With the help of an Arduino and a variety of RGB LED strips, you can add colourful reactive lighting to any device, including a piano as described by Instructables member DangerousTim. This process involves a simple electret microphone and amplifier circuit to boost the ambient noise for measurement by the Arduino's analogue input.
Then the Arduino sketch can determine which LEDs to activate depending on the strength of signal from the amplifier circuit. With this example the loudness of the sound will be the point of difference as opposed to the frequency, however this could also be experimented with using different code.
To experiment with audio sampling yourself you can make an easy start with a simple electret microphone board, and our Freetronics MIC: microphone and sound module is perfect.
The MIC: contains an integrated dual signal amplifier converts the sound to separate channels for pulse / frequency measurement, and sound volume (pressure) level. Designed to connect straight to an Arduino compatible microcontroller, Analog to Digital converter, or many other circuits. For more information and to order click here.