The speed that you turn the crank controls the tempo. Also,you have to turn the crank smoothly to keep the tempo even. After you play a roll a few times you have a feel for when to change the stops. Of course, there are really no rules, so I do it a little different each time.
Thanks! There are three groups. Musical Box society, Automatic Musical Instrument Collectors association, Carousel Organ Assoc. of America. You can find them all on the interwebs.
With a little practice it's no problem. Plus, as I mentioned in another comment, you can do many changes or none at all, it really sounds fine either way.
actually you have to know the score to know when to do that, right?I like that it's being much more engaged, like the pianola you have to watch the tempo