For the development of the embedded synthesizer of the Striso I developed a target for the audio programming language Faust to run it on the STM32F4 microcontroller.
The STM32F4 is a very fast microcontroller running at 168MHz, having very fast ADCs and an FPU, making it possible to efficiently run a synthesizer.
There is a very cheap demonstration/development board available from ST with an audio codec and accelerometer, which makes it a great choice for developing self contained instruments. This board is called STM32F4-Discovery, and is very cheap at about €16.
The source code for the Faust target with an accelerometer controlled synthesizer is published on GitHub at https://github.com/pierstitus/STM32F4-Synth. There is also an example of a simple synthesizer written in C in another branch.