http://www.synthtopia.com/content/2013/06/17/free-open-source-music-synthesizer-android/
The Synthesizer app got mentioned here a week ago and it is confirmed now that it will be expanded upon and as mentioned before it is open source and implements code for the lowest possible latency on Android- So guess it would be interesting as a developer to go and take a look at the code...
The developer says:
There’s experimental USB MIDI for devices that support it, and lots more code that’s in the source repository but not hooked up end-to-end, including a high quality sawtooth generator and the start of a sequencer.
Music Synthesizer for Android