There's not much you can make wrong when using Natural Volume. The two (or actually three) things to keep in mind are:

1. Natural Volume makes only sense when it gets used for all instruments of an arrangement.

2. Due to the huge dynamic range covered by the different instruments of an orchestra, most instruments bar a very few have to be set to surprisingly low volumes, to allow for the necessary headroom of the few loud ones. If your arrengement  seems to be too quiet then, either raise the volume*) of all instruments by the same amount, or simply bring up your master bus' volume to meaningful levels.

3. Natural Volume is meant to be used as a starting point. Don't expect this feature to be the answer to all your mixing tasks.

*) "Raising the volume" is not the same as "using a louder dynamic layer"!

BTW - this is what MIRx' Manual tells us about Natural Volume on p.11:

HTH,

Thanks for these explanations about natural volume.  Dietz, another question for you, is there any particular ideal input level for MirPro?  -18?  

I can fully understand why many of the instrument's natural volume level is on the low side because there needs to be headroom for a few loud instruments in the range of the natural volume slider.

This brings up a whole interesting discussion about how hot to run Orch VST instruments, with MirPro, because of the above issue, the levels are actually quite low, by necessity as you explained, but we have two opposite goals, one goal would be to bring each instrument into the DAW mixer right around -18, or perhaps at zero using K-20 metering, etc.  But on the other hand we have a goal of having orch templates where the overall orchestra is level-balanced, and the natural volume fader is a very nice hint from VSL about where that should be, rather then bringing all the instruments into the mix at -18 and then subsequently adjusting the DAW fader's to achieve the desired balancing..which I could also call "pop" mixing too FWIW.

I am generally adding a gain plugin on the master bus to bring the overall level back up to what I want, which is not hard, presuming I don't try to mix any other non-mir instrument, etc. it just brings all the levels up again, unless I use a loud instrument of course, then I'd have to bring that gain back down, and you have suggested other work arounds.

One suggestion for MIR3D, if would be nice if there was a global control built into Mir3D that acts like a VCA within Mir...to bring the level up, without having to apply a post-gain to it.  It would essentially "reduce the amount of gain reduction" in an adjustable away so that all instruments sitting on one stage would have this same change...and rather then reducing all the levels and then bringing it back up again, it would simply change how much they get reduced to begin with, if that makes sense.  That way with smaller ensembles and such they would not need to be reduced nearly as much and could be adjusted globally for the entire MIR stage.

I didn't know about the ALT option..but on Mac no ALT key....  I tried OPTION, CMD and CTRL, none of them behaved that way.  Would be nice to know...I would use that feature..since there is no global control. (EDIT, looks like on Mac you have to select all the channels you want to change together as a group after setting that in the preferences, then be careful in the future to remember not to move any sliders while multiple channels are selected unless you go back and uncheck it in the prefs.  This is a bit awkward, but it works)

Can I ask you a deeper engineering question...  if you have inst1 set around 0db and inst2 set at say -30db...and then we link them and move the slider...the audible difference per db is different for each of these two  instruments. because of logarithmic scaling..  I'm assuming that any kind of linked control like that would lose the exact relative relationship.  Or does it?

Well anyway I guess its easier to just use a gain plugin once for the the whole mix.  Especially since I might have stuff in seperate VePro instances using seperate MirPro stages, etc.

Thanks for that video Dietz!  The reason it didn't work for me before was because I was trying to option-slide the actual natural-volume slider in the right window pane...and that doesn't work apparently.  It does work that I can option-drag the icons to edit them all as a group...and/or....can option-drag the the volume slider on the left pane channel list...which is the same as it appears to be attached to the natural-volume slider over on the right side inspector...

I will fool around with that some more...might be useful.  My new template is dividing my template up into a dozen or so VePro instances...so in some ways its easier to just put a gain plugin on a master bus in my DAW.. Otherwise then I have to worry about getting the balance between VePro instances to get out out of wack with each other.

The main concern here is about having a level-balanced orch that is somewhat realistic so that as I'm writing and orchestrating I will not be hearing unrealistic blending, and thus result in poor orchestrations.  By using Natural Volume, hopefully its fairly close to reality and I can orchestrate in a somewhat realistic manner.  Once the music is written, then the job of mixing can uncheck anything I want and move faders around any way I want until it sounds the way I want.  IMHO.

In any case as you said, with 32bit its probably not that much of a concern going down and then back up again in level.  At least in this case where I am doing rather minimal FX processing to each orchestra instrument...there might be a tad bit of EQ or something like that, occasionally a limiter on timpani or something, but generally I am not processing those individually...so there really isn't need for the signal to be normalized IMHO like might be the case for some analog modeled plugins or something.  What is more interesting is establishing the right level balancing so that I orchestrate realistically to begin with...which is what the natural volume checkbox hopefully provides.  It just usually needs to be a bit louder at that stage..until I bring in Timpani then I pboably have to turn it all back down again hehehe.