“Virtual Miking” for Acoustic Guitars

Eliminate phase issues when recording acoustic guitar

by Craig Anderton

Using two mics on acoustic guitar is a common recording technique. Although it can give a good stereo image, there may be phase issues due to interaction between the two mics. Stereo miking also requires more setup time.

Recording in mono with a single, high-quality condenser or ribbon mic eliminates phase problems but loses the stereo image. Fortunately, it’s possible to use equalization to create a stereo image from a mono signal. If done correctly, this can result in a spacious, big sound that’s particularly well-suited to solo guitar (especially nylon-string guitar). Furthermore, this lets you dedicate your budget to a single, high-quality mic—you don’t have to compromise on two lesser mics. (With condenser mics, a small-diaphragm type gives the best transient response for a tight, “present” sound; a large-diaphragm mic offers a somewhat “warmer” tone—given only one option, I’d choose the small-diaphragm type.)

CREATING THE VIRTUAL MICS

Start by copying the mono guitar track to two additional tracks. One track will provide the “finger noises/high frequencies” track. Solo it, and set its EQ for a high-pass filter response with a 24dB/octave slope and frequency around 1kHz. Pan this track right; after all, if you’re facing a guitarist the finger and fretting noises will be to the listener’s right (Fig. 1).

Fig. 1: The three audio tracks are to the left, with the original at the top. The EQ to the immediate right shows the 24dB/octave lowpass filter response, while the EQ to the far right shows the 24dB/octave highpass filter response (unused EQ sections are grayed out for clarity). The Gloss button is a Sonar X-series feature that adds a little extra “sheen” to the highs.

The second copied track is the “guitar body” track. Solo it and set its EQ response to lowpass, again with the slope to 24dB/octave, and frequency to about 400Hz. Pan this track left, as it emulates the guitar body’s “boom.”

While monitoring all three tracks, pan the original track to center and bring up its level. The result should be a big, stereo guitar sound—but we’re not done yet.

THE VIRTUAL COMBINATION LOCK

Think of this technique as a combination lock, where everything has to line up just right for the lock to open. The level balance of the three tracks is crucial, as are the EQ frequencies. Experiment with the EQ settings, and consider trimming the ranges covered by the high and low tracks in the original track. For example, if the “body” track consists mostly of frequencies below 400Hz, trim frequencies below 400Hz from the original track to increase the separation. You might also want to trim the original track’s highs in the same range as the finger noises track. Then again if the image is too wide, pan the two copied tracks more to center.

You may be pleasantly surprised to hear a stereo guitar with no phase issues—the sound is stronger, more consistent, and the stereo image is rock-solid. Give it a try next time you need to mic an acoustic guitar.

Craig Anderton is Editor Emeritus of Harmony Central. He has played on, mixed, or produced over 20 major label releases (as well as mastered over a hundred tracks for various musicians), and written over a thousand articles for magazines like Guitar Player, Keyboard, Sound on Sound (UK), and Sound + Recording (Germany). He has also lectured on technology and the arts in 38 states, 10 countries, and three languages.