Double Tracking Vocals: Different Approaches for a Richer Mix
Layering your lead vocal with doubles can add thickness, color and lift to the most important element of any song; the lyrics and melody. We explore numerous ways you can achieve that rich vocal sound in your mix.
By Charles Hoffman
Doubling vocals is the process of creating additional versions of vocal tracks and mixing them in with the original. While this seems like a rather simple process, there’s a number of factors you need to consider when mixing vocal doubles. Executed well, doubled vocals can add serious impact, depth and presence to your lead vocals, allowing the lyrics and melody to come through even stronger. We’ll be exploring multiple ways you can double vocals to achieve that stereo width in your mixes.
There is no “correct” way to go about creating vocal doubles, but different methods yield different results. A pop mix may call for one type of vocal doubling, while a folk mix may call for another. You may also only want to apply the doubling effect on the chorus. Therefore, it’s best to have an assortment of mixing options at your disposal. This article is going to provide you with a handful of useful vocal doubling techniques that you can test out for yourself.
The Haas Effect
If you were to take your lead vocal track, duplicate it and pan the two hard left and right, you would simply achieve a vocal appearing dead center in the stereo field, albeit at greater volume. So, what’s going on? Why doesn’t this method of “doubling” the vocal allow the width and perception of stereo vocals?
When a sound wave from a sound source reaches both your ears at the same time, you’ll perceive the sound as having originated from in front of you. If the sound source is to your left side, it will take longer for the sound wave to reach your right ear than it will your left ear. Your brain is capable of deciphering this tiny time delay, which helps it to locate the origin of the sound in the space around you. When you pan two identical vocal tracks hard left and right, there’s no time delay between when the signal coming from the left speaker reaches your left ear, and when the signal coming from the right speaker reaches your right ear. Unintentionally, you recreate what happens when a sound source produces a sound wave directly in front of you.
To avoid this occurrence and make it seem like two vocals are coming from different directions, you need to introduce some sort of delay into one of the audio signals. To understand this in more detail, we need to take a look at the Precedence effect or Law of the First Wavefront as it is sometimes referred.
The Precedence effect dictates that when a sound is followed by a second sound separated by a time delay that is below the listener’s echo threshold, the listener will perceive a single sound as opposed to two unique sounds. The perceived location of the sound is determined by the first wavefront to reach your ears. When the wavefront from the second sound source reaches your ears, it still affects the perceived location of the sound, but its effect is suppressed by the first sound.
The Haas Effect is a psychoacoustical effect described in Helmut Haas’ Ph.D. thesis that is often equated with the Law of the First Wavefront. Most people in the music industry commonly refer to the Haas effect as the ability for humans to localize sounds around themselves.
The simplest way to create stereo width from a mono vocal is by duplicating the vocal twice, delaying the two duplicates, and then panning one duplicate hard left and the other hard right. The reason you don’t delay or pan the original signal is that you need it to act as the first wavefront and reach your listener's ears first, allowing them to localize the overall sound as coming from the center of the stereo image. If you keep the delay time of the duplicates short enough, this monstrously full vocal will be perceived as a single wide-spread sound, as opposed to three distinct sounds.
As you ramp up the delay time of the duplicate vocals, it will become apparent to the listener that the three audio signals are in fact three separate entities and not a single sound. There’s no hard and fast rule stating how much to delay your duplicate vocals, but make sure to delay each by a different amount to avoid ending up with some form of slapback delay that plays back like it’s in mono. For example, try delaying one duplicate by 10ms and the other by 20ms. An appropriate delay time is entirely source-dependent, so a delay time that works for the vocals in one song may not be suitable for the vocals in another.
The Basics of Doubling Vocals
Traditionally, the way to achieve doubled vocals was by “double-tracking,” meaning the artist would just record their lines twice. Sometimes however, the singer may not be available for additional recordings, you may be the hired mixer and be sent vocal stems that don’t include doubles, or perhaps the singer is finding it difficult to cleanly overlay the same vocal line twice. The production style may also warrant a clean, “perfect” double, rather than a more organic one. These are all possible scenarios in which creating artificially double tracked vocals would be appropriate.
When controlled vocal doubling is what you’re after, look no further than Waves Doubler. It allows you to create synthetic vocal doubles by duplicating, panning and adjusting the pitch of your original input signal. Taking it further, Doubler also allows you to apply feedback, modulate pitch at different rates and EQ your duplicated vocals using a low-shelf and high-shelf filter. There’s also a convenient output gain fader that allows you to attenuate the plugin’s output level.
Synthetically creating doubles in this way tends to provide results that are very closely aligned since they tend to lack true, natural randomization. For some genres however, like pop and EDM, this type of effect can work particularly well, as clean, present and wide vocals is what you need. Having said that, the variety of controls that Doubler offers provides it with the versatility of more varied and organic sounding doubles.
Artificial Double Tracking (ADT)
When it comes to creating organic sounding doubled vocals artificially, perhaps for rock, folk or RnB tracks, the artificial double tracking (ADT) method developed by audio engineer Ken Townsend at Abbey Road Studios has long been the industry standard.
In the days of recording to tape, you can imagine how time-consuming recording was in general. The issue back then was that engineers had to spend countless hours double-tracking vocals and hope that the timing of the vocals lined up correctly. Ken Townsend came up with the concept behind artificial double tracking (ADT) and it involved using two different tape machines, which initially included a J37 and a BTR2. A duplicate of the audio signal running through the J37 was also sent to the BTR2, which resulted in a delay time of around 100ms. The result was as close as possible to a genuine double track. This delay could then be modulated to create unique effects.
Waves Reel ADT plugin accurately recreates the sound of artificial double tracking that was initially used at Abbey Road Studios on artists like The Beatles in the 1960s.
The best part about Reel ADT is that you can set the Varispeed LFO rate to random, which achieves the natural variation and randomization found in a real human voice. In general, I find this unit does a great job of recreating an analog tone, which you can further emphasize using the included DRV controls. Another neat feature is that you can create positive as well as negative delay times. You have the choice to push the ADT signal ahead of the SRC signal, which can further open up your creative possibilities. When both signals are centered, you can also create some very interesting slap-back effects that can help push your vocals forward in the mix.
Recording Real Vocal Doubles
The most basic form of recording vocal doubles involves setting up a mic and simply recording your vocalist performing the same part twice. The more skilled your vocalist, the easier this process will be. Ideally, you want them to use the same timing and phrasing they used for the first take to deliver a similar performance. The slight, natural variations in pitch and time are what make this method sound the most “real” out of all the double tracking options on this list, if that’s the vibe you’re going for.
As well, the variations in pitch and time between vocal takes are what allow the aggregate vocal sound to appear rich and full. While it is important to sometimes edit your vocal double takes so the phrasing sits nicely with the lead vocal, if you try to apply too much pitch and time correction you can end up losing the positive qualities that recording doubles will have on your song. Even in the world of pop music where synthetic sounds are coveted, you frequently hear vocal doubles that are slightly detuned.
One thing that should, in general, be treated more heavily when editing the double vocal tracks is the s’s. Sibilant notes tend to have a percussive, harsh attack that can jump out at the ear when repeated in quick succession by more than one voice. This will cause your listener to hear two distinct voices, but in practice, you really only need one “s” from your lead vocal. You can use a quality de-esser plugin like Waves Sibilance or De-Esser to heavily treat the double vocal tracks, allowing them to still sound natural in the mix.
If you’ve brought your vocalist in for a second recording session to track doubles, it’s possible they could be a bit flat or sharp that day. If they’re consistently flat, turning up their headphone mix will cause them to sing with more power, and may be all that’s required for them to hit their notes. If they’re sharp, turn down their headphone mix, and they won’t feel as compelled to compete with the instrumental/lead vocal. You can also use a plugin like Waves Tune to improve the vocal takes after the recording session if you find that adjusting the headphone mix is negatively impacting the vocalist's delivery.
Phase Inverted Vocal Doubles
Phase inverted vocal doubles are going to cancel each other out in mono, but sound incredibly wide in stereo. Over the wailing chorus of engineers screaming in pain as they read this, I’m telling you that, “Yes, complete phase cancelation is ok.” While it’s crucial to take mono compatibility into account, there are many ways you can go about achieving mono compatibility aside from making sure that everything in your song is in phase.
All mono compatibility really means is that your song needs to play back subjectively well in mono; it doesn’t mean that phase cancelation will be the death of your mix. For example, if you have a lead vocal with backup vocals panned out to the sides that will cancel each other out in mono, just add an extra low-level, centered doubled vocal underneath your lead vocal so that there’s a background vocal still present in mono. You now benefit from extremely wide background vocals in stereo while simultaneously looking after mono compatibility.
Creative Ways to Process Vocal Doubles
When trying to separate vocal doubles from a lead vocal, the less similar they sound to the lead vocal the more pronounced they’ll be in the mix. One great technique is to double or harmonize a lead male vocal with a female vocal, or vice versa. You could even use a formant shifting plugin like UltraPitch to create a female-esque voice out of a male vocal. This provides the lead vocal with a unique coloring and thickness.
For rock or heavy hitting hip-hop, you can run doubles through guitar amp plugins like PRS SuperModels. By distorting and saturating your vocal doubles, you’ll add bite and aggressive flavor to overall vocal tone. If you want a more subtle effect, applying heavy compression to your vocal doubles can mellow them out and help them sit nicely beneath your lead vocal.
Songs with sparse arrangements often have space that needs filling; vocal doubles along with spatial effects are a great way to do this. Try setting up a rhythmic delay specifically for your doubles or give them their own reverb, creating a cloud in which to cushion the lead vocal. If your doubles are panned wide, you could also pan the reverb wide. Alternatively, you could mono the reverb for the doubles and stack it behind your lead vocal.
Conclusion
The physics behind doubling vocals may seem somewhat complicated, but physics isn’t what makes great music; it’s your personal taste combined with your skill, so just trust your ears and make decisions that sound good to you.
Experiment with delay times and variations in pitch using plugins like Doubler and Reel ADT, or record vocal doubles yourself. Check your mixes in both stereo and mono and optimize playback as necessary.
When to double track vocals is entirely up to you. You’re now aware that double tracking vocals helps to create width, and one of the most common places to do this is in a song’s chorus. The contrast between a mono vocal in a verse and the filled out stereo field in a chorus is always refreshing. Listen to other songs and see where the artist is using vocal doubles; this is an extremely common effect. You have the tools to create multiple different types of vocal doubles, so try exploring how they can affect your mixes.
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