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Old 12-20-2018, 10:47 AM   #16
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Originally Posted by karbomusic View Post
In the analog world, we obviously can exceed "zero" but in digital, zero is the impassable ceiling.
Somebody on another forum wrote something similar. I know that you know what you mean here, and so did he, but I just feel the wording in both cases might be confusing to some people, so I'm copying my reply from that thread. Much of it has been covered above already, but...
Originally Posted by ashcat_lt
Please don't confuse 0dBVU with 0dbFS.

In analog, the mark that says 0 is usually the nominal or normal expected operating level. It tells us nothing about the actual limits of the circuit. Most times there is 15-20db above that mark before you hit the rails and start actually clipping. Things often get curvy before that point. Sometimes we like how that sounds.

In digital, the 0 mark is the limit. That's exactly as loud as a fixed point digital file can get, and exactly as far as your converter (ADC or DAC) can get. The digital part is perfectly linear right up to that point and then just suddenly clips off. We usually don't like how that sounds. Sometimes the analog electronics get curvy before the digital part clips off, so sometimes it's not so bad.

This is exactly the reason we have that -18dbFS rule of thumb. Our converters are designed to top out at more or less the same level as the analog gear we attach to it. We said earlier thats usually +15 to +20dbVU, and very often +18dbVU. So the limit of our digital system (0dbFS) is set to the limit of our analog system (+18dbVU) and therefore the nominal analog level of 0dBVU hits digital at -18dbFS. But actually that's just a rule of thumb, and if you want to know how your converter works, you have to look at its specs and usually do some math. They never make it easy. I think my line inputs are calibrated to -20dbFS, but I've seen some with as little as 12db headroom above analog nominal.

Worth mentioning too that the analog VU meters are showing you an average very much like (close enough to) a short-term RMS or LUFS level. It's normal for actual peak levels (the ones that actually matter when we're worried about the limits) to be much higher, and on some sources if you have then right on 0dBVU will still end up distorting or clipping. This confuses a lot of newbs. The digital meters they're looking at are almost always peak levels, but they heard -18dbFS, so they shoot for that and end up quieter than they really need to be. That means nothing in digital really, but it means you're running the analog end of things much lower than it's nominal level and much closer to its noise floor. That's only a problem if it's a problem, but in a lot of cases it can be noticeable. It's complicated quite a bit by the fact that for most of us at home with all in one interfaces, we don't get VU meters. The only meters we have are those in our DAW, which are usually peak based.
But also yes, just turn the knobs til it sounds good. I don't have any preamps worth overdriving, so I just shoot for out of the noise floor but not clipping. In the mix, you just do what you need to do. The way to know if you're hitting a plugin too hard is to listen.

Edit - Actually in some situations where either I don't have a lot of time to dial things in or I don't really trust the source to maintain its level or I feel like I might need to match the recording some other time, I'll just turn my pres all the way down. It's the only place on the knob that I know I can find exactly every time. Well...the other end, too, but that's obviously not appropriate in most cases. Noise is better than clipping most of the time.

Last edited by ashcat_lt; 12-20-2018 at 11:00 AM.
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