by Craig Anderton
Although the goal with acoustic guitar is often to create the most realistic, organic sound possible, a little electric-type processing can enhance an acoustic’s sound in many ways that open up new creative avenues. We’ll assume your acoustic has been electrified (presumably with a piezo pickup) and can produce a signal of sufficient level, and of the proper impedance, to drive contemporary effects units. If you're not sure about this, contact the manufacturer of the pickup assembly, or whoever did the installation.
There are quite a few processors dedicated to acoustic guitar, like Zoom’s A3 (Fig. 1).
Fig. 1: Zoom’s A3 packages acoustic guitar emulations and effects in a floor pedal format.
While convenient and cost-effective, but this article takes more of an à la carte approach with conventional, individual effects.
Most electrified acoustics have frequency response anomalies—peaky midrange, boomy bass, and so on—caused primarily by the interaction among the guitar body, pickup, and strings. While some of these anomalies are desirable (classical guitars wouldn't sound as full without the bass resonance most instruments exhibit), some are unwanted. Smoothing out the response is a task for equalization.
There are two main types of equalizers (EQ for short) used with acoustic guitar, graphic and parametric. A graphic EQ splits the audio spectrum into numerous frequency bands (Fig. 2).
Fig. 2: Source Audio’s Programmable EQ is a graphic EQ that can save and recall custom settings.
Depending on the model, the range of frequencies (bandwidth) covered by each band can be as wide as an octave to as narrow as 1/3 octave. The latter types are more expensive because of the extra resolution. The response of each band can be boosted to accent the frequency range covered by that band, or attenuated to make a frequency range less prominent. Graphic equalizers are excellent for general tone-shaping applications such as making the sound "brighter" (more treble), "warmer" (more lower midrange), "fuller" (more bass), etc.
A parametric equalizer has fewer bands—typically two to four—but offers more precision since you can dial in a specific frequency and bandwidth for each band, as well as boost or cut the response. So, if your guitar is boomy at a particular frequency, you can reduce the response at that specific frequency only and set a narrow bandwidth to avoid altering the rest of the sound. Or, you can set a wider bandwidth if you want to affect more of the sound.
Either type of equalization can help balance your guitar with the rest of the instruments in a band. For example, both the guitar and the male voice tend to fall into the midrange area, which means that they compete to a certain extent. Reducing the guitar's midrange response will leave more "space" for your voice. Another example: if your band has a bass player, you might want to trim back on the bass to avoid a cluttered low end. However, if your band is bassless, then try boosting the low end to help fill out the bottom a bit.
Note that piezo pickups have response anomalies, and equalization is very helpful for evening out the response. For more information, check out the article “Make Acoustic Guitar Piezo Pickups Sound Great” at Gibson.com.
BRIGHTNESS OR FULLNESS WITHOUT EQUALIZATION
Many multieffects offer pitch transposition. I've found that transposing an acoustic guitar sound up an octave (for a brighter sound) or down an octave (for a fuller sound) can sound pretty good, providing that you mix the transposed signal way in the background of the straight sound—you don't want to overwhelm the straight sound, particularly since the processed sound will generally sound artificial anyway.
A delay line can simulate having another guitarist mimicking your part to create a bigger-than-life, ensemble sound. Run your guitar through a delay set for a short delay (30 to 50 milliseconds). Turn the feedback (or regeneration) and modulation controls to minimum; this produces a slapback echo effect, giving a tight doubling effect.
Another option is chorusing, which creates more of a swirling, animated sound as opposed to a straight doubling. The settings are similar to slapback, except use a shorter delay (around 10 to 30 milliseconds) and add a little modulation to vary the delay time and produce the "swirling" effect. Note: with most delay effects, it's best to set the balance (mix) control so that the delayed sound is less prominent than the dry sound.
Guitars are percussive instruments that produce a huge burst of energy when you first pluck a string, but then rapidly decays to a much lower level. Often this is what you want, but in some cases the decay occurs too quickly and you might prefer more sustain.
A limiter is just the ticket. This device decreases the guitar's dynamic range by holding the peaks to a preset level called a threshold, then optionally amplifying the limited signal to bring the peaks back up to their original level (Fig. 3).
Fig. 3: The signal with 4dB limiting (blue) has a higher average level than the original recording.
Don't set the threshold too low, or the guitar will sound "squeezed" and unnatural. Also, although many people confuse limiters and compressors, these are not identical devices. A compressor tries to maintain a constant output in the face of varying input signals, which means that not only are high-level signals attenuated, but low-level signals may be subject to a lot of amplification.
The above explanation of limiting is fairly basic, and there are several variations on this particular theme. Early model limiters would simply clamp the signal to the threshold; newer models can do that, but may also allow for a gentler limiting action to provide a more natural sound.
PEDALLING YOUR WAY TO BIGGER SOUNDS
If you have a two-channel amp or mixer, one trick that's applicable to all of the above options is to split your guitar signal into two paths with one split carrying the straight guitar sound, while the other goes through a volume pedal before feeding the desired signal processor. Use the volume pedal to go from a normal to processed acoustic guitar sound, and bring in as much of the processed sound as you want.
The possibilities for processing acoustic guitar are just as exciting as for processing electric guitars. The best way to learn, though, is not just by reading this article—my intention is to get you inspired enough to experiment. You never know what sounds you'll discover as you plug your guitar output into various device inputs.
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.