I got this for the low price and watched the video; in it, he says the input light should stay yellow and GR should be at around -3 for the plugin to be really working. For me, though, without pushing the input fader way up to 6 dbs, the GR barely moves and the light is only flickering yellow (the plug seems to be adding about 3 dbs to the overall level of the mix, though). I've been very careful about gain staging (I use Audio Vitamins' Structure plug on all tracks and the master, and I use both meterplug's Dynameter and Mastering the Mix's Levels plugins to mix dynamically and conservatively),  so I'm wondering if any of you know if I'm doing something wrong here? Might this be a calibration issue?

Well I am not a fan of Audio Vitamins Structure at all. Firstly it is you that should be setting your gain staging and rms ref levels not some plugin.  What this is doing is taking control over your levels and you have no real idea what the rms levels are that are flowing about in your system. 
 
From what I can see you have a rather low rms value hitting your stereo mix buss.  And hence you are getting not enough level going into CLA to begin with.  I am pretty sure CLA is set up for a -18 rms ref = 0 dB VU.  From what I can see Audio Vitamins is keeping things rather low on the tracks e.g. -22 as the rms ref or lower. 
 
I work at both -14 and -20 ref levels. -14 for me was pushing hard into CLA and I had to recalibrate it so a -14 test signal was showing 0 dB VU on the input meter. 
 
So switch your VU meter on CLA to IN and observe what the VU is up to.   With your mix it should be just hitting 0 dB VU.  What happens if you increase the input level control to get that.  The same with the OUT setting it also needs to be hitting 0 dB VU as well.  You can recalibrate CLA as well to suit your working rms ref levels.  But if you don't actually know what they are to begin with you may be in the dark a little and travelling blind.  It is a pity that you cannot tell Audio Vitamins Structure what ref rms level to calibrate to. 

I don't know about CLA mixdown. It's like an equivalent of a health supplement where you don't know the ingredients but in true holistic faith you feel better. First thing I noticed is that In and Out on the VU Gauge isn't really telling you anything other than it's being processed. I would only pay attention to the Input and Gain stages from the plug-in.
 
Officially the EBU and all of those people behind those mystic whitepapers are using -23dB as O dB VU or indeed 0 LU. I've been looking for a metering system other than the K-Metering. With the K-System I aim or K-12 unless the genre calls for less.
 
Anyway as you were.

Double Post

Jeff, thanks so much for the insight. I had no idea that Structure was calibrated so low- I had heard good things and just recently started using it to help me with gain. I guess whenever you try to find a shortcut you take a chance. I used to press my mix buss way too hard, so I've been trying to get used to mixing at lower levels and attaining a more dynamic sound versus the overcompressed stuff I've done in the past. My ears aren't what they used to be (probably in part because of my old mixing habits), so I try to use whatever tools I can to help, but it sounds like I may need to reconsider the Structure plugin- one danger sign is the very limited documentation provided for it. I will say it has helped me get better at gain staging, and it wasn't too expensive. Anyway, many thanks for this post and the many others I have read; your thoughts are truly helpful.
 
One last question if you don't mind: do you have any recommendations for test signals I could download?

interpolated
I don't know about CLA mixdown. It's like an equivalent of a health supplement where you don't know the ingredients but in true holistic faith you feel better. 
 

Ha. This is an awesome analogy, and having been a bodybuilder in the eighties/nineties, I know exactly what you mean! I often look back in regret at what I did with these plugins much as I have at what I once consumed in the name of fitness.

Well the input and output meters tell you everything. The level entering and leaving the plugin. Once you are in the territory of calibration a 0 dB VU ref on a VU meter to a digital reference like -14, -18 or -20 then VU's all tell you a lot. They suddenly mean something.
 
Nothing wrong with pushing everything in your system way down lower level wise in order to prevent clips anywhere but also just to ease everything off and provide lots of dynamic headroom.  But you can go maybe a little too low then you are not even engaging things like CLA properly in oder for them to do what they do.  They are very level dependent plugins and you need to be very aware of what the rms level is running through any of them.
 
Test signals are very handy.  I have some links to them here from my Google drive.  These are both pink noise and a sine wave at the -20 ref level.  So for other ref levels either add or subtract gain.
 
Pink Noise file:
 
https://drive.google.com/file/d/0B_2Jb7O_b5BkanhGUmlTdXZzeXc/view?usp=sharing
 
Sinewave file:
 
https://drive.google.com/file/d/0B_2Jb7O_b5BkdjdzOHpmSzNvc1k/view?usp=sharing
 
Studio One can generate test signals.  But it is good to get them and use them for level checking purposes.  These are stereo files and best put onto stereo tracks. 
 
If you put a VU meter on these calibrated for -20 then the VU will show 0 dB VU for the sine wave and about -1 dB VU for the pink noise.  The slight level drop for pink noise is normal for this type pf signal. 
 
With CLA this signal should be about 2 dB shy of the calibrated level for -18.  So the input meter should read -2 db VU. Crank the input signal up by 2 dB to get it to 0.  The output meter should be also be showing 0 dB VU.  With music the GR for me anyway is exactly as he suggests between -2 and -3 dB all the time.  From there you fine tune the processors.  It is not magic but a simple set of processors all set up to do a certain job.  Compression and saturation etc.. It is good that you can fine tune some elements of CLA.  I like backing off the drive a little for a cleaner sound over a mix.  But with CLA on the right type of buss for example it could add some real saturation.  The tone controls are just there to fine tune your EQ as well.  Don't go mad with those.  If your mix is good they should be pretty flat. 
 
K-12 is too loud a ref level to be working at in general.  Especially for your DAW sessions.  It has the poorest headroom sound or transient sound on that front.  You also have to be on clip alert too at this ref level.  K-14 is only a little better on that but still better.  (K-14 is excellent for me as my Yamaha digital mixer is all calibrated for this level so everything is perfect inside that at -14) K-20 is excellent for transients and headroom.  Everything inside my digital mixer is now 6 dB lower.  Easy to convert a pre mastered K-20 mix up to any mastered value.  Such as K-10 for a super strong master that is still punchy.  But this is not required so much now though.  As things like iTunes will turn them down anyway.  Better to aim for a K-14 rms mastered level these days as that translates real nice to around -16 LUFS which is perfect for iTunes and many other streaming sites etc..
 
 
 
 

Agreed...
 
I should say I aim for at least 12dB RMS average for the final mix. Even though some stuff has came out at -8 ish because of adding extra punch in the master.
 
For mixing levels, I actually start of quite low around -23 dB to -20dB reference level so I know I have plenty headroom later on. I live, learn and forgotted.
 
 

OK that is very good. Mastering around -12 is very nice indeed. I have found from studying some real nice Steely Dan masters at -10, can also sound pretty stellar as well.  Rather loudish though but still punchy and transient.  I rarely go higher than this now.  I use the DR meter to keep check.  I aim for a mastered rms level that shows up at least a DR of 10 or 11.
 
I have pushed for -8 on some tracks within album masters I have done only at the mercy of the client artist. Not me. I would not have done it myself.  They were chasing very loud commercial CD's.  Things like PSP Xenon have to work real hard under these conditions and I don't think we should put our limiters under that much stress.  Once you shoot for -12 or -14 as a mastered level the limiters are suddenly having a much more relaxed time.
 
Anyway I hope our friend ubershep can find his way around why he has not got enough signal rms level hitting his CLA. It is important to be going into this plugin at the right level. It is expecting it.  He has got the opposite issue.  Not enough signal level. 
 
 

That looks like an interesting plugin to get.