how to avoid clipping on post fader bus sends?

[jacko]

[this is a theoretical debate about Pro Tools HD headroom and the lack of it on post fader sends]

how to avoid clipping on post fader bus sends?

let's imagine I have an audio track with a peak level 0dBFS

I push its fader to +8dBFS, then, to avoid clipping, I bring master fader down to -10dBFS so I don't clip the master. My output level is -2dBFS.

Up to this point everything is fine, because master fader shifted the dynamic range of my mixer. I gave myself 10dB of headroom.

In the next step I activate post fader sends on my audio track - for fx and parallel compression. Then I am screwed, because the send on the track is already clipped by 8dB due to the channel fader pushed by 8dB up. Is there any option in Pro Tools HD to address this situation? Something that would shift the dynamic range of my bus send on each track and that would give me some headroom.

[Stig Eliassen]

With all due respect, you're screwed long before you create that send.

Basically, you have to re-think the way you record and mix. If the audio has a peak level @ 0 dbFS, and you have to push that up 8 db, you must know that this can't be good? To avoid clipping - don't record so hot. Simple as that.

[ericsvizeny]

You want your peak to be at -6 dBFS when recording. This gives you headroom for post processing.

Eric

Sent from my Droid using Tapatalk

[jacko]

You missed my point. This is just an example, not the rule of my mixing. I will not lower all my signals to -12dBFS just to let myself use full range of my faders.

The situation I described does not pose problems on floating point digital mixers (Pro Tools native) nor analogue consoles.

I KNOW that I could mix in the way the post fader signal never exeeds 0dBFS. The point is - master faders in Pro Tools allow you to do so, which makes mixing easier, because you can keep all your faders in comfortable range of -10 to +10dBFS, rather than -20 to 0.

Master Faders shift dynamic range of output busses. It would be great to have the ability to attenuate post fader sends too. Currently there is no headroom for them.

[fakir_cz]

Exactly. What you are doing is similar to running an analog console @ +20 dB! No headroom at all. It seems that you have misunderstood the whole digital levels and gain staging principle (otherwise you wouldn't say funny things like "+8 dBFS"). This way you are not only in constant risk of clipping a mix bus (any of them), but also most of your plug-ins are way off the optimal level range.

A quick fix to your problem is to put a Trim plug-in in the first slot of all your audio tracks, set it to -20 dB. This will make mixing much easier. But your audio shouldn't get anywhere near the 0 dBFS, that's way too hot and you should avoid it in the first place.

edit: ah, I've just read your response. While you can use master faders as you say, you're still complicate things for yourself. Your gain staging is wrong and your use of master faders is in fact just a workaround to make it work. The fact that you don't have problem on a floating point system does not mean that your way is right, it's just the nature of the system that it can stand it. But it's definitely not true with analog console - as I said, 0 dBFS in digital world is somewhere about +24 dB VU (depending on calibration) in analog world! I have yet to see an analog console that would be happy if you constantly feed it with such levels. That's why you have this problem - the system is not designed to run so hot, that's why there is no way to attenuate post fader send, because noone ever thought that someone can run it that way. You are trying to cure a symptom, but you are missing the cause. I don't see why you would need to use such insane levels just to keep your faders in comfortable range - get your tracks to about -20 dBFS (use Trim plug-in to make their levels approximately equal), set your faders to unity gain and start mixing from there - if you keep the average mix level around the -20 dBFS, you have about 20 dB of headroom, which is plenty. If it seems quiet in this stage, just turn up your speakers. Once you get your mix done, you can then do the mastering stuff and get your mix to usual CD levels.

[midnightrambler]

Originally Posted by milaszewski

You missed my point. This is just an example, not the rule of my mixing. I will not lower all my signals to -12dBFS just to let myself use full range of my faders.

This doesn't make any sense. You can still use your faders between -10 and +10 with signals printed at -20dBFS. Your overall mix would just be quieter, which frankly would be a good thing.

0dBFS is the LIMIT, not a TARGET.

[midnightrambler]

Also, you could do what I (and no doubt others here) do and set a basic balance and then use the faders in Trim mode to fine-tune that balance: so in essence you're always balancing the yellow faders around the unity mark, and the original level of the fader becomes almost immaterial. (That old SSL training eh)

[jacko]

I will quote something from Pro Tools 48 Bit Mixer document:

In the Pro Tools 48-bit mixer however, this is not the case. By shifting the original 24-bit word to roughly the middle of a 56-bit register, there is enough headroom to sum 128 full-code tracks at +12 without internally clipping

That is of course an extreme example, but shows that Pro Tools give you headroom that you don't get even from an analogue console.

The problem is that, as far as I am currently aware, there is no way of using post fader sends in this extreme example and that, in my opinion, defeats the purpose of having this huge headroom.

I am very sorry that all of you concentrated on me doing something wrong rather than trying to understand what I am asking about. I am not stupid and I am a relatively successful mixing engineer with rich knowledge about sound engineering in general.

[jacko]

Originally Posted by midnightrambler

Also, you could do what I (and no doubt others here) do and set a basic balance and then use the faders in Trim mode to fine-tune that balance: so in essence you're always balancing the yellow faders around the unity mark, and the original level of the fader becomes almost immaterial. (That old SSL training eh)

Thanks, that is a good suggestion. And I think I might go this way. Currently I work the other way around - I use volume trim as my automation layer. This way I can always see all my automation rides on faders and still be able to offset the overall level just by moving the fader. On the other hand, sometimes it would be better to have static faders with the automation moves "hidden".

[fakir_cz]

Originally Posted by milaszewski

I am very sorry that all of you concentrated on me doing something wrong rather than trying to understand what I am asking about. I am not stupid and I am a relatively successful mixing engineer with rich knowledge about sound engineering in general.

Jacek,
it is not our intention (or at least mine) to make you look stupid or anything like that. Perhaps we've just haven't got your point. I try to understand it again so please correct me, if I'm wrong: It really seems that you have headroom problems because your tracks are recorded too hot. And they are so because it enables you to have faders in "comfortable" range (so let's say somewhere about unity), right? If so, it is not necessary since it definitely is possible to mix with tons of headroom and faders in "comfortable" range at the same time.

So, that's why I don't understand your problem - it seems to me that you are making a basic mistake and then wondering, why it doesn't work. And when we pointed out that the levels you've stated, even if they were just an example, are way too hot, you said that it wasn't what you were asking for. So that's why I'm confused.