I had the privilege to sit on a sofa next to a real virtuoso 
playing the hurdy-gurdy.  (Disclaimer: I like bagpipes too, but this
sounded much nicer).  This was at a house party after a concertina
workshop in Western Massachusetts.  Everyone here calls my monkey organ
a hurdy-gurdy, but I knew what the real thing was but had never seen
one in the flesh before, let alone heard one.

It was a joy to hear him perform French folk tunes.  Besides
manipulating the keys (which are out of sight and of variable spacing),
the player does a lot with the crank.  By varying the speed, he can
control the volume and make the drone strings sound louder for rhythmic
emphasis.  Some drone strings are called "trumpets" and are set up to
respond only above a certain wheel speed, so a good cranking hand gets
you a rhythm section!

Some or all of the drones can be switched off, for variety or playing
in a different key.  The melody keys are pretty much fully chromatic.

Doesn't the Hupfield Phonoliszt control volume by varying the wheel
speed?  Yes, I recall seeing one perform that way.  And maybe the Mills
Violana modulates its speed also?

Mike Knudsen