I’m sure you have already heard parallel distortion, even if you don’t know what it is. Yep, it’s that common; it’s present on all kinds of recordings. You would be surprised how many different genres have been treated with it. And yes, I would be surprised, too. So what is parallel distortion, and why do we use it in mixing?
It’s additional distortion, which means you add it on top of your original tracks, instead of modifying them directly. Exactly the same way you treat most reverbs or parallel compression. It means that in a DAW you would send your tracks to a separate AUX track with a distortion plug-in, or go into an outboard unit. Another method is to use the built-in wet/dry control of he plug-in or the outboard device.
The goal is to be able to set the ratio between the original track and the effect. That way you can always get just the right amount of distortion, without going overboard or having to change the frequency response and dynamics of the whole track. Of course the resulting sum of both tracks will have a modified frequency response and dynamics. But at least you can say you have tried, hey? It also enables you to use your pristine clean preamps and/or cheap interfaces, and dirty up the signal to turn it into the right kind of old school mess with using parallel distortion.
Using parallel distortion is actually not all that old of a technique. Back in the old days (a couple of decades ago), distortion was all over the place without really having to add it on top of anything. Pretty much every outboard gear produced some kind of harmonic distortion. Transformers, tube and discrete transistor circuits, and tape all added their own signature to the sound. But things kept getting cleaner and flatter. Or more boring, unexciting and colorless, if you will. So a new need emerged for adding the color back to the music, in the form of harmonic distortion. It resulted in all kinds of purpose built plug-ins and outboard gear. As a neat trick, you can even use guitar pedals as well, with the right interface that corrects your impedance mismatches.
You get tube style, germanium transistor style, transformer style, elephant vibrator style and who knows what else kind of distortions. And of course it’s a scam as well, because lately you have to have some spicy parallel distortion going on on everything, or you’re not cutting it as a pro anymore. The truth is, if you keep churning out great sounding tracks, no one will care if you’ve used parallel distortion or you have recorded stuff exactly the way they hear it in their speakers.