I had a couple of albums of mp3s that were encoded with really low gain. Rather than re-encode the mp3s (which wouldn’t have taken too long), I had a look for tools that would let me normalise these tools. I didn’t have a lot of luck, and then yesterday I saw a link to mp3gain pop up in my aggregator.
Mp3gain works by analysing the mp3s passed to it, then tweaking the mp3 metadata to adjust the gain. It doesn’t re-encode the mp3s. It can normalise the gain on a single mp3, or work out the ‘normalised’ gain on an entire album (or repository) and tweak each mp3 to bring it in line with the others. To be honest, I didn’t even know mp3s had metadata you could tweak to do this, so it didn’t occur to me this was an option.
I ran it across the albums in question, and it decided they were consistent within themselves. Rather than run it across the entire repository, I increased the gain by a set 3dB, and then after listening to the resulting output, another 3dB. Maybe one day I’ll back up my mp3s and run it across the entire repository. This works pretty well for now.