Converting VCSL sample libraries, I encountered opcodes `xfin_lovel`, `xfin_hivel`, `xfout_lovel`, `xfout_hivel` which allow to crossfade different velocity ranges (playing sample A for velocity V1, sample B for velocity V2 and mixtures of A and B with lesser volumes, for intermediate velocities V1 < V < V2.
What happens is better specified in the legacy sfz manual, in the big table of opcodes. One caveat is that by default the mixing of samples is by constant RMS power, not just linear scaling (but there is a setting to make it linear, see `xf_velcurve` there). It’s not elaborated much further right there, but I guess you just take the gain for a sample as a square roots of what crossfade ramps evaluate to (so the sum of squares of gains will be constant if one sample is faded in and other faded out in the same interval of velocities).
Is it possible to make this using the current DS version (reading so far, I don’t see how yet) and/or do you wish to implement that someday?