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Stems That Sum to Final Mix

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Stems That Sum to Final Mix

Postby ITHertz » Tue Mar 05, 2019 11:04 am

Hi Folks,

I realise that this is something that has been asked before, however I can't find a good answer - is there a way to create stems that sum to the final mix including mix bus effects?

In particular, I was thinking about compression. Say, for example, that I have two "stems", a synth pad and a kick, feeding the mix bus. If the kick exceeds the compressor's Threshold then the combined kick/synth signal will be pulled down even if the synth signal on its own is below the compressor's Threshold. However, sending the synth signal through on its own won't trigger any compression.

Back in the June 2018 issue of SOS there was an article by Sam Inglis ("Pro Tools: Creating Stems") in which he says that

there’s a very simple way to generate true stems, in which each themed set of tracks is printed with master bus processing and its own share of any global effects. You simply solo all the drum tracks, and perform a Bounce to Disk on the main output, then un-solo the drum tracks and do the same for the guitars, then the bass, and so on.

Won't this method produce a different output with respect to dynamics?

Also, won't this apply to any other level-based effects (like tape saturation), that is, the sum of the signals going into the processer is going to produce a different output to the sum of the individual processed outputs?


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Re: Stems That Sum to Final Mix

Postby CS70 » Tue Mar 05, 2019 11:39 am

Yes you're right - it's not the same thing to send a stem to a compressor and mix with no further effects than to send the whole mix to the same compressor. Your example is good. Dont recall the article so it may be it meant something else?

On the top of my head a way to have complete stems would be to send the whole mix to two buses, one with the compressor and one not.. then using a "polarity reversal +summing" trick you extract the "difference", so that you could reconstruct your whole mix by the summing the dry stems and the difference track. Basically such difference track would represent all processing on the master bus.. but never tried and it's before lunch so I may just be having hunger-driven hallucinations :D
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Re: Stems That Sum to Final Mix

Postby Wonks » Tue Mar 05, 2019 12:14 pm

If it's just compression, you can have the full mix used as the side chain for the master bus compressor (so you need a compressor plug-in that will accept an external side chain), so the stems are pulled down correctly in reference to the main mix.

If you have other effects, then it becomes a lot harder to get it perfect. You could insert gain plug-ins around the other master bus effects so that you can raise the signal level slightly going into them and then reduce it by an amount that gets you back to where the original stem would be, so that you get a similar level of tape saturation (etc) effect as the whole mix, though you'd need to experiment a bit as you won't simply want to raise all the stems up to the master track level, as you'd overcook things.

Not sure if you'd ever get things sounding exactly how the master mix sounds compared to adding the individual stems, but if people wanted to use the full mix, they've always got that option available.
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Re: Stems That Sum to Final Mix

Postby DC-Choppah » Fri Mar 08, 2019 12:30 am

You can only do this by NOT using any processing that crosses your stem barriers. No master bus processing. No common sends that cross over the stem boundaries.

If you know going in that you are going to produce stems, then you just set it up the session that way.
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