution there would be to articulate that phrase with another instrument which provides an authentic legato sound. It could be from the same library or a different one. Whatever works. This part could be an overdub, leaving the MV sound in the background (which might lend some consistency to the overall sound). Or, the more authentic legato instrument could be used to replace the notes entirely in just that phrase. What works best is purely a matter of experimentation.
Next... listen for how some of the notes ring out in the last chord played before the pause. There's an Ab below middle C in particular that seems to end later than the other players in the ensemble. This makes the ensemble sound "loose", unconducted, as though the violas (?) weren't listening to the rest of the players.
How to fix it? One approach would be to go into the piano roll editor and edit the length of the notes so the result sounds like all players ended the phrase at the same time. That doesn't mean that you should make all notes the same length. A little "slop" on the end of a phrase is OK. But that viola (?) note's length should definitely have been made shorter. Easy fix.
Overall, the release time sounds a little too long. While a long release time helps to connect notes and play legato phrases, if it's set too long the overall sound starts to become mushy. Like reverb but without the characteristics of a room. I'd have shortened the release time a bit in the player, and then added some reverb to help connect the notes rather than depend on the longer release time to "glue" the section together.
So anyway, those are just some of the finer points that, to me, make the difference between, say, a sketch (in which it's fine to throw up sounds, compose, and tweak later) and a "final".