I have a large music and video collection but the audio levels are all over the place. How can I normalise them so I don't have to constantly adjust the volume myself?
Signed, Sound Advice Needed
This is a tough situation because the solutions vary and none of them are all that great. It also depends on where you're listening to your music and watching your videos. If you want to handle this operation dynamically, you may have to implement several solutions.
The Long, Tedious, But Permanent Road
Because the only permanent solution is to actually change the levels and save out a new version of your audio and video, we'll take a look at that first. This process can involve re-compressing your already compressed audio, which means quality loss is inevitable, so unless you're working from high-quality sources you may want to avoid this option.
To do this, you need something that can process audio and boost the levels. Free software like Audacity can easily normalise your levels, but if normalisation isn't cutting it and you need to compress the dynamic range you'll need something that can apply a compressor or limiter. Audacity has a compressor and, chances are, you have other software that has somewhat more complex options as well. For example, if you're using a Mac, Garageband has effective compressing and limiting plug-ins. An alternative is using something like The Levelator, which employs several techniques to boost the signal of your audio. While it might not be ideal for music (as it's designed for podcasts, primarily), it's a good option for spoken word content.
These techniques are great for audio but can be a major pain for video. While you could use video editing software you might have lying around, either normalise or compress the audio, and then export the altered file, it's just a whole lot of trouble that's not really worth it if this is going to be a regular operation.
If you don't want to manually process every single one of your media files — and no one would blame you — you may have some hardware options. Believe it or not, televisions are often equipped with some nifty audio-altering tools like equalisers and compressors. If you haven't messed around with your TV's audio settings before, now might be a good time. Go in, explore, and you may just find what you need.
Alternatively you could go all out and purchase a hardware compressor, then run the audio signal through it, and into your TV's input. If you do buy a hardware compressor, be sure to check the latency so your newly-compressed audio isn't lagging behind. Most boxes can keep up (because they'd be otherwise useless) but that's not the case 100% of the time. Make sure you check before you buy.
There are a plenty of ways to do this on the software side. If you're running XBMC, you can use dynamic range compression to handle it on the fly. Note: we have not been able to actually locate this setting where it is supposed to be. It seems it's only in some builds of XBMC on some platforms. If you use iTunes, the Sound Check feature will adjust all the volume of your music and videos to a more equal level. If you're on a Mac but not using iTunes, Perian can adjust softer videos to play louder. If you want those effects system-wide on your Mac, Hear is a paid solution ($50 — ouch!) that will give you a spectacular amount of control over audio from all sources.
There's really no perfect solution, unfortunately. Dealing with audio volumes can be a bit of a problem. These are just a few ideas we've come up with, but if you have some suggestions, let us know in the comments!