I know a little about harmonics. Probably not enough. It seems we can now add both odd and even harmonics to individual tracks in a mix. Actually it isn't recent since adding harmonics though old hardware is something that's been happening either knowingly or unknowingly for some time. Obviously harmonics isn't restricted only to electronic circuitry and affects pretty much everything we hear.
I think the difference now is we can become selective in the harmonics whereas in the past we were left with the effects of whatever mixing board or or preamp we happened to be using. Take Waves Scheps Omni Channel for example, it gives you the option to add either even or odd harmonics to a track and adjust the sensitivity. In my thinking, the even harmonics seemed the most desirable, yet they can also reinforce frequencies we don't want to reinforce. A good mix of even harmonics can help to add an airy cushion of warmth to a track if it is done using the correct harmonic relationships.
My guess is that the uneven harmonics come in handy for those off color chord shapes or unusual darker frequencies. Maybe to add a feeling of dissonance. Or maybe to balance the effect of too much even harmonics.
I'm wondering if anyone here approaches a mix looking deeply at the harmonics of it and how you use that to an advantage?
I do, but in a more automatic and random way lol. So I start a composition or mix, and the first thing I decide is console emulation using Wave's NLS which gives three flavours of harmonic distortion. Although, and I've just spent an hour or so trying to determine this, I was under the impression that the Neve emulation was tube based, and I don't think it is...meaning you get three odd harmonic distortion choices. It doesn't matter, because each module does have a different flavour. So for me, I will choose the TG12345 emulation for pop or a mid 60s sound. The TG12345 has a slightly metallic sound, that can be further enhanced by using the TG12345 channel strip plug in conjunction with the NLS. The SSL module is the clearest of the three modules, and I would use this for a really big mix...50 tracks plus. The TG12345 can make the low-mids a bit woofy, and in a big mix it can make clarity or separation between tracks hard. The Neve is in-between option. I use this module as my classic rock module.
Now, this is only layer one of the harmonic distortion mix. Next, depending on the instrument another layer of harmonic distortion is added. For electric guitars and vocals, I use Sonar's very un-flashy tube pre-amp emulation. This adds in a layer of 2nd harmonic distortion. Basically, I'm following the rock avant-gardes' signal flow on their classic recordings. If you do some research, up until the mid-60s...there was only tube based audio recording technology. I'm not sure when, but The Beatles first replaced their tube based Vox amps with transistor based ones...their sound changed. It seems this was in 1966. What Oasis called The Beatle sound was in fact, a tube mic recording a transistor based amp and being fed into before 1969 a tube based desked, and after 69 a transistor based desk.
On other instruments, particularly orchestral or drums I will use tape sims. For orchestral instruments, I tend to use the J37 tape sim from Wave's, which I think was tube based and on drums I like the really plain tape sim on the prochanel.
On the mix bus, I always use Wave's Kramer Master Tape, which I know is a tube based tape machine.
So you can see how I approach a mix from a harmonic perspective hopefully.
It's much more detailed than this...but hopefully you get the drift.
You can hear what I am talking about on my last work, a cover of Nights in White Satin https://www.youtube.com/watch?v=3XcQVCAJakM
my harmonic technique is all through this work!