Levelator

The Levelator is "software that runs on Windows, OS X (universal binary), or Linux (Ubuntu) that adjusts the audio levels within your podcast or other audio file for variations from one speaker to the next, for example. It's not a compressor, normalizer or limiter although it contains all three.  (It) corrects for medium-term variations in loudness instead of the short-term and long-term variatons processed by compressor/limiters and normalizers, respectively." Source

Download The Levelator here: http://www.conversationsnetwork.org/levelator