The rhythm of algorithms
These days, limiters often employ selectable algorithms to better suit your individual music, some of which deploy sophisticated multiband technology under the hood. Take some of Ozone’s venerated IRC algorithms, for example.
IRC stands for “Intelligent Release Control”, and to some extent, IRC will preserve the dynamics and overall clarity of your mix. Now, with so many different IRC settings—four overall, with separate “styles” in IRC III and IRC IV—it can be tough to know which is best for the music at hand. Luckily, most companies offer manuals to explain their algorithms, and iZotope is no exception, providing a detailed explanation of IRC in their documentation.
Where does multiband come in? That would be IRC IV, which uses a multitude of bands, rather than three or four, as you would’ve seen in the conventional, multiband limiters of yesteryear. IRC IV’s bands are split up in a psychoacoustic way to better serve the material at hand, resulting in a more transparent and natural effect.
All of this is well and good, but how do you actually use you a limiter to your advantage? After all, if set wrong, limiters can introduce their own distortion, as well as unpleasant side effects on the groove.
How to hear the difference in 4 easy steps
Here’s a step-by-step guide for identifying for tuning your ears to the sonic specificities a limiter imparts on your mix. I usually go through some iteration of this process every time I demo a newly-released limiter.
1. Link the limiter’s input and output as you tweak
Many limiters allow you to link the input gain or threshold control with the output ceiling, so that as you push one, the other comes down in level. This way, your ears won’t be fooled by a satisfying jump in loudness, and you can better judge the moment you’ve gone too far.
Ozone 8 has a linking feature that pairs the threshold slider to the ceiling. Turn that on as you pull the threshold down. At some point, you’ll hear audible distortion. Stop here and pull back until you don’t hear the distortion any more. Now you’re ready for step 2.
2. AB between gain-matched bypass and limited signal
Compare the limited signal with its bypassed variant, carefully noting the differences in timbre. Does the track feel narrower with the limiter on? Are the transients pillowy, softer, or otherwise altered? Does the groove of the whole piece seem different? Note your generalized findings, and write them down if that helps you (it helps me with internalization).
3. Set up a delta test
This is where things get fun—and depending on the limiter, a bit tricky. We’re defining “delta” here as the real-time difference between your limited mix and bypassed version. It’s similar to soloing the esses of a de-esser (where you’d only hear the ess), or the noise output of a de-noiser (where you’d only hear what it’s removing).
Isolating and soloing these artifacts will call attention to them. Hearing them apart from the mix will tune to your ears to what’s missing from your limited material once you switch it back on. It’s a bit like training yourself to hear the effects of MP3 encoding using Ozone’s codec simulator: Once you hear what the encoding takes out of the original mix, those weird, lossy qualities of MP3s reveal themselves more plainly. The same general principle underscores this exercise.
Some limiters offer specific delta parameters, but not all do. Luckily, you can make your own with some clever routing, multiple instances of a limiter, and a plug-in that flips polarity.
Please note: different DAWs handle latency in different ways, so you may need to experiment for your own purpose. Luckily, the workflow is roughly the same in Logic Pro X and Pro Tools, two of the more common DAWs.
First, kill the output of your source track, selecting “no output” (or whatever variant of that terminology your DAW provides) in the output section. Next, route the source to two auxiliary channels on two sends. Duplicate the limiter to both auxiliary channels, and bypass the limiter on your source track. On the second channel, flip the limiter itself into bypass. Logic users take note: Do not use your DAW’s global bypass, but rather, the plug-in’s own bypass parameter.
Next, load any utility plug-in after the limiter that flips the phase of the left and right channel.
Logic users, I cannot stress this enough: it’s essential for you to have both limiters instantiated for the trick to work, or else latency will be an issue, and you won’t hear what you’re supposed to hear—the sporadic limiting of your mix, usually on the kick and snare drums, when the limiter is audibly pushing down on signal.
By way of example, here’s a snippet of music:
And here’s it’s delta/difference signal:
Once you’ve analyzed this for a while, you’re ready for the next part:
4. Go back to the A/B comparison
That’s right: Go back to step two and compare the limited mix to its bypassed counterpart. Now that you’ve identified, heard, and internalized what the limiter is taking away, you should be able to hear the differences between the two more clearly. Start moving parameters around, and you’ll find you’re hearing what they’re doing; less guess work will go into tweaking the limiter’s time-constants and stereo interdependence options, because your ear has tuned itself to what the limiter is taking away.
Limiters are getting better and better all the time. Some are quite revolutionary—Ozone 8, for instance, employs an assistant which intelligently sets your limiter, and goes farther by placing a dynamic equalizer before the limiter which helps achieve an even more transparent operation. This tool has already found its way into the rig of at least one respected mastering engineer.
The larger point is this: As limiters are changing all the time, it’s important to understand their base functions, and also, to find ways of testing limiters you may want to purchase in the future. It is my hope I have provided you with the necessary tools to do so in this article.