Music Production: Double-Tracking & Doubler Effects

Doubling, whether recorded at the tracking stage or “faked” at the mixing stage, is a common technique in modern music production. If you're intrigued by learning more about doubling, you've come to the right place!

In this article, we'll dive into both strategies for achieving the doubling effect in our mixes, discussing how doubling works, why you may want to use it, and the pros and cons of either method.

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A Primer On Phase

In order to fully understand how doubling works, we need to understand phase.

Phase, at its simplest, refers to the position of a point in time on a wave cycle. For a repeating waveform (like a perfect sine wave), the phase will cycle from 0° to 360° (or 0 to 2π radians) across a full cycle.

This cycling and phase can be visualized in the following graph:

In mixing, however, the term phase generally refers to the alignment of positive and negative amplitudes between non-identical waveforms. This is largely due to the fact that sound waves and audio have complex waveforms (made of many different frequencies with many different amplitudes over time) rather than simple, repeating waveforms.

The more aligned two or more waveforms are, the better their phase alignment.

Two perfectly identical waveforms can be said to be completely “in-phase”, while two perfectly identical waveforms in opposite polarity can be said to be completely “out-of-phase”.

As an aside, flipping the polarity of a signal is different than altering its phase (which is dependent on altering the timing of the signal).

When two signals of equal amplitude are perfectly in phase, their output will be double that of either signal.

When two signals of equal amplitude are perfectly out-of-phase, they will completely cancel each other out and there will be no output signal.

Anywhere in between perfectly in-phase and out-of-phase will cause some amount of phase cancellation, which will effectively result in “notches” within the frequency spectrum of the output. If the phase differences between these signals are modulated (the timing difference is modulated), the frequencies of these “notches” will move over time—this is the case with modulation effects such as chorus and flanger.

But when we're tasked with doubling, we won't have perfect duplications of our audio signals. Even if a musician were to perform two seemingly identical takes, I guarantee there would be differences between the two recorded audio signals.

These differences (in timing, pitch, note duration, noise, etc.), however minor they may be, cause differences in phase, which in turn give us a sense of doubling rather than a simple increase in amplitude.

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Reasons To Use Double-Tracking Or Doubling Effects

Doubling has become such a common music production technique for a few reasons.

First of all, having a doubled track helps to add sonic richness to a performance. The small differences between the two performances, when mixed together, thicken the otherwise single track, adding weight to the sound. We can enhance the sense of depth with doubling and, when we opt to pan the tracks, a sense of width.

The stylistic effect of doubling can make a performance sound “larger than life” as a seemingly single musician can be effectively heard twice.

In terms of contrast and movement within a mix, doubling can be used to enhance certain sections or even certain syllables versus an otherwise single track.

For example, a verse vocal may be single-tracked for conciseness, while the chorus vocal may be double-tracked for additional space and weight in the mix. As another example, we may only want to double the last few syllables of each line in a verse to add emphasis to the rhyme scheme.

I should reiterate here that doubling requires a performance as close as possible to the original. Adding harmonies and ad-libs are incredible production techniques on their own, but don't fall into the specifics of doubling that we're discussing in this article.

In most cases, double-tracking is preferred, as we'll get two different performances, each with its own subtle nuances.

When double-tracking isn't possible (sometimes the case during mixing once everything has been recorded) and we want that doubling effect, we can reach for doubler effects to achieve similar results. Changing the timing slightly with delay, the tuning with detune, and the panning can alter the duplicate enough to achieve a similar effect as double-tracking. Adding some amount of modulation can help bring out some more nuance, though it likely won't be as nuanced as proper double-tracking.

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Beyond Doubling (Tripling, Quadrupling, Etc.)

If doubling a track can give us greater depth, weight and width than keeping a single track, it makes sense that adding more layers would yield more depth, weight and width.

Tripling, quadrupling, and so on are certainly techniques worth considering for giving a performance additional size and dimensionality within a mix. However, these strategies quickly reach their point of diminishing returns and often give us the opposite result from what we'd expect.

It really comes down to the differences in phase, timing and tuning between the different tracks being mixed together.

Remember that, with doubling, the sense of dimensionality comes from such phase differences. The slight differences in timing act almost as a pseudo-delay-type effect, only with changing delay times. These slight pitch variations, however minor, act almost as a chorusing effect. Mixing the two together will allow for additional depth and dimension, even as some frequencies are momentarily reduced in level due to phase cancellation (and other frequencies are momentarily increased in level).

The more additional takes we mix together, the more phase differences will interact with each other. In some cases, this can be a good thing, as it adds character to the sound.

However, we'll quickly reach a point (often as soon as we start tripling tracks) where the timing differences will smear the transients of the intended performance, the phase issues caused by pitch differences will mask the true timbre of the intended performance, and the “larger than life” effect we intended to produce ends up sounding a poorly-defined mess.

A common example of this is with heavily distorted electric guitars, which are often doubled and panned to opposite sides of the stereo spectrum. However, when we get into quadrupling (or more), we can quickly smear the transients, and the already-saturated harmonics of the guitars often blend into an ill-defined, heavily masked sound.

In some cases, tripling may sound better than doubling, especially if the double-tracking (or doubler effect) is tight and there is panning involved. However, in most cases, I'd recommend simple doubling. It's easier and generally gets us that weighty, dimensional sound we're after with greater clarity.

I encourage you to try adding more layers to your tracks and making your own decisions on what sounds best. Throughout the rest of this article, I'll focus on doubling, though what I'll be writing about can also apply to tripling, quadrupling and so on.

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Double-Tracking

We've already touched on double-tracking with some detail, but now let's dive a bit deeper.

As the name suggests, double-tracking is the doubling of a performance during recording. More specifically, we'll want to re-record our preferred take as closely as possible (harmonies can yield a similar effect, though they aren't truly considered double-tracking).

Even if the performer nails the timing and tuning of the first and doubled takes, there will surely be small differences in the audio signals. These differences give us the doubling effect.

From there, we can mix the two signals together. Here are a few thoughts to consider:

• Will both tracks be mixed at the same level, or will one be mixed lower than the other? Having both tracks relatively equal in level will maximize the “size” of the doubling effect, whereas having different levels can potentially yield a greater sense of “depth”.
• Will the tracks be centred, panned to the same side, or panned to opposite sides? Panning them to the same direction, whether in the centre or off-centre, can enhance the sense of depth and direction of the doubled tracks. Panning the tracks apart can enhance the width of the tracks in the mix. How far should the tracks be panned apart, if so?
• Will the phase differences in the low-end frequencies be problematic in the representation of the tracks? Sometimes it's worthwhile to high-pass filter one or both tracks to avoid an ill-defined low-end in the elements and the mix as a whole.
• Should the tracks be doubled throughout the entire mix, or does intermittent doubling serve the production better? Consider doubling or undoubting entire sections or even certain lines within sections. Emphasis, dynamics, and movement are important!
• Are the two tracks close enough in timing and tuning to warrant their use in achieving the doubling effect? Perhaps we might need timing and tuning editing to bring them closer together. Alternatively, we may want to use a dedicated doubler processor/effect to achieve the doubling effect, which we'll discuss next.

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Doubler Effects

Doubler effects aim to recreate the double-tracking effect by duplicating an audio signal, manipulating it, and mixing the two signals together. These units often combine various effects together in order to vary the duplicate(s) from the original.

Some common processes included in doubler effects include:

• Delay: a short delay time between the original and the duplicate will alter the phase and provide a pseudo-double-tracking effect at the expense of comb-like filtering.
• Detuning: minor detuning will alter the waveform of the duplicate (and/or original if applicable) and provide a slight chorus-like effect.
• Panning: many doubler effects will allow us to pan the original and duplicate(s) around the stereo panorama as we see fit.
• Modulation: the option to alter certain parameters over time (often via an LFO) in order to add dynamic changes to the differences between the track versions over time—this can help tremendously in approximating the actual double-tracking production technique, which has much more nuance than simple duplicating and processing a “doubled track”.
• Gain: to mix the levels of different versions of the track together appropriately.

My go-to plugin for doubling is the aptly-named Waves Doubler:

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Common Use Cases For Doubling

Now that we understand doubling and the two methods of achieving doubling in our music productions, it's time to consider a few common cases for using the effect in our mixes. In this article, we'll consider doubling the following elements:

• Lead vocals
• Background vocals
• Electric guitars
• Acoustic guitars
• Auxiliary percussion
• Lead elements

Doubling Lead Vocals

Double-tracking lead vocals is one of the most common vocal production techniques and is used in many genres.

While there are no hard rules here, it's often the case that the lead vocal is panned to the centre, and the double is mixed just underneath it (also panned to the centre). This helps add weight and depth without seeing the stereo image of the lead vocal, which is generally mixed up front and centre in the mix.

When doubling a lead vocal, we can opt, stylistically, to double-track the entirety of the song. However, this can reduce the overall movement of the mix. In many cases, it's better to periodically introduce the doubling of the lead vocal to make sense of the long-term dynamics of the song.

For example, we can:

• Double certain sections and not others.
• Double certain phrases or words and not others.
• Adjust the mix of the doubled versions of the lead vocal throughout the mix.
• Add panning and additional layers to achieve width in certain sections or certain words.

By doubling vocals, we can achieve a sort of “larger than life” effect where a single vocalist seemingly has two voices.

Doubling Background Vocals

Background vocals are often doubled as well, in addition to their usage for providing harmony and counter-melody for the lead vocal (and even different vocal lines than the lead vocal).

A common technique for making space for the background vocals around the lead vocal is to pan them. If we want really wide background vocals to really separate them from the lead vocal, we can consider hard-panning doubled background vocals to opposite sides of the stereo panorama.

For example, we could have a third-harmony and an octave-harmony background vocal performance, double-track both of them and hard-pan the first versions to the left and the second versions to the right. This way, we'll have nice, full, wide background vocals (as opposed to hard-panning the third harmony to one side and the octave harmony to the other, by themselves).

But even if we aren't hard-panning doubled background vocals to opposite sides, doubling a background vocal and panning them together can help add depth and directionality to that vocal.

For example, we can have a different vocal line for the background vocals panned slightly off-centre with its double panned to the same direction. This way, the background vocal will sound like a distinct source with a specified location in the stereo panorama, all while having the enhanced depth that comes from doubling.

Background vocals are often layered, and adding doubles, triples, etc., can quickly wash them out. For that reason, I advise time-aligning your background vocals. It helps make them sound tighter and more professional by reducing transient smearing, inconsistent tails and other timing issues. The added clarity and intelligibility are well worth it.

You can opt to edit the timing of your background vocals manually by cutting and nudging (don't forget to crossfade) and time expansion/compression.

Alternatively, you can save tremendous amounts of time and frustration by investing in a tool like Synchro Arts VocAlign, which is my go-to tool for time-aligning vocals (among other things).

Doubling Electric Guitars

Electric guitars (especially distorted electric guitars) are often double-tracked and hard-panned. In harder genres (or any genre, for that matter), this technique helps to get them out of the way of the typical centre-panned elements (kick, snare, bass, vocals) while adding thickness and width to the guitars.

This technique, as with practically all doubling techniques, is best achieved through proper double-tracking rather than with doubler effects. Pay attention, when tracking, to ensure that the timing and tuning are locked in, as poor phase relationships on distorted guitars can quickly ruin their clarity—this is, again, why quadrupling (doubling on the hard-left and hard-right) typically worsens the sound of distorted guitars versus simple doubling.

In terms of clean electric guitars, the same technique is often used, though we may be able to get away with slightly more differences between the doubles, as their harmonic profile is less robust and their transients are better defined.

Doubling Acoustic Guitars

Acoustic guitars, by themselves (think singer-songwriter stuff), are often best left single-tracked. However, doubling acoustic guitars can sound amazing, especially when they're panned out from one another to give some width.

Doubling Auxiliary Percussion

Shakers, maracas, tambourines, and other auxiliary percussion can add subtle movement and nuance to a mix. In addition to such movement, we can often add subtle width by doubling them (with double-tracking or doubler effects) in the mix.

Doubling Lead Elements

Lead elements, whether it's the lead vocals or an instrument taking a solo, can be emphasized and made to sound bigger with simple double-tracking (or the use of a doubler effect).

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Related Questions

What is multitrack recording? Multitrack recording is a method of recording sound as audio with multiple tracks or channels that can then be processed individually and mixed together into a final mix. This type of recording is standard and often taken for granted in modern times, though it was only developed in 1955.

What are audio modulation effects? Audio modulation effects manipulate the input audio over time via the control of a carrier signal. The input audio is referred to as the modulator signal, which technically controls the carrier signal, which is generally produced via an oscillator generator or signal detector.