Console Channel levels vs stereo bus levels?

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Redsandblu

Member
Joined
Apr 7, 2005
Messages
17
Location
Brussels, Belgium
Hi All,

I was wondering on your approaches on stereo bus output levels (while mixing) in order to keep those levels under control: here's the situation:

we send all tracks (separately) from PT HD to an SSL console. The stereo mix is converted to digital with a HEDD192 and recorded in Sadie.
PT is referenced to 0VU = -18dB(FS). Most of the time, the tracks we get (to mix) arrive at fairly hot levels (distortion guitarsliving in the -2 to -4 dB range). So, already by sending out everything at 0 out to the SSL, the console's meters tend to be pegged from the start.
Throw in a few dB's of compression where needed and we'll end up with a mix that is WAY too hot (By the way, on the SSL's output 0 VU = -14dB). Not to mention that it is also too hot for the HEDD (also calibrated for 0VU = -14dB).
So what's to do?
1/ Lower the master fader on the console? possibly yes, but if the levels are that hot, will the tracks not already be distorted prior to their arrival at the quad bus? or at the quad bus input?

2/ Lower the output levels in PT so that the tracks hit the console at a lower starting level? Is that a good way to start or would you rather recalibrate PT so that for instance 0VU=-14dB (and thus reducing the headroom by 4 dB??)

3/ Bring down the individual faders by x dB? Yes but this is not an option when you're halfway a mix as it changes levels to sends, submaster inserts etc...

4/ Recalibrate the HEDD? 0VU=-16dB is the most you can get (I believe) but then that would still not solve the problem if the quad bus is overloading??


How do you folks deal with this? How's the headroom and calibration thing affecting you?

Thanks & All The Best,

R.
 
Well, 0VU = +4dBm, so if you have the HEDD calibrated for 0dBFS at +18dBm, that means that your actual 0VU is indeed -14dBFS and nor -18dBFS, as you say your pro-tools is.

I always contend that there really is no absolute way to refer VU meters to FS digital metering, since so much depends on dynamic content and the crest factor of the waveform (distorted rock guitars are totally different from pianos in several very important ways) but it is generally held that over 0VU you should have at least 14dB of wiggle room... so if you only have 14 and then choose to mix lower...

Your question as asked doesn't really have a simple answer. In the days when 16-bit audio was as good as it got, the idea was usually to record as close to clipping as possible without actually clipping. For instruments with a high crest factor, this produced low VU levels, and vice-versa. The rule was simple. Ignore VU meters. Consider them to be utterly useless for digital conversion level indication.

Now, you don't say what SSL you're using. I'm going to assume that it's an E or G series. These are blessed with a VCA TRIM adjustment that turns your mix down by reducing all the VCA faders. Understand that FX returns should be set to "i" (isolate) on the thumbwheel switches, so that they don't get turned down as well.

3/ Bring down the individual faders by x dB? Yes but this is not an option when you're halfway a mix as it changes levels to sends, submaster inserts etc...
I'm not sure I get it... you should want post-fade sends to go down, or the instruments will get wetter, unless I'm not understanding your point?

Basically, if you have a "broom handle" mix (as so many pro-tools users semm to do, where all the faders are set at equal level and the console is almost just an expensive summing amp with some FX sends and returns and some analogue EQ) then you can just use a broom handle to pull the faders back a bit. Leave the FX returns alone, or the signals will get drier (signal goes down by 1dB, send goes down by 1dB, return goes down by 1dB... -result, signal =1dB lower, effect =2dB lower!)

The VCA TRIM and "i" (isolate) allows you to trim the faders globally (but even works if the faders aren't "straight-lined", since it's a master VCA reference voltage) without affecting the FX returns. It also prevents the FX returns from soloing if you use a VCA group solo. You should always use isolate for FX returns, for this reason alone... it makes life so much more wonderful!

The only result is that the mix buss level is turned down without affecting the balance. Wonderful if you're clipping the mix buss. However, the signal level drops where the compressor senses its threshold, so you might have to trim that up a little as the VCA TRIM is turned down. The trim works up as well as down, with a ±15dB range, and an in/out button. It works as well for driving the mix buss harder as it does for backing it off.

However...

If you have good levels into the HEDD, close to zero without clipping, then this might all be a complete waste of time. If you're just worrying that the VU meters are pegging, that's just because there's a lot of RMS energy in the signal. If the console isn't overloading and the HEDD isn't overloading, all that will happen is that you'll get the mix back onto therange of the VU meters, then the HEDD will not be at the top of it's range. (There is some debate about whether it's so important nowadays, -Nika Aldrich seems to suggest that you shouldn't even PEAK above -18dBFS, and while he knows a LOT more than I do about it, I cannot go along with that. I agree that 24-bit has so much resolution (even if it's only scarcely over 20 bits in actual realization) that you don't have to sweat it if you aren't playing "tease or dare" with the clip indicator, but if your music doesn't have surprise crescendos or suchlike, it simply doesn't make sense to me to throw 3 bits away... I'm more cautious with live stuff, specially if it's classical in nature, but mixing a PT session is much less risky, so I say push it.

submaster inserts etc...
Using submasters, isolate the faders going TO the submasters, then leave the submaster faders (post-insert) to follow the VCA trim; same result.

How do you folks deal with this? How's the headroom and calibration thing affecting you?
Don't pay too much attention to VU meters. then there's no calibration worry. If the clip point of your electronics matches the clip point of your converters, pay atention to your converter meters and watch for overload lights elsewhere in a varying gain-structure (like heavy EQ cuts or boosts) and you're golden. VU (RMS) level won't really tell you what you need to know to avoid clipping; Peak metering will.

Keith
 
Do you ever hear board hiss?

Considering your levels and material, I really doubt it.

So nothing needs to be run "hot". No meters should be bent. This is an insult to your musicians.

The output level from your tape deck or DAC is a non-issue. The channel strips have gain controls. Use them! Individual channels probably don't have to be run even to 0VU; -10VU should be ample. And it may sound much sweeter when not flogged.

I'm not sure why you'd be tracking distortion guitars at -2dBfs. 24-bit has >100dB dynamic range; guitar doesn't usually have 60dB dynamic range. (If you don't make these tracks, have to take the files the client gives you, maybe you should either rationalize the levels in digital, or trim your DAC and/or board trimmers for digital full scale no higher than +10dBu.)

If you are doing Sinatra, you can mix at unity gain. When you have a star soloist, the sum of all other tracks will not rise much above the soloist.

If you are doing thick guitar fights, you must mix with a loss. Four maxed-out guitars mixed equally sum to 6dB higher than a single guitar. Four percussive tracks can mix 12dB higher, though 9dB might be a more likely sum. Since your master channel runs the same rails as your track channels, it has the same overload. So you either run channels 6dB-12dB low, or take 6dB-12B of loss in the summing amp (essentially the masters and submaster faders).

> not an option when you're halfway a mix as it changes levels to sends, submaster inserts etc...

Yeah, well, it helps to know where you are going before you start. And to mix, not "more of this" "more of that", but by pulling back the tracks that are stomping on the star's solo. There is no point in banging the analog needles: whatever comes out can be gain-adjusted on the digital side after the console. Capturing console out at 24 bit, for final 16-bit product, being 10dB or 20dB "weak" is not a real problem. And you ARE going to do a final level-normalize in the digital domain before you cut the CD.
 
in my humble experiences, with identical setups, I've learned that there is absolutely no reason to record gtrs, or anything else, that hot into any digital medium, PT or not. You' ll run into saturation hell no matter how many zillion$ costing convertors you throw at it.

Make the same recordings with your gtrs at +/- -20/-14 and you will get way more interesting sounds. Other way is to reduce the trims as PRR suggested, what brings down your dynamic range (I assume you recorded so hot because of dynamic range?)

Bottom line, do yourself and your clients a big favor and keep more headroom :thumb:

just a part of my 2 ? cents here.

Tony
 
my understanding is you are using the SSL as analog summing. If that is the case who says all faders have to be at 0. If you do that then your stereo buss will be too hot . Try this sometime split a 1 K signal @ +4/0VU into several channels and then bring each one up so that the fader is @ 0 on the silk screening. Watch what the stereo buss does. With only 2-3 faders up it will go over 0VU and into the red.
LIke as said b4 pull faders down and 2 watch were you put the monitor pot for control room monitors. If it is too low chances are you will raises the faders too much to compinsate so it is a good volume level in the control room. OR vise versa where the control room monitor is up too much their for your channels are not to loud. Bob kats has a good artical about this on his website.
here is a link.
http://digido.com/portal/pmodule_id=11/pmdmode=fullscreen/pageadder_page_id=93/
 

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