A VU meter is an interesting tool which you may have seen on older Hi-Fi components as the display of LEDs or a moving meter to the music was always an interesting feature - however their purpose was to display the "loudness" or signal level of an audio input.
You can make your own version quite easily with an Arduino and some external circuitry, thanks to the team at the ArduinoHacks website. They demonstrate how to build a simple preamp circuit with the classic LM386, and convert the signal into one suitable for measurement with an Arduino's ADC pin. The matching sketch then translates the levels into a display with the use of six LEDs - or you could use another form of output to your liking. A demonstration of this is shown in the following video:
If you're interested in experimenting with sound and your Arduino or other development board, 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.