At the risk of asking a question that may seem daft to experienced players (especially as I haven't actually got my instrument yet)...
I see on Neil Brook's trompette workshop that his method for the coup de 3 and coup de 4 assumes you complete the coup over a single revolution of the crank (so I'm guessing 1 turn = 1 bar of music). Given that the tempo of different tunes can vary considerably, am I right in thinking that the chien responds to variations in the speed at which you turn the crank, rather than the absolute speed? Otherwise you'd end up with a constant buzz during tunes above a certain tempo.
Again, sorry if I'm showing my lack of experience - I've yet to meet a hurdy gurdy player in the flesh, so the internet is my only source of information!