Iron Oxide 4 is a tape emulation AU universal binary plugin. It's old school tape emulation. Unlike ToTape, Iron Oxide 4 doesn't present a realistic tape model with wide-range sound—instead, it traps in the sound in the lows and highs and lets you make it bark. This is the one for putting on isolated tracks and cranking out, hitting hard.
Also, you can blur out the tone with flutter which will help get away from the 'digital' sound too—and Iron Oxide 4 features a new control, Inv/Dry/Wet. How this works is, you can narrow down the tone to a focussed area that is saturated, and then mix this with dry signal as you might in Reaper. But it doesn't stop there: you can also add the Iron Oxide tone inverted, subtracting it.
What you get when you cancel out a saturated bandlimited tone is this: you're producing a mid cut, but the mid cut stops happening when the Iron Oxide section saturates. As a result, your tone cut lets through only the punch and impact, and pulls back the mud. This makes Iron Oxide 4 a really flexible, easily approachable tone shaper. If you're trying to heighten sound density it's a great way to intensify a frequency range, and if you want to amp up the impact it can do that with the Inverted range on inv/dry/wet. You can also dial in the area you don't want on full-wet, then subtract it.
Simulates tape speeds of 1.75 ips to 150 ips (.) and you can give a separate tape speed for lows and highs. This is really designed to act as a bandpass in a way more realistic tape sims can never do, it serves an entirely different role in a mix. I've never recommended use of Iron Oxide on the 2-buss or a final mix for it's too colored and vivid- use ToTape for that.