Surely a calliope is annoying enough on its own?

Pip, I have sent some MIDI's to Joe. The first is an example of parallel fifths. It's very short.

Then there's the melody of 'To Canaan's Land I'm on my Way." It shows how we do it here in the Midwest. The hymn sites have a very religious version which is no doubt quite authentic, but it's a little too pious, I guess, because I never heard of it before today.

Then there's a MIDI of the descant that I learned from some old book. The song is in G, and the descant features a number of long D's. )D is the fifth note of the G scale.) There are also a couple of long B's. They permit a person to play either C or Em on their measures. Clever

Then there's a MIDI for the two parts together. The descant is only sung on the chorus.

There seem to be two principles (not rules) for bluegrass descants. One is that you start out on the fifth of the scale, and the other is that you use different note lengths from the melody (i.e. you change the lyrics a little) to make it more interesting. This can be done on the fly if the guitars are loud enough.