How about noise floor?
All equipment has a noise floor....
What I'm looking for is dynamic range above the noise floor.
Say my noise floor is at @-100+dB. That's the level that all the noise from the transistors and the power and RF interference etc. is at in this theoretical recording chain.
For Example:
Say I have a instrument that has dynamic range of 70dB. If I set it to peak at -1dB, then the quietest part is at -71dB, which is still 29dB above the noise floor. Noise not very noticible right now.
But.... If I am peaking at only -20dB then my instrument during the quietest passage would be mixed with all of the noise just to be audible.
In fact, the ratio of the noise in the entire mix would be up to 20dB higher if I wanted this instrument to be clear in the mix because I'd have to then amplify that recorded signal (including the noise) another 20-30dB. That brings my noise level up to -70dB to -80dB. Now you start to hear the noise....
I personally hate the sound of my converter's noise floor too. I can actually hear my hard drive scanning. Yuk.
Basically, when I record I'm trying to put as much distance between my quietest passages and that equipment noise as possible!