[MASSIVE Master]

The "True meaning" of headroom is the space between the nominal (or "normal") operating level and the point of failure.

With digital, it's simple -- "Fine, fine, fine, fine, fine, CLIP!"

With analog, it's a completely different story -- "Fine, a little questionable, spectrally skewed, wholly distorted, CLIP!"

You'll notice that converters are calibrated to a point of line level... Let's say that a particular unit is at -18dBFS (=0dBVU). A signal riding around -18dB(FS)RMS is going to be at the "normal" operating level in that case. Depending on what you're recording, you might have peaks as high as -8 or -6dBFS here and there, but the "meat" of the signal will be riding around -18dBFS.

That's your "built in" digital headroom --

The analog side gets more complicated with "actual" headroom and "USABLE" headroom -- With a lot of gear, those are two completely different things. I have some gear that sounds fine when you're "overdriving" it 12dB hotter than it was designed to work. I have some gear that starts to sound like complete crap above nominal also - but technically, the circuit hasn't failed completely yet - So on paper, it's still considered "headroom."

The REALLY important part is to make sure you're TRACKING with a good amount of headroom. Personally? I rarely, RARELY if ever peak above -12dBFS at any time on any track if my converters are calibrated to -18dBFS. Usually lower. I'd rather have a clean signal peaking at -24dBFS than a compromised signal at -10dBFS.

Once you're "in the box" those analog rules go out the window (assuming you're STAYING in the box) as with your digital signal, as long as you're not approaching the clip point (-0dBFS) you're in reasonable shape.

Sure, there are exceptions -- You can "overdrive" a digital signal into a digital compressor and then turn it down at a buss or something. But I hope that cleared it up a little...