You can open an edit window for both the synth and effect. If they do not have a custom edit GUI, the generic editor view will be used.

It is primarily intended to be used by Audio Unit developers for testing purposes, although it can be plenty of fun to play with all by itself. It is conceivable that you could even use it for live performances. In the end, I would like SynthTest to perhaps become an open reference implementation of an AudioUnit host. I also plan on adding more developer-oriented features, like property and parameter inspection, control over input and output busses, and support for more of the music device features like groups and instruments.