Re Busses in Gain Staging

It's not necessary for the sub-busses to hit 0 on the VU. You can pick any target you like as a reference, as long as it's not too far left of the center position (because VU meters get harder to read the further left of 0 you go). 
 
In fact, it's probably better to NOT hit 0 on a submix. When those busses get added together on the master, the level will likely increase, requiring your limiter to bring it all back down. 
 

 
The meters are adjustable to -14db or -18db and this should be taken into consideration.  I've learned from discussions here to pick the reference according to need, then use meters at each stage and adjust each stage so the needles just touch 0 on the peaks.  Stick to your reference throughout and there won't be any problem when you reach the end.  This seems to be more or less was is being done here.
 
I'm not sure that using the Satson Channel and Buss emulators gives you enough meters to see each stage.  And I don't see how the signal could be low when it hits your buss if it's near zero in the track that feeds into it.  Especially if there's more than one track near zero feeding into your buss.  It should be too high, if anything.  Does the Satson Buss reduce level on its own ?
 
Meters like those from Klanghelm are easy to insert anywhere you want to see what's going on.

Jeff Evans
Also when Paul P says get the VU meters to touch 0 dB VU on the peaks what he is really saying is loudest part of the rms component is hitting 0 dB VU. Real short term peaks don't actually move the VU much at all.

 
You're right Jeff, I should have been clearer in my choice of words since peak has a precise meaning.  They only 'look' like peaks on the meter,in reality I guess they're more like mountains.  So the summits of the 'rms' component.
 

I have got the Satson and yes it is good console emulator.  Although I have Mixbus now and for me that sounds quite different and better.  But it does mean complete export of stems and into another DAW.  For certain genres it is well worth it though as many here also agree. (All the VU's in Mixbus are calibrated to -14 which also happens to be my main ref level here for most work)
 
The VU should be OK in the Satson and it will certainly allow you to see rms levels pretty well.  It only has two references though so it is limited in the ref levels it can work at.  (It is nice to just switch into -20.  All I have to do is recalibrate my real VU's and drop everything incoming that is down 6 dB)  Also the ballistics of the meter may not be quite as real in the Satson as say the Klanghelm ballistics are.  I read a bit more into meter ballistics.  I have found virtual VU's move in many different ways compared to the real (quality) VU's. They are hard to beat as they move in such a beautiful manner.  The Klanghelm meter is surprisingly close!
 
I don't use the meter to add or subtract gain.  (That could be confusing. Some how gain magically appears in your staging) If all your track levels are at the rms reference level than it is always easy to get any buss to reach 0 dB VU as well. The balance of track faders feeding a buss determines this final buss level. If I find a buss is low in level eg say it is reaching consistently around -4 dB VU then I grab all the tracks feeding that buss as a group and increase their (track faders) level slightly and it usually does the trick.  I use the Presonus Faderport and it is excellent for fine tuning stuff like this.  If a buss level is reading -1 or -2, I tend to leave it.  Being fractionally low won't hurt.  This is level before the buss fader.  I fine tune buss faders as a group that are feeding the stereo buss.  They often end up close to unity or -1 to -2 dB as well.
 
I find I can get all my tracks sitting at say -14 dB VU (rms level), all my buses which contain various mixes of track groups at the ref level and the final stereo mix at ref level.  With care and fine balancing I find it is possible.  And at the same time all the mixes on the buses and the final stereo buss are perfect.
 
Ballistics comes into play.  A buss may appear as being over loud but it could be some wild VU needle swinging instead.  (eg one or more tracks has poor dynamic control hence making levels erratic)  A compressor set right will tame that wild swinging  (buss or at track level usually on one offender) and the needle starts to move much better.  It pumps up nicely to 0 dB VU but does not go over.  You only need mild compression and the ballistics settle right down and now the level has gone from wildly moving up to + 3 dB VU to a more fluid action easing up real nice and just hitting 0 db VU.  Dynamic control on buses is great because it can tame a whole bunch of tracks at once.  Removing un needed frequencies also helps to tame wild swinging needles.  The VU meter has a response to DC actually so it can show very low un heard frequencies.  And also very high frequencies that don't need to be there.
 
Think about when the mix on say a buss is right, the VU is now going to show you that lovely mix in the form of a smooth but dancy ballistic.  When a mix is wrong the needle does not move well at all.  I can tell that something is up.  You can almost mix using a VU.  After a while you learn how much to push each track fader up.  First one to about -4 db VU etc... As the other stuff comes into a mix at the right balance and level the VU just ends up hitting 0 dB VU and it is moving great.  On a stereo buss if your vocals are tool loud the VU will move a bit wrong and the level will be too high.  Once you settle vocal levels right down to the right spot then the VU is now showing you the music and the vocals together and it just starts looking about right.

It actually makes no difference in terms of fidelity whether you turn up the tracks going into the bus or increase volume at the bus itself. Either way, you're doing the same thing: multiplying the data by a constant multiplier. Do whichever method you are most comfortable with.
 
You could, however, make a mathematical case that it's not preferable to reduce track volumes and then make them up at the bus. That may be where Jeff was coming from.
 
Keep in mind that we're talking about levels going into the master bus, not the final post-limiter levels. If your levels going in are conservative, then you leave more options about how loud the final master will be. That can change depending on your final destination (broadcast, MP3, YouTube, DVD/CD) and you probably don't want separate mixes for each.

Love Blue Cat's gain plugins! Especially for volume-matching vocal clips.

When a VU meter is swinging wildly it can mean the ballistics of the meter are telling you have not tamed the dynamics perhaps. Once you start controlling dynamics nicely the VU does not swing anywhere near as wildly. It changes quite a lot even with mild compression.
 
What VU meters are you using as a matter of interest. I must admit though that the real thing and real nice expensive ones at that still move in a nicer way and in a more fluid manner. I think when it comes to ballistics the actual real meter is probably very hard to beat. (I suspect it may be harder to emulate than what people think)
 
I am spoiled in that regard because I use the hardware meters most of the time and I know it is not something many are able to do.
 
The Klanghem meters are pretty good though and close. But they can still tell you what is going on. When the meter is moving nice and just hitting 0 dB VU then you know the rms level is at the reference level. So they can be accurate. The problem with other types of VU meter and even ones that show you accurate rms readings they fall down in the ballistics department and don't let on as much as the real ones do re dynamics being a little out of control.
 
Read the VU response of a real nice mixed and mastered CD. See the difference. You will have a different opinion about them then. (preferably not a smashed master either, one that has some nice dynamics in it) Adjust them so they are just hitting 0 dB VU most of the time and observe. Steely Dan's 'Everything Must Go' looks great on a (good) VU. A great example.

 
The Klanghelm meters have to be adjusted to the reference you choose.  If you choose -20db, and set you meters accordingly [not with the gain knob in the middle, but the (red) "VU" value at the bottom right of the meter, click and drag up/down], when the needles just touch zero the level is really at -20db.  So the zero on the meter is your reference.
 

Jeff Evans
When a VU meter is swinging wildly it can mean the ballistics of the meter are telling you have not tamed the dynamics perhaps. Once you start controlling dynamics nicely the VU does not swing anywhere near as wildly. It changes quite a lot even with mild compression.
 
What VU meters are you using as a matter of interest. 
 
Read the VU response of a real nice mixed and mastered CD. See the difference.

Hi Jeff,
 
I understand what you mean by the dynamics may need compressing --- but as I put the VU meter as the first plugin in the chain, its coming before any compression.  Isn't this how it should be done?
 
I'm using the Klanghelm software meters at -18.
I can understand how a final CD mix will have a more smooth response, but surely that is to be expected compared to individual tracks which will have relatively more dynamics?
 
I'm still trying to figure out how best they can work for me.  I've had good examples where I can see the VU meters going +4 in the red eg on a bass track - here I can easily lower the output on the soft synth to get it around 0VU and then raise the fader at output to get the right balance in the mix.  But, on the othe rhad, I'm having a problem with for example sustained string patches which only get the VU flickering at -10/-7 even when the output is maxed, even though the volume output seems good.   Similarly, fast sequences eg repeated 16th note patterns sometimes also show -10ish, even when the output volume is good and peaks even -2dbfs.    If I raise the output there to 0VU I'm going over 0dbfs with peaks ...  I guess that could be because of the fast transients, but that does not explain the sting patches showing very low in the VU.   
 
 

Thanks again Jeff ... I had just started to experiment with adding gain on those string patches - now what you said makes perfect sense there.
 
When you say "VU's are great but you also need your peak metering and you use both at the same time" :  I also just downloaded the demo of PSP Triple Meter, which shows VU, RMS, and Peak meter all in one.   I found that the RMS meter there, also calibrated -18, is much easier to see - those fast sting spiccatos are showing 0 here, when the VU meter is still -3/-5 down.   On other patches the VU and RMS meters are more or less same.   I'm not actually sure the difference - I thought the VU meters were measuring the RMS .. anyways, that PSP RMS needle just seems to be more easy to read, less fluctuation so easy to set for 0.  
 
I'm going to use both for a while, I guess most important is not to let it get over 0VU too much, use gain where necessary, and for fast transient patches rely more on keeping the dbfs peaks in check at not past -6.   I'm trusting that will get me most of the way there, safely ... :-)

I think it is important to get the balance right on each buss and yes not move track levels going into buses after you get that mix right.  My buss level faders are often still at 0 dB or unity but the rms level on a buss is often below my ref level.  eg  If I am working at -14 all the way through a project, then buss levels will be 3 to 4 dB down on that but then the buses usually all sum back to a balanced mix sitting around -14 again which is what you want.  The buses in my projects have slightly higher headroom than the tracks themselves.  They are often carrying a more complex signal so they might benefit from some slight extra headroom.
 
Headroom is great. The sound quality is very consistent over a wide range of digital ref rms levels these days. So working down at -14 or -20 is a breeze.  The sound there is pristine and transient and dynamic.  I rarely see overs anywhere when everything is running nice.
 
The SPL level in your studio is an important level to set and get right.  That is where you get the volume and power from your system.  My system sounds devastating when I turn it up loud and I can go loud anytime and it is good to listen to a mix loud for a while.  It can be very revealing.  I also really like listening way down soft in mono on a small mono speaker.
 
Gain staging is important and I never get bored talking about it.  After a while every project you do ends up with levels being perfect everywhere.  Tracks, buses and the final master buss.  It is something that existed in the analog days and the whole concept can be lifted across into digital.  It sounds better there and there is no noise now.  Transients are better.  As a drummer I can hear it big time.
 
I find VU meters really help me achieve great gain staging every time.  Peak metering is important now.  Work with both at once.