It's a compressor. The settings depend totally on the track. It's a confusing compressor in my opinion, but for it to make a little more sense, click on the "attack/release" tab. I think it sorta' acts like 2 compressors, with the bottom set of numbers (level detector) compressing the signal on the way "in,' and the top set of numbers compressing the already compressed signal. This can be useful if you're used to working with analog gear where stuff is compressed on the way in and on the way out (this is little more than a guess to me...I've read about that being done, so that's all I'm basing it on).
Anyway...from a practical standpoint, don't mess with the level detector settings unless you know what you're doing, lol. I make changes to the attack and release settings in the top box. VERY generally here, lower signals (bass, kick drums) will have longer attacks and slower releases. I mean, I feel bad even saying THAT because there are about 400 exceptions. The best way to get an idea is to take different types of tracks and play around with the presets and listen to how each sound is effected when the attack/release/ and ratio settings are changed. Then play around with your own settings for all the parameters. I have some VERY VERY long attack and release settings for the low end stuff...for example, for stuff below 80Hz, attacks of 200ms and releases up to 2000ms with enormously ridiculous ratios, like 10:1 above -18db For stuff between 100-500Hz, maybe attack of 75ms and releases of 1000ms. Again, these numbers are meaningless, but in general, lower stuff uses longer attacks and releases, and vice versa as you go up the scale.
As a primer on compression, you can use it on idividual tracks and/or on the final mix...sometimes multiple times on both. Compression is a huge subject, but that's all the dynamics processor is.
