For automatical audio level adjustment, audio compressor, which has nothing to do with codec, is the solution. It will lower ,hence compress,the level of loud parts, has no effect on soft parts, thus reduce the difference between loud and soft parts, then add some gain to all the parts, now soft parts will become louder, and compressed loud parts will kind of return to origional level.
I do audio editing on another platform, so don’t know the exact audio filter in FCP. Normally you will insert the audio filter compressor at the audio output bus, since it will compress all the audio tracks, or you have to insert a audio compressor per audio track. The parameter settings depend on the actural audio parts, can’t give exact settings here.
BTW, it would be better to add another audio filter called limiter behind compressor, for the sake of audio clipping if you add too much gain in compressor.
Too Many Standards = No Standard = Chaos
FCP7, Mac OSX 10.7.4, BMD Multibridge Extreme
Pro Tools HD 1 v 8.1cs1