How viable would it be to do realtime audio processing on a typical smartphone? Specifically, I need to be able to count syllables as they're being spoken into a microphone. Accuracy is not that important, but it needs to be realtime(or close), so sending an audio recording to an external service for processing wouldn't work.
Before you head down the road of trying to figure out FFT, I suggest you try using the MediaRecorder instead. It is far simpler than AudioRecord and you can use it to analyze amplitude differences. You can use the code mentioned here.
Also, there is a more complete implementation of the various code you need for a clapper inside of the gastlib github project.