FYI:
This topic is discussed at length in _The Design Patterns Smalltalk
Companion_ by Alpert, Brown, Woolf under the Observer and Command patterns.


   --- james mccartney     james at clyde.as.utexas.edu   james at lcsaudio.com
If you have a PowerMac check out SuperCollider, a real time synth program:
http://www.audiosynth.com