Realistic string legato

Great questions... and complicated to answer because the capabilities of the real instruments are of course so much more varied than the VIs. Also because sample libraries use their own lingo and the meanings of "slur" and "legato" in VI land are only tenuously connected to their real life meanings.

So to simplify: a "slur" means connecting several notes on the same bow stroke. The notes can be on the same string or different strings. They can be notes that are played using the same left hand position, or the left hand can move during the slur. The details don't matter: the slur can be made very smooth, almost imperceptible, regardless of how "complicated" it is. A lot of practice goes into making sure those transitions are smooth and don't draw attention, and the natural amount of vibrato tends to mask any imprecision. On the other end of the spectrum, a player can exaggerate the transition. Hence instead of a very smooth left hand motion, they can make an exaggerated slow soupy-sounding motion: that's portamento. However, there are many shades here between black and white. Slur transitions are generally slower in slow, emotional music and become more fast, precise and transparent in fast playing. Just like vibrato is generally wider and slower in slow music and becomes tighter and less prominent in fast playing. Cinematic Studio Strings represents this better than any other library I've heard.

So that's slurring.. "Legato" playing by contrast is using different bow strokes for each note BUT smoothly connecting them so that the bow change is practically unhearable.

(and there are many many many other bowing techniques than these: staccato, tremolo, jete, martele, detache, col legno, spiccato - only a few of which make it into sample libraries).

But let's suppose we have a passage that's a smooth, singable melody. It will be played with a combination of "slurs and legatos" (this is a weird, "VI composer", articulation-based way to think of it: the musicians would just think of it as a legato passage where some notes are under slurs).

To decide where we're going to play legato, and which notes are slurred, starts to involve the question of bow speed. Bow speed and bow pressure are related and are used to create (the entire) dynamics of the instrument. You can think of the bow length as being slightly analogous to breath. You don't want to "run out of bow." And when you "use up" the bow fast, as a rule of thumb it's because you're playing loud, heavy, accented material. Bow direction is also important. The down bow (pulling the bow to the right, away from the instrument) is naturally a bit heavier and more accented than the up bow, although again a lot of practice goes into trying to balance these. So some very rough rules of thumb for bowing are that you would use slurs to join up notes that are subsidiary to others - passing notes in a phrase. Like if you had a measure in 4/4: C, D, E-F G where the E and F are eighth notes, you'd slur those two and perhaps keep the other 3 notes as three separate bows. This creates symmetry as you can see: the 1st and 3rd beats are down bows, and we're ready for another downbow on beat 1 of the next measure. It's hard to go wrong by just applying the two rules of "make things line up so strong beats get downbows" and "make things line up so that passages of the same duration get the same amount of bow." Here, we satisified both those principles by slurring the two eighth notes (which make up a quarter note duration, the same as the other notes we took on a single bow). Now if the passage was much FASTER, then we might divide the measure into two slurs: "CD" "EFG" (again notice the balance in duration). Or we might just have the strings play all the notes separately. That totally depends on the character of the music. A lot of times (with newbie composers) the players just decide for themselves on the scoring stage what the right interpretation is.

I have to go see a movie (with my music!!!!) but I'll type a bit more about how the left hand interacts with bowing when I get home. Hope this was useful!