Double tracking is one of those things I know I’ll never get tired of. The fact that the simplest of tricks can add so much to a performance has been know ever since double tracking was possible. It’s difficult for us to appreciate just how revolutionary the sound of someone being able to sing along with themselves was when multi track recording first made it possible. The layered harmonies of Mary Ford’s vocals on the records she released with her husband Les Paul back in the 50s still sound striking today!

If tracking something twice is so simple and so effective, why was Automatic Double Tracking invented in the first place? And why do plugins which recreate this effect which was first achieved using a second tape machine and a varispeed control still so popular? At least some of the answer probably lies in the fact that recording doubles is laborious and, depending on the part, sometimes difficult.

How Does Double-Tracking Work?

How to do it couldn’t be simpler, record your part, create a new track and do it again. Play the two parts back and the tiny differences between the two takes create a very attractive thickening effect. The issue here is that those differences have to be tiny. If the double is too loose compared to the original part then the attractive thickening quickly becomes a confusing and amateurish mess!

The important thing here is that the variations are both in pitch and in timing and are irregular. My top tip for getting the best from this technique is not to double-track but to triple-track. If the double is very accurate indeed is it possible for things to start to interfere destructively, not by much but it can still happen. Adding a third part makes this vanishingly unlikely and the third part adds yet more thickness. You might think that adding a fourth or fifth part would make things sound bigger still but my experience is that the opposite can happen, and considering how laborious recording these extra takes can be, the sweet spot for me is triple-tracking.

If Real Doubles Are Best, Why Fake It?

Even if the performer is consistent enough to record really tight doubles, and not everyone is, the decision to double a part can happen during the mix stage, long after the performer has left. In these cases a plugin can be a very acceptable substitute. Here are some choices, from free plugins to offline processes.

If the point of double tracking is to make it sound like there is more than one unison performance then isn’t that what a chorus is designed to do? Well yes, but anyone who has ever tried this will have found that a standard delay modulated with an LFO, which after all is what a chorus is, isn’t very convincing. The deviations are both in time and in pitch but are regular and repeating and the ear soon figures out that it isn’t hearing “real’ double tracking. However not all choruses are the same and if enough delay lines are independently modulated then things improve dramatically. One such effect is Acon Digital’s Multiply

Acon Digital Multiply

This free plugin has been updated from the version in the video, adding an improved EQ but the central features of multiple ‘voices’ which can have their frequency modulation controlled independently from the amplitude make this a distinctly ‘non-swooshy’ chorus which can thicken things in a useful way. While I’m not sure I’d use it on a lead vocal it sounds great on instruments and would sound attractive use tastefully on BVs. And of course it’s free…

iZotope Vocal Doubler

Multiply is an excellent chorus but dedicated ADT plugins are different from chorus, the best of them do more than modulate the pitch and timing with LFOs, they introduce randomness to these characteristics to avoid the ear identifying them as synthetic or fake. How well they achieve this has improved dramatically over time and there is a free option out there for those wanting to try ADT.

iZotope’s Vocal Doubler uses a simple UI to give a convincing double track effect and best of all it’s completely free.

Antares Duo

ADT involves the manipulation of pitch so it’s no surprise that Antares, the inventors of Auto Tune would have a Doubler product. This is a paid for product, costing $69 if you don’t have an Antares subscription but if you have a quaiifying Pro Tools subscription and benefit from the Inner Circle offers Avid make availble to subscribers then you can get Duo for free as part of that offer.

Duo offers manipulation of pitch and timing as well as timbral shifts by manipulating the formant elements of the performance. Hear it in action in the video below.

Sonnox VoxDoubler

In what is a similar product to Antares Duo, in that it is a real time, dedicated ADT plugin which costs a similar amount, VoxDoubler is one of a pair of products in this Toolbox family of products. Thicken and its counterpart Widen illustrate the two uses double tracking are put to.

If the two doubles are panned to the same place in the stereo image, they overlap and thicken each other’s contribution in an attractive way, this is a very common use for this technique on vocals. The alternative use for double tracking is to pan each double to opposing extremes of the panorama to create a dramatic widening effect. Each of these two plugins uses similar processing but to achieve these two related but different effects. Hear Luke using Vox Doubler in the video below.

Synchro Arts Revoice Pro 4 Doubler

Not a standalone plugin but a module found in Revoice Pro 4, this represents the best ADT we’ve heard. While it’s not a real time plugin, is is very easy to use and if you need convincing doubles we’ve not heard anything better. Watch the video below to see William Wittman demonstrate the process and the results.

In conclusion, given the opportunity and a suitably consistent performer we’d always recommend the real thing but if circumstances dictate you need to use ADT there are a range of options out there, from free realtime effects through to premium, offline processes which mean that this most effective of studio tricks is always an option in your project.

How do you do your double tracking?

Photo by Eric Esma