I have done some reed voicing for pipe organs.  It basically boils
down to --

- being sure the tongue and shallot surfaces are absolutely clean and
true; use ultra-fine sandpaper to buff these to a mirror finish;

- curving the reed tongue with a rounded burnisher so that it has an
exponential curve from the end to the tip, increasing at the tip end;
increasing the curve makes the tone smoother with more fundamental
depth, but also slows the speech; flattening the curve makes the speech
faster but the tone thinner and more brash; excessive or insufficient
curve will simply silence the pipe;

- adjusting the resonator length so that the vibrating pitch of the
tongue fully couples; as specified in Dom Bedos' treatise (l'Art du
Facteur d'Orgues), test the pipe by tuning the tongue sharp until it
flies off to a very different, higher pitch, then slowly flatten the
pitch just to the point where the pitch returns to normal; the optimal
resonator length is that which allows the pipe to sound in tune with
the tongue adjusted just below that "flip point," at which the pipe's
timbre as the ideal balance of fundamental depth and harmonic
brilliance.

The more reed voicing I've done, the more I've become convinced that
the variables are actually fewer than with flue pipes, and once one
understands the variables and how they interact, with experience reed
voicing becomes a pretty straightforward process.

Timothy Tikker