In the meantime you might want to notate some ideas: http://scorecleaner.com/ (uses also C++) or do yourself a bit of algorithmic composing (http://www.symboliccomposer.com/page_main.shtml,. since the 90's). And together we wait impatiently for http://opusmodus.com/ to be available (down for maintenance right now).

I'm trying to figure out why you posted this, it just seems like a non sequitur. Setting aside, for a moment, the issue of performance on signal processing tasks, from a GUI perspective there's no reason that an interface akin to Ableton Live shouldn't be producible in Common Lisp, Clojure or any currently maintained Scheme implementation.

If you're dependent on 3rd party C/C++ libraries for the signal processing, many schemes are pretty good for FFI, I've not used Clojure FFI or Common Lisp FFI so I can't comment much on them. Clojure seems like it would be as good or at least no worse than Java for interfacing with existing C/C++ libraries. Common Lisp FFI is going to be implementation dependent (like with scheme). I do know that Chicken Scheme's FFI is pretty easy. I made a wrapper for a subset of GLUT and OpenGL, and adding additional components as they became relevant to the project was straightforward.

Regarding performance, I won't comment on Common Lisp or Clojure, I never measured their performance for numeric tasks. Scheme, however, with something like Chicken Scheme has good performance, and again FFI is straightforward so making a C module to do some heavy lifting is not unreasonable.