(I copied and edited this post from where it was buried in another thread)
So, we all love how many Kontakt orchestral libraries use the mod wheel to smoothly crossfade through the various dynamic layers of samples, instead of using note velocity to do this. Although it's not immediately obvious, it's very easy to do this in EXS-24.
The key is in the easily-overlooked "Xfade" parameter box in the upper left of the EXS front panel, and the first (left-most) mod routing in the matrix just below.
The Xfade parameters controls how the transitions from one velocity zone to another are handled. Even if you program all of your velocity ranges to NOT overlap (which is what I do), entering any value above zero for Xfade Amount will create overlaps. The numbers in this field correspond to the range of 0-127 of note velocities, or MIDI CC that can be substituted via the mod matrix. Here's how they work:
Let's say you have a very simple sample map - just one soft sample (assigned to Vel Range 0-63) and one loud sample (assigned to Vel Range 64-127). If you enter a value of +/- 64 for Xfade Amount, then the
overlap range will be +32 and -32, centered around the split point you set up in the Editor - meaning that for velocities between 0-32, only the soft sample will sound. Starting at velocity 33, the loud sample will start to fade in, until at velocity 64 both the soft and loud samples are played at equal volumes. From velocity 65 through 96, the soft sample will fade out, and from 97 through 127 only the loud sample will play. So the Xfade Amount value determines the width of the velocity range over which the overlap / crossfade will occur. The Type parameter just controls the shape of the crossfade - db Linear, Linear, or Equal Power. Your ears will tell you which to use.
So, that's part A of the equation - creating velocity crossfades. Part B of the equation is performing this crossfade from an incoming MIDI CC instead of note velocity. This part is super-simple, but not immediately obvious. Basically, that left-most (first) slot in the mod matrix usually defaults to Src (Source) = Velocity, Via = n/a, Dest (Destination) = S. Select - indicating that incoming note velocity will "select" the sample. If you change the Src from Velocity to Ctrl #1 - boom. Instead of changing between Velocity Ranges of samples that you've set up inside the EXS Editor, now Ctrl #1 (mod wheel) will perform that function. Of course, any of the choices in the pop-up menu under Src can be used - any MIDI CC#, LFOs, etc.
Note that note velocity may still be affecting the Amp Volume (via the split Level slider in the upper right of the front panel), both ADSR Attack times (via their split sliders), as well as other parameters via the mod matrix.
The great thing about this is that you can set up all your EXS Instrument sample mapping (inside the Editor) as though you were only going to use Note Velocity to select dynamic layers, and then decide on a per-use basis to substitute Ctrl #1 (or whatever) for Velocity in the mod matrix, and fine-tune the Xfade amount and curve type to suit the situation as you go. If you reduce the amount of that slider in mod matrix slot #1 to less than maximum, you'll never hear the loudest layers (whether you're using Velocity or Mod Wheel), so this is a great way to force EXS to "never get to" the loudest dynamic layers.