This is really cool. Nice going. I'm amazed to see how many people have been working on similar things. I took a shot at this a while ago (http://soundtype.com) but I was stuck using Java for MIDI. Really looking forward to the MIDI spec for the Web Audio API.

Being that this is HN many of you might have seen this already, but there's an exciting Google IO talk from Chris Wilson about Web Audio: http://www.youtube.com/watch?v=hFsCG7v9Y4c

And see the corresponding slide deck for code: http://webaudio-io2012.appspot.com/#1