Several times in this thread people have mentioned log amplifiers for audio signals.
See thatcorp.com THAT2252
http://thatcorp.com/datashts/2252data.pdf
The output is +0.3 to –0.3 volts over a 100db range. A simple op-amp will amplify the 0.6 volt signal and add an offset to get 0 to 5 volts.