Anyway, I've got the "windchime" chime patch pretty well nailed this week, and aspects of the drone working as well. The bigger gongs are yet to do. The drone will need a flanger, but I think that will be doable. I'm told flangers are not much more complicated than an echo with a very short delay time (that varies), and I managed an echo on the Theremin project.
If you can use GPL with CPE code, there's a chorus in Gervill you could extract (it has a flanger mode - a flanger basically being a chorus with attitude and tattoos
). I'm just in the process of forking this out myself for JAudioLibs - basically need to change the parameter calculations to be something sensible as opposed to MIDI values.
If that license is no good for you (or you just want the fun of coding it yourself), then it's basically a delay where the delay time is controlled by an LFO. You'll need a delay where the delay time changes on a per sample basis - once per processing block would probably sound odd. They're also usually done with a delay on either stereo channel with the LFO's out of phase with each other to give that "thicker" sound.
Sorry if that's going over what you'd already been told.
Best wishes, Neil