Hi list and Trond,
I'm using the tl.crossover4~ (thanks, Trond, it saved me from having to kludge my own crossover filter).
Some other tl filters (like butter*) have a "quality" option to make smooth sweeps. crossover4 doesn't appear to have it. Is there some other command I can use? I might need to switch the frequency during a performance. If I do an an abrupt switch, there's a momentary loud distortion. If I use a line object, the distortion is quieter but lasts longer.