An Elementary Explanation
http://www.shure.com/support/technotes/app-meter.html
one chip replacement for the standard analog meters based on LM3915.
http://www.aaroncake.net/circuits/vumeter.htm
http://www.web-ee.com/Electronic-Projects/projects/disco_vu/index.shtml
http://www.geocities.com/SiliconValley/Vista/7055/oct98.htm
http://www.4qdtec.com/avu.html
logarithmic scale with 3 dB steps, based in LM3915 IC
http://sound.westhost.com/project60.htm
http://www.vintage-radio.com/projects/output-indicator.shtml
5 led VU meter
http://www.spelektroniikka.fi/kuvat/vumittar.pdf