Buss loading, clipping, distortion, etc: a discussion

[wheever]

Hi kids!

So, I think there is some conventional wisdom regarding clipping and distortion on busses and channels when mixing in DP that says something like "you can't end up with audible clipping or distortion on anything but the output buss, and thereby the converters, because DP runs 32-bit float internally and that's more headroom than God has" or something. Am I correct in my understanding of this trope? Because, if I am, the trope is wrong and I've been doing it all wrong for years.

Let me explain: I've got this huge (85+ track) mix I've been working on on and off over the last year or so. The mix is structured so that 10 sub auxes are feeding a main aux which either feeds the outputs, or feeds a stereo track (that is then monitored) to record mixdowns.

Operating under the assumption that anything that doesn't hit the red too hard was okay, I've been letting the sub busses load up on the high-RMS sections with impunity. But I was hearing a "thickness" or "grainyness" in those sections that I assumed was a function of the various warming plugs on everything, or was perhaps hitting the outputs and the converters too hard.

Finally, the other day, I had everything sounding like I wanted it to, but there was still too much of that murk in those loud sections. First I rejiggered the automation so that the MAIN output buss never made it closer to -10. But it was still there. Then I bypassed all the processing on that MAIN aux. But it was still there. Then I started turning off all the warming/character plugs and, other than the changes one would expect, the murk was still there. Let's be clear: nothing on the mixing board was hotter than about -16. From looking at the mixing board the levels looked low.

So I did me a little looky-loo at the meter bridge to see if something was overloading that I hadn't noticed, and lo and behold Buss 1-2 (which the subs feed, and which feeds the MAIN aux) was spending all of its time on the loud passages IN THE RED.

So I thought about it for a bit, and decided the best way to approach it was to drop the levels on the sub auxes via changing the automation. Once I did this, buss 1-2 stopped clipping and everything cleared up and sounded like it should. Then just for the info, I undid the automation changes and instead put a MASTER on Buss 1-2 and pulled the sucker down until the loud passages were no longer clipping, and that worked too.


So now the mix sounds F-ing awesome and exactly like it should. But it brings me (long-windedly) to "I thought you couldn't clip DP internally?" What the heck?

And the lesson for me is look at the meter bridge! Stuff is going on there that doesn't show up in the mixer levels!

Thoughts? Discussion? Flames?

[Shooshie]

I've found it to be easier to clip the busses than I previously believed. One place that I keep watch is in the Audio Monitor window. Its meters, I think, more accurately reflect what is going on internally.

Shooshie

[donreynolds]

I've found it to be easier to clip the busses than I previously believed. One place that I keep watch is in the Audio Monitor window. Its meters, I think, more accurately reflect what is going on internally.

Shooshie

I do too. I have my audio monitor open all the time and periodically check my meter bridge. I try not to clip any. I hear the clipping usually and have to find it and take care of it. I guess clipping is alright for tape but not in DP .

[wheever]

It is also my experience and I agree: the meter bridge more accurately reflects the state of hotness of the buss. But agreement isn't really a discussion.

[cbergm7210]

In my experience I have resolved to not worry about the occasional red clip light on buses, but that it can be a noticeable sonic problem when going too far, IE distortion. Stating the obvious, I know...

I agree with the OP that in my mind I would like to know how much room I actually have before I need to worry about this. (How would this be measured?) I have read and archived Magic Dave's comments about the improbability of clipping DP internally.

[Umbrella]

Correct me if I'm wrong, but I seem to remember from somewhere that DP's Master Fader(s) are 64-bit wide...

Even if they are, I'm not sure if this would make any difference...

[slotz71]

I would agree with the "thick and grainy" sound when loading busses too much....
I finally got my mix setup tweaked a year or two ago and I don't clip ANYTHING anymore, channels, busses, aux's and especially not outputs. My mixes have never sounded better. "Jump out of the speakers", "Wide and open" are some of the phrases that I hear to describe my mixes... and they are LOUD... well, as loud as what's out there commercially and not distorted... I do use a lot of outboard compression and analog summing and I know that doesn't hurt. I might let a snare track clip it's own channel once or twice in a song but other than that I don't every see red clip lights in my mixes.
Maybe it is true that only the output busses clipping is what you really need to worry about since the mix engine is crunching along at 32 bits, but I figure if you can do it without clipping anything, that can't be a bad thing....

[heyitsjimi]

I dunno you guys, I have a 26 track (so far) mix. I didn't hear any nastiness, but I was red lighting a couple busses. Perc stuff. After painstakingly pulling down the offending hits, I didn't hear any difference at all. The output busses weren't clipping, & the audio monitor only clipped once over the 4 minute song. Maybe if you're only seeing clips rarely, it doesn't matter in anything but the output busses..... or maybe it's cumulative, as your track count goes up, the nastiness does, too ..... or maybe perc hits are so short they sneak through. Anyway, I really couldn't hear any difference, even soloing, A/B ing, etc.

[wheever]

I dunno you guys, I have a 26 track (so far) mix. I didn't hear any nastiness, but I was red lighting a couple busses. Perc stuff.

Yeah, it's fine on percussion. I was more talking about situations where the RMS keeps the meters loaded into the orange or red, not necessarily hitting the clip. Re-gain staging changed everything for me in the mix. Suddenly things were much clearer and crisper. I try to keep the levels at like -12 now.

[magicd]

Why guess? Test it for yourself.

I put a commercial drum loop in a stereo audio track. The loop is mastered so that is as loud as possible without clipping.

I added a trim plug-in and provided 40db of boost. That means the output of the track is 40db over unity gain.
Output of the audio track goes to an aux track. On the aux track I have a Trim plug-in that removes 40db of gain from the signal.

Output of the aux track goes to a second audio track.

Record.

Phase invert the second audio track. Sum the original with the new. You get a flat line. The audio that has been boosted and then cut by 40 db within DP cancels perfectly with the original audio.

Dave