Sound pressure to db analog
First, you could rectify and zero-reference your audio signal with an external circuit BEFORE feeding the DC signal voltage "envelope" into your Arduino. That would double your effective measurement range because you aren't throwing away half the dynamic range accommodating the 2.5V offset.

10 bits will give you around 60dB of dynamic range if you use the full scale. Converting the linear voltage measurement to logarithmic (for deciBels) is a simple mathematical function.