[alexeymohr]

We're all getting too far away from the question here. Obviously the best answer is "mix it right."

But the question wasn't about that. It was specifically about whether or not any of these plugins could process splits. Clearly they cannot. I've contact both iZotope and Nugen and they confirmed that their plugins cannot do this.

The current remedial solution, when slight adjustments to the mix itself are not an option for whatever reason (if you're the transfer or layback tech and not the mixer), is to measure the composite mix stem and apply precise corrective clip gain to all the stems based on the measurement (if it's -23.5, then reduce all stems by 0.5dB. If it's -24.7, then add 0.7dB of gain).

Of course when applying negative gain this pulls your peaks down which isn't great, and when applying positive gain this probably pushes your peaks out of spec which then requires another limiting pass. Also not great.

The better answer is for the mixer to take the same measurements, then make adjustments to VCAs that sit upwind of the limiting. But if these VCAs control individual mix tracks which live before the respective chains that contain any kind of dynamics (or even significant EQ for that matter), then there will be some amount of guess-work and trial and error involved as 0.1dB of pre-chain VCA trim ≠ 0.1dB of change in the level of the final stem in the majority of cases.

Better still is to simply instantiate AAX trim plugins just before the final true-peak limiter in any given master path and use those to make the fine-tuning adjustments to guarantee spec.

So these workflows already exist. The question was simply whether or not any of the purpose-built auto-leveling plugins were actually useful in a production environment where split stems are required. The current answer is still "no."