Double tracking is an effect as old as multitrack recording. As soon as tape machines had advanced to the point where there was a track or two left over after recording the band, someone got the idea that maybe doubling up a vocal might sound cool. And of course it did sound really cool, giving the vocal a depth, width, and timbral richness that could not be achieved with just a single recorded performance. This effect was further enhanced with the advent of stereo recordings, wherein the doubled tracks could be panned left and right in the stereo field for extreme width and separation. Some iconic examples of this effect exist on the recordings of The Beatles, who are responsible for some of the most well known early double-tracked vocal performances, captured primarily during the band's long tenure at Abbey Road Studios in the 1960s.
Double tracking would not long remain an effect strictly for vocals. Guitarists soon cottoned on to the sonic benefits of a doubled performance, and by the 1970s, double-tracked guitars were a standard feature of big rock recordings, as they still are to this day. Any guitar player that has experience recording knows how dramatic the difference can be between a single rhythm guitar track and a doubled one. Doubling is the only way to get that larger-than-life wall of guitars that most rock aficionados of today have come to expect. It's not just for rhythm tracks, though, as metal virtuoso Randy Rhoads proved with the legendary double and even triple-tracked solos that he performed in the studio with Ozzy. This is an incredible achievement, given the speed and technical difficulty of the material, and the precise overdubbing gives these recordings a wholly unique sound.
So big double-tracked tones might be easy enough to pull off in a studio situation, but what about live scenarios where there's only one guitarist? That's really the rub, isn't it? The distinctive sound of a doubled guitar track has everything to do with the subtle differences in timing, pitch, and playing dynamics between two different recorded performances of the same guitar part. It is an effect that is pretty much impossible to perfectly recreate using effects, but many have tried. This is essentially the idea behind slapback and chorus effects, for example, creating the illusion of a second instrument playing along with the first. This is also the idea behind ADT, or Automatic Double Tracking, a tape delay-based effect created by Abbey Road engineer Ken Townsend to save John Lennon (who was particularly fond of double tracking) the trouble of having to record a second identical track of all of his vocals. While no effect can totally nail the sound of real doubling, there are some that come very, very close. Let’s have a look at a handful of the best doubling effects.
Keeley 30ms Automatic Double Tracker
Keeley's entry into the world of double tracking effects is directly inspired by the work of The Beatles and the creative staff engineers at Abbey Road Studios that worked so closely with them. It seeks to replicate these tones, once confined to the recording studio, and bring them to life in a compact stompbox format. I say "mission accomplished," Keeley. The 30ms really recreates the Abbey Road ambience in remarkable fashion, even including an onboard reverb modeled after the studio's distinctive echo chamber. With three different modes of operation, it can function as a very unique modulator, a sweet reverb pedal, a slapback echo, or some combination of these things, but the real draw here is the stereo double tracking effects. The user can tune double tracked voices ±30 cents and tweak delay time from 0–30ms (up to 120ms in Slapback mode). In stereo, the double-tracking is superb and very realistic, especially with a pair of amps spaced some distance apart, or a pair of tracks panned hard right and hard left.
TC Electronic Mimiq Doubler
If you've been yearning to recreate the Randy Rhoads-style triple-tracked solo trick live, then look no further than the brand spankin' new Mimiq Doubler from those mad Danes over at TC Electronic. In fact, you can even one-up our dearly departed Randy, because the Mimiq is capable of creating three distinct new guitar tracks in addition to the original. Laying down four identical rhythm guitar tracks is a pretty common studio strategy on modern metal albums, but attempts to recreate the sound live have mostly fallen flat, until now. From the sound of it, the team at TC has been working very hard to perfect the proprietary new algorithm that makes the Mimiq tick, and I believe they nailed it. The pedal offers control over stereo width, effect level, dry signal blend, and even the precision with which the virtual tracks are doubled, allowing the user to set it for a super-tight, robotic performance or something a little looser and more human. The Mimiq Doubler is a game-changing effect, and once you turn it on you may never turn it off again.
Strymon Deco
The original ADT effects developed by Ken Townsend at Abbey Road were created with tape delays using multiple decks in tandem. Besides the delays, the tape and the machines themselves were a big part of the sound, with their distinctive compression, saturation, and subtle modulation artifacts. The brilliant engineering minds at Strymon tapped into this phenomenon for inspiration and ended up with the Deco, a truly glorious stompbox that recreates the complete tape effects experience on your pedalboard. As with many Strymon pedals the Deco has a mind boggling array of functions, but we are here to discuss the ADT side of things. Deco is capable of spacious and frighteningly realistic stereo double tracking effects enhanced with warm modulation and subtle, random variations that do a bang-up job of mimicking a pair of vintage tape decks running together. Add to this its rich drive, compression, and saturation possibilities, and the Deco becomes like a duo of miniature Studers at your feet.
Electro-Harmonix Polychorus (Double Track setting)
Electro-Harmonix may have been the first company to try and replicate double tracking studio effects in a pedal with its Full Double Tracking Effect (whoever was in charge of naming this one really phoned it in), an under-the-radar vintage unit made around 1979 or so. The FDTE was basically a mono slapback delay with options for 50- or 100-millisecond delay times (which is probably a little too long for realistic ADT effects, actually), and a blend control. This pedal is fairly rare, and probably not worth seeking out unless you're a serious EHX collector, especially since the company has a much more impressive double tracker built into its excellent, highly versatile, and stereo compatible Polychorus. The Polychorus Double Track setting is still basically just a short delay with some chorus, but stereo makes all the difference, and its controls let you really dial in time, width, and detuning.
DIY Double Tracking
Because Automatic Double Tracking is primarily a delay-based effect, it's fairly easy to recreate the sound using pedals you probably already have on your board running into some kind of a stereo setup. It probably won't be quite as impressive as one of the meticulously engineered modern miracles I have listed above, but it'll do, and many pros actually use very similar schemes to simulate double-tracked guitars with their live rigs. First you'll need a delay pedal that can be set for a very short delay time (experiment with settings between 10 and roughly 50 milliseconds) and a single repeat. Ideally you would split your signal between two amps and put the delay, set to 100 wet, in front of one of the amps such that it will receive only the delayed signal. This will get you pretty close to the goal, but adding some kind of detuning or modulation effect like vibrato or subtle flanging on the delayed signal will get you even closer. This setup can really take your places, so experiment and get wild.