A combination of FFT on input from an electret microphone and WebSockets for real-time applications.
###FFT
The FFT library I used is a simple one provided by the user dief on the arduino forums. I borrowed from a modified example by Paul Bishop and his Realtime Audio Spectrum Analyzer project. The frequency breakdown is from around 0-30 kHz with 0-500 Hz ommitted due to garbage values.
###Websockets
The WebSocket library comes from github user leg0 and was modified to send out a char array containing the 63 values per sample. The real-time data is then processed server-side to display an audio spectrum. There appears to be a 126 long char limit or the connection will time out, it's possible that adding a delay will fix the problem but I have not tried.