Digital signal processing is usually a task for PCs with customised software or at least 32-bit microcontrollers - however with some clever coding an external circuitry an Arduino or compatible can also perform some functions, and one of these is beat detection.
This process is explained by Damian Peckett who not only explains various methods of DSP methods but also the Goertzel Algorithm used in his project. With the addition of a small preamplifier circuit the Arduino can receive an amplified signal from an electret microphone and determine the lower-frequency sounds.
For more information about the process, including example circuits and sketches - visit Damian's interesting website. And for more, we're on facebook, Google+, and twitter - so follow us for news and product updates as well.