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How to Mix Harmonics

When mixing harmonics, you can use differing harmonic formations to separate similar or competing signals. Additionally, harmonics can be used to add high-frequency clarity when the harmonics are higher in order, or low-frequency fullness and warmth when the harmonics are 2nd and 3rd order.

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Understanding Fundamental and Harmonics

For this video, the chapters are in no particular order. Also, I’ll mainly be using Melda Audio’s free Saturator plugin for this video, so feel free to download it if you want to follow along.

If you want to understand how to mix with harmonics, it helps to first understand what harmonics are - every signal has a fundamental frequency or its lowest frequency. Harmonics form in relation to this fundamental and are multiples of the fundamental frequency that greatly impact a sound’s timbre.

The fundamental is called the 1st order, 1 multiple above is called the 2nd order harmonic, 2 multiples above the fundamental is the 3rd order harmonic, and so on.

Aside from changing the timbre, harmonics fill out the frequency spectrum making a signal sound fuller, so let’s observe this by listening to a signal with and without added harmonics.

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Harmonics and the Phantom Fundamental

Harmonics play one other crucial role, that’ll be important to your mixes, albeit in a more obscure way. Harmonics cause a psychoacoustic phenomenon in which the fundamental frequency becomes easier to hear - in fact when we hear multiple harmonics, our brains automatically generate the fundamental, even when it’s not there.

This is important to listeners playing your mixes over smaller speakers - since these speakers often attenuate the lowest frequencies or the fundamental.

To illustrate this, let’s listen to a sine wave with harmonics, and then attenuate the fundamental - when attenuated we won’t be able to physically hear the fundamental, but its key or note will still be apparent.

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Blending Even and Odd Harmonics

Now that we understand harmonics a little better, let’s talk about how they can be combined amongst multiple instruments. Each harmonic that’s up space in the frequency spectrum, meaning we can use variations of them to blend similar instruments, for example, our kick and bass.

If the 2 have fundamentals at the same frequency, we could create an even-order harmonic on the bass, and an odd for the kick or vice versa to help differentiate the 2.

Let’s listen to 2 competing signals, processed with differing harmonics.

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Tuning with Harmonics and EQ

Since even ordered harmonics are always doubles or even multiples of the fundamental frequency, they’ll always be in tune. For example, if the fundamental is C2 or 65.4Hz, then a 2nd order harmonic will be C3, or 130.8Hz - while a 4th order harmonic will be 261.6Hz and so on.

That said, if we want to emphasize the in-tune nature of a signal, we should add even order harmonics. Let’s take a listen to that.

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Emphasizing Kick with 2nd Order Harmonic

Carrying on with the idea of even-order harmonics, if we want our kick or bass to be super full, warm, thick, or any of those adjectives we should distort or saturate it with a 2nd order harmonic. Since this is the lowest possible harmonic, it’ll occupy low frequencies.

Let’s listen to a second-order harmonic added to a kick drum, and notice how it makes it a lot more impressive.

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Clarifying Vocal with High Order Harmonics

You may have heard of an exciter plugin before - what it does is add high ordered harmonics and a high pass filter, in turn amplifying high frequencies and adding a lot of clarity. I’ll use TAIP by Baby Audio to do this, and increase the presence to emphasize higher harmonics.

Let’s listen and notice how the vocal has more high-frequency content now.

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Experimental IR Harmonic Reverb

This next chapter is a bit experimental so bear with me here - in short, I’m going to create reverb using white noise, EQ that emphasizes harmonics, and a convolution reverb plugin. After I generate white noise, I’ll use an EQ to emphasize potential harmonic frequencies.

To do this I’ll need to know the key of the song, for example, if the song is C Major, then all 7 notes shown here can be amplified, and the 5 that aren’t can be attenuated.

Once I’ve done this, I can export the white noise as a WAV file, and import it into a convolution reverb plugin, like Logic Pro’s space designer.

I’ll adjust the length, the volume’s envelope to get the reverb tail to sound the way I want it to, and maybe attenuate some high and low frequencies, before blending in the reverb.

So what we’ve done here is create reverb that emphasizes harmonics, creating all of the benefits of harmonics that we’ve previously discussed.

Let’s take a listen to this reverb being used.

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Creating Harmonics with Multiple IRs

Aside from the harmonics generated with plugins, analog equipment can create harmonics as well - except, whereas a plugin’s harmonics are mainly static or consistent, analog generated harmonics occur over a short amount of time and in turn have an ADSR - interestingly, this can be emulated with impulse responses.

Unlike the last chapter in which we only needed one impulse response, doing this takes multiple impulse responses. A company called Acoustica makes plugins capable of this - so let’s listen to harmonics derived from impulse responses, and see if we notice a difference.

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Harmonics and Aliasing or Fold-back

Although harmonics have many benefits when mixing, if they’re too high in frequency, they can cause issues. If a harmonic goes above the maximum supported frequency of our session, it will get replicated down the frequency spectrum and will likely be disharmonious, or no longer tied to the fundamental.

To avoid this, we can increase our session’s sampling rate or introduce oversampling.

Let’s listen to high-order harmonics with and without oversampling, and keep in mind the effect may be subtle.

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