Some good info here: (http://www.digido.com/honor-roll.html) and here: (http://www.digido.com/level-practices-part-2-includes-the-k-system.html) There's a plethora of variables, when one is considering recording levels. BASICS: we have the noise floor. This is the lowest level, where tape hiss and electrical hum reside. Next we have the nominal level, which is the level that is best for recording your incoming signal, in order to minimize distortion and overcome the noise floor. The distance between the noise floor and the nominal level is called the signal-to-noise ratio. Next is the maximum level, which is where distortion occurs, when your incoming level reaches it. This is the highest level in the total dynamic range. Distortion is something that you definitely want to avoid unless you are versed in the skills of good tape saturation (sometimes engineers will try to slightly distort the signal by pushing it over the maximum level because this will give a stronger sound to an originally weak one). However, in digital recording, any distortion due to overpeaking is distasteful.). Now the difference between the nominal level and the maximum level is referred to as your headroom. This is your safety zone, and this is needed to account for some stray peaks here and there without hitting the maximum level. And to wrap this up...the whole thing, from noise floor to the maximum level is called the dynamic range. Then there are compressors, (which I've always eschewed) that enable one to cram more dynamic range onto the recording(albeit, somewhat distorted). I've always tried to stay around -3db to '0' on my VU meters(which also vary, with regards to sensitivity(of course), when averaging, on music with moderate dynamic range. Then -6db with wider dynamic range stuff.