[theinternetftw]

A great way to get a behind-the-scenes glimpse of these videos (and Bill's production process in general) has been to check in on his vimeo accounts ([1] and [2]).

It's not quite what you're looking for (a simulation of the machine, which would be amazing to see in its own right), but according to this video [3], it looks like they've built a neat webapp for the purpose of having a sort of fourier synthesis playground.

Unfortunately, there's just the demo video, with no link to the site itself, and searching turned up nothing. They may plan to release it later on in the series.

[1] http://vimeo.com/engineerguy/videos

[2] http://vimeo.com/user17826495/videos

[3] http://vimeo.com/101539582

[engineerguy]

I had forgot about the Sum Some Sines .... that will come out ... it is a program on the processing language that lets you play with adding sines. It isn't a simulation of the machine, but it is fascinating and instructive. We choose not to release it with the machine vids.

[theinternetftw]

A note if you're not aware of it (though you probably are): processing has an offshoot called processing.js [1].

That version can run most processing apps within the browser with no plugins or setup, thus letting interested users just visit a link to use the app.

[1] http://processingjs.org/