Harmonic Distortion: Myths vs Reality
Harmonic distortion isn’t just even vs odd harmonics. Discover how saturation shapes your sound and choose saturator plugins that actually help.
The lie about harmonics
For years we’ve been sold the idea –which I totally bought into– that the “character” of saturation is all about the harmonics.
When I started actually measuring and analyzing real analog gear in a kind of “linear” way –looking at the harmonics and their amplitude across the spectrum– and then tried to replicate that in plugins, I was seriously disappointed.
Those early prototype plugins ended up sounding like NOTHING, Nada, Zero. I was measuring hardware that had THD around -50 dB, sometimes even lower, and it sounded warm, full, musical and colorful. My plugins, on the other hand, sounded cold. I could barely hear any difference. It felt like the plugin was bypassed. To start hearing anything resembling a change, I had to push those harmonics or the THD up to around -20 dB even more… just to get a tiny bit of movement.
Copying the “shape” of the harmonics was not enough to recreate the sound.
“But I do hear harmonics”
And that’s fair. You can hear harmonics, especially with simple material: pure waves, isolated notes, single instruments, synths, etc. That’s where harmonics are the most obvious and easy to appreciate.
What I’m getting at is this: the more complex and layered the audio is (mixes, buses, stems), the more those harmonics tend to get masked. You don’t clearly hear them one by one anymore... but you still perceive their effect.
So what is it that we’re actually perceiving?
Our ears react much more to how the waveform behaves over time than to a list of harmonics in a graph. And I’m not just talking about level on transients or sustain, but about the shape of the waveform over those few milliseconds, and how that shape changes across different parts of the spectrum.
Saturation doesn’t behave the same way at all frequencies. Those tiny time shifts and changes in shape are what create that pleasing effect we sometimes hear in high-end gear when you push it a bit… and even when you’re barely pushing it.
Clipping: when the signal gets slapped in the face
Clipping is the most brutal version of all this: the signal tries to keep going up and the system basically says, “that’s as far as you go.” The top of the waveform gets chopped off, a bunch of new harmonics show up and, if you really overdo it, you’ll get some lovely aliasing on top of that… I talk more about that in this article about aliasing. What we usually describe as “broken”, distorted, overdriven, is very often clipping in one form or another.
There are different flavors of clipping: some have a softer transition into distortion, others hit the ceiling hard and abruptly. It all depends on the circuit, the components and how it’s designed. But in every case, it’s still part of what you’re perceiving: how the peaks are being reshaped, and how that violence is spread over time and across the spectrum. This topic really deserves its own dedicated article, so I’m just touching it lightly here to set up the concept.
The myth of even vs odd harmonics
We’ve also been told that “even harmonics = tubes” and “odd harmonics = transistors”. I don’t know exactly where that came from, but it’s really not accurate. And yes, I believed that for a long time too.
When you really push a tube stage into heavy saturation, the waveform starts looking more and more like a square wave. And square waves are made up mostly of odd harmonics.
Even harmonics usually show up when there’s some asymmetry or DC offset in the waveform, and a lot of that can be adjusted or reduced with things like biasing, feedback, etc.
So, back to a mix context: if you just “artificially add” even or odd harmonics to a complex mix, you’re not going to get a big audible difference unless those harmonics are at pretty extreme THD levels (around -12 dB or so). And at that point, we’re no longer talking about “subtle color”, we’re talking about obvious distortion.
What kind of saturator should I use?
It all depends on what you want and what you’re feeding into it.
Personally, I like adding a subtle saturator on each bus in a mix, plus one on the mix bus. And on individual tracks, where it makes sense, I’ll use something a bit more aggressive, flirting with clipping if the context calls for it.
A bit of mojo almost never hurts: it tends to make mixes sound rounder and more glued together.
But a lot of times we start stacking saturators –even “subtle” ones– and the mix actually ends up sounding worse. That’s where how we choose our plugins becomes really important.
How to choose saturator plugins
You’ll hear people say “all plugins sound the same”.
To me, that usually means one of two things:
- They’ve mostly used very generic, heavy-on-marketing products with boilerplate algorithms pulled from public code snippets.
- Or, honestly... they’re just not listening very carefully (and I mean that in the kindest way 😄)
I’d say well over 90% of saturator plugins out there are not that great, and a lot of them are backed by really strong marketing. That’s part of why plugins got such a bad reputation for years. Which is a shame, because there are small developers and big companies doing really good work.
So, how do you actually pick your saturators?
Short version: don’t rely only on pretty graphs and marketing copy.
- Download the demos.
- Test them on different kinds of material: vocals, drums, buses, full mixes.
- If you care about the harmonic content, sure, analyze it – but don’t stop at the numbers.
If, on what’s supposed to be a “subtle” plugin, you see a pretty high THD reading, say around -15 dB of THD, chances are it’s just another generic saturator… although not always. It could also be well-designed and that THD might actually be musical. That’s why you need some judgment when you analyze plugins this way.
So let’s get straight to the point:
If you want saturators to add subtle warmth, look for plugins that:
- show low THD at normal working levels,
- but still make an audible difference to your ears,
- make the mix feel more alive and connected, without turning everything to mush.
Because at the end of the day, beyond graphs and myths, that’s what really matters:
If a plugin with low THD still makes the sound move you more, then it’s doing something right.