Multiband transformer saturation, explained

Push a signal through an audio transformer and its iron starts to saturate. It adds harmonics, weight under the sound and a density that holds a mix together. Transformers saturate more as the level rises and the frequency falls. That is why you notice it first in the low end.

That is the problem with saturating the whole signal at once. The loudest part of the mix, usually the bass, decides how much everything gets. Drive it hard enough to thicken the mids, and the low end turns to mud.

Split the signal into bands and you can drive each one as hard as it needs. Weight under the kick and bass, density in the mids, and an open top. The catch is that separate bands can stop sounding like one piece of gear. A good multiband saturator lets you pull them back together.

1. Put IS-1 on a mix bus, a master or a single instrument. It opens with four bands. Click the bar above the frequency scale to add one, and drag a crossover to move it.
2. Raise Drive on the band you want heavier. The level is compensated, so you hear the character change, not the loudness.
3. Set Iron for how much saturation that band gets. The spectrum shows where it lands. Each band's meter shows the band's level next to its saturation.
4. Raise Lock to make the bands saturate together, like one transformer.
5. Turn up Observer to pull the saturation back wherever you would hear it.
6. Switch on Delta to hear only what the iron adds.
7. Choose the Phase. Linear keeps the band edges in time but adds latency, so it suits a master. Minimum adds no latency, so it suits tracking.

IS-1 is a multiband transformer saturator for Mac and Windows, with one to eight bands. It has a 30-day free trial.