AudioRamblings

4th February 2010

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Numerous attempts have been made to find a process that can be applied to a single vocal part to make it sound double-tracked. Some have proved reasonably successful, and others that failed on a technical level have become effects in their own right.
The Real Fake: The first, and most obvious, process was ADT, or automatic double-tracking, which was usually accomplished by using the playback-head monitor facility of a tape recorder to produce a short ‘slap-back’ delay. It’s this technique that creates the familiar effect that was used on countless early rock & roll records, and was famously exploited by artists such as John Lennon.
You can create the ADT effect easily using modern technology. Simply add a digital delay to the vocal at around the same level as the original part, with a delay time of 80-120ms, and then turn the feedback control to minimum so that you get only one repeat.
Pitch Modulation: More sophisticated emulations combine slight time-delays with pitch modulation or pitch offsetting. One of the earliest devices to do this, the Drawmer Double Tracker, was based on analogue charge-coupled delay-line chips, plus an LFO for gentle pitch modulation. The Double Tracker is no longer in production, but you can get similar results by applying a very shallow, slow pitch-modulation to your digital delay line, to imitate the natural pitch variation that occurs with double-tracking. You could also roll some top end off the delay to mimic the limited bandwidth of those analogue delay chips. Plug-ins such as PSP Audioware’s Lexicon PSP42, which includes a ‘Doubler’ preset, can give a similar effect.
Pitch-shifting: An alternative to pitch modulation is to use pitch-shifting, just as we did earlier with real double-tracked parts. Move the original up by four to eight cents, and the delay down by the same amount. This approximates the kind of pitch difference that might occur in a real performance and avoids the sometimes obvious cycling effect of LFO-driven modulation.
Emulating Real Double-tracking: We now have software plug-ins such as Antares Duo that try to get closer to a genuine double-tracking effect, something that’s achieved by making the small timing and pitch discrepancies between the original and delayed parts more random. Some also create not just a second vocal line but several parts, and allow the formant of the voice to be shifted slightly to create a different character for each of the added parts.
PSP Audioware’s Lexicon PSP42 can be used to create very short, bright modulated delays, that give a rich, textured effect similar to ‘authentic’ ADT.
PSP Audioware’s Lexicon PSP42 can be used to create very short, bright modulated delays, that give a rich, textured effect similar to ‘authentic’ ADT.
If you have a DAW and a basic set of plug-ins, you should be able to combine them to find your own recipe for fake double-tracking. Here are some strategies you can try.
First, copy your vocal onto a second track, delay it by 80ms or so, then use a pitch-correction plug-in to pull it tightly into pitch, but not so tightly that it sounds false or robotic. Even if the original part was very well sung, there should now be enough pitch difference to create an audible effect. If you go too far you can end up with a phasey character, in which case use a slower rate of pitch-correction. It’s worth pointing out that though this phasey effect is normally unwanted, it can be great as a special effect in its own right and can be great on guitar.
A variation on this theme is to use a program that lets you change the depth of vibrato present in the original performance without changing the nominal pitch. Some DAWs, such as Cubase 5, have this functionality built in, but if yours doesn’t, you can use a third-party processor such as Melodyne. By reducing or increasing the vibrato depth of the second part (which should ideally still be delayed slightly) you may get enough variation to create the desired effect.
For a more subtle ADT effect, try using a reverb program that allows you to create only early reflections (or a short ambience) instead of traditional delay — something like Smartelectronix Ambience is ideal. What you’re aiming for is a short burst of fairly bright reflections with no reverb tail. If you bring the pre-delay value up to 80ms or thereabouts, you’ll hear a rich ADT effect that’s less mechanical-sounding, with fewer phasey artifacts than pure delay. You can still combine this with any of the pitch-shifting or modulation techniques already discussed, and feeding the reverb via a pitch-correction plug-in can often be successful.

Tagged: vocalsMixingeffects