Sound WavesSome instruments, guitars especially, sound great when double-tracked and separated in the stereo image. Hard-panned electric guitars are a standard in modern rock mixes, and engineers have used the technique on acoustic guitars too for decades.

Double-tracking is straightforward: Record a part twice, both takes as similar as possible, and pan one take hard left and the other all the way right. This creates a much wider stereo image than tracking once with a stereo mic, because our ears interpret the separate takes as two different guitars.

All well and good when you decide before recording to use doubled guitars. But what if you realize only after you've started mixing that you need the hard-panned sound, and it's too late to record a doubled track?

You can't simply duplicate the track, and pan one copy left and the other right. That sends the same signal to both channels, so the result is effectively mono. And while it's possible to duplicate the track, and apply effects to one hard-panned copy of it (such as delaying the left side by a few milliseconds,) this yields at best a noticeably fake stereo image. While each channel carries a different signal, our ears quickly sense the similarities, especially in the rhythm and timing.

Here's a trick you can use to get a great stereo effect from mono tracks when the part you'd like to double has repeating sections. With the right source material, this approach yields a result indistinguishable from a properly double-tracked performance.

I'll demonstrate on this guitar riff:

 [download MP3]

The track looks like this in Sonar. Note that it's recorded in mono:
screen shot

The riff has two repeating sections. I've labeled them "part A" and "part B," and each repeats once.

Remember that the stereo effect arises in hard-panned, double-tracked songs because our ears hear two separate guitars playing. Since this track has repeated sections, I can create the illusion of two guitars playing by pairing different repeats of each section. I did that as follows:

  • Duplicate the mono track.
  • Split the second track into its repeating parts.
  • Shuffle the split sections, so that parts A1 and B1 in the first track are paired with parts A2 and B2 in the second, and vice versa.
  • Pan the tracks hard left and right.

screen shot

Now the two tracks each play the same part (A or B) at the same time, but a different "take" of each part. Here's how it sounds:

 [download MP3]

A great stereo spread from a single mono recording!

Note that I left the last section (labeled "part A-3″) the same in both channels so you can clearly hear the difference between the "stereo-ified" version of the track, and the mono that results when both channels play the same thing. And for contrast, I mixed a "fake stereo" version created by duplicating and hard-panning the track, and delaying the left side by 5ms:

 [download MP3]

While this initially sounds like a stereo recording, your ears should quickly sense the overriding similarity in the left and right channels. The stereo effect collapses, especially after repeated listens. Contrast this with the doubled version above which sounds wide and dynamic no matter how many times you hear it!

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