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electronic MUSICIAN

Recording Outside the Box

By Pat Kirtley | March 1, 2004

In the early 1930s, before the word “transducer” was ever heard, a 13-year-old named Lester Polfuss jammed the needle of a phonograph cartridge into the wooden top of his guitar in a desperate attempt to electrify it on the cheap. It wasn't the first means anyone had discovered to amplify or record the sound of a guitar, nor would it be the last, but it was a quirky alternative to the established ways. It did the job, and the kid who grew up to be Les Paul was using his creative mind to think outside the box.

For electric guitar, we've long accepted that tone is produced not just by the instrument, but by amps, speakers, and any number of electronic modifiers. But the conventional thinking about acoustic-guitar tone remains nailed in place by a purist viewpoint that says that all tonal flavor should come from the characteristics of the instrument itself and the hands of the player. Freed from this rigid thinking, acoustics can probe the same flexible tonal boundaries as electrics while still preserving their innate qualities. A fearless acoustic attitude is displayed by adventurous players such as Lindsey Buckingham, Steve Morse, and Adrian Legg, who record acoustic tone in uncommon ways.

The sizable body of literature about methods for recording acoustic guitar prescribes mic types, patterns, angles, and distances, which together constitute an industry standard for getting a balanced sound. However, by throwing off the constraints of accepted practice and using aggressively unorthodox techniques, you can create unique textures; get a lush, fat tone; and work around nasty audio problems. The following ideas have worked for others and may be helpful to you too.

NONTRADITIONAL MICS

Most reference books recommend starting the quest for acoustic-guitar nirvana with a pair of small-capsule condenser mics. It's a tried-and-true formula, and with a good room and proper placement it yields predictable results.

Small-diaphragm condensers have a signature sound characterized by silky extended highs and natural extended lows — the perfect mic, you might think. But sometimes the extended range emphasizes certain sounds that would be best left out: the scratchiness of pick attack; string squeaks on the high end; and annoying, nonmusical rumbles on the low end. You can roll off the EQ, but a glovelike fit sometimes comes in the form of the garden-variety dynamic mic. Preconceived notions aside, most engineers are aware that many good recordings of acoustic guitar, especially in live-stage setups, are made with the ubiquitous Shure SM57 or similar mics.

The everyday cardioid dynamic doesn't have extended high-frequency response past 15 kHz or so, and it won't catch those 20 Hz lows the way that many condensers will. That can be a good thing, because the low end of a guitar doesn't go that far down anyway. The fundamental of the low E string is about 80 Hz. Dynamic mics have another benefit that fits the character of lightly played acoustic guitar sounds: a noise floor that's typically lower than those of all but the most expensive condensers.

FIG. 1: A pair of lavaliere condenser microphones attached to the guitar's body with double-sided tape can provide surprisingly good results.

If small-capsule condensers work well, what about really small condensers — the ones the size of a pinky fingertip, which are typically used as lavalieres for voice pickup. Some of those mics are very good, and their size lets you place them in unconventional positions. For years, guitar manufacturers and technicians have been installing these insect-size condensers inside of guitars, but the results are often disappointing. Why? One reason is that inside the box there are a huge number of standing-wave nodes — resonances that work together to vibrate the guitar's wooden surfaces but that, when picked up at almost any fixed location inside the chamber, sound quirky and unbalanced. Putting mics inside the guitar, especially for recording, is too problematic.

I like to use a stereo pair of minimics on the outside of the guitar, in a place that looks weird but sounds great. I put them on either side of the fretboard right against the body, temporarily held in place with double-sided tape. The tape helps to secure the mic and also isolates the mic body from direct vibrations of the wood. Another method that yields similar results is to clip the two minimics to the edges of the sound hole with felt padding under the clips for shock isolation (see Fig. 1). Listen to lots of mics on acoustic guitar — don't fear any of them.

BASIC BLENDS

You can get effective guitar tones by combining standard mic configurations with the output of an onboard guitar pickup. For steel-string acoustics, use the classic condenser-mic pair augmented by a magnetic pickup placed in the sound hole. For years I kept a Bill Lawrence snap-in magnetic in a studio drawer just for that purpose. Most engineers and musicians consider such a pickup by itself unsuitable for recording — it has that characteristic electric-sounding one-dimensional tone that you love to hate in an acoustic. But consider its good qualities, such as rock-solid bass response and extra sustain.

FIG. 2: Using a pair of condensers in conjunction with a magnetic pickup can give you a big sound. At mixdown, try panning the condensers right and left and putting the magnetic pickup's output up the middle.

Typically, you record the stereo mic pair on two tracks and the pickup on its own third track. During mixdown, you can refine the blend in a number of ways. One is to EQ away the upper mids and highs from the pickup and remove the bass frequencies from the mic pair at the same time, giving you the microphone equivalent of a two-way crossover. A typical panning scheme is mics full left and right, and pickup centered (see Fig. 2). The result? A “bigger than life” acoustic sound that's perfect for situations in which the guitar is prominent in the mix (see Web Clip 1). In this scenario, I generally use about 75 percent mic sound and 25 percent pickup sound. A useful bonus is that the onboard pickup is relatively isolated from outside acoustic sounds. If low-frequency rumble in the ambient environment is a problem, such a setup is part of the cure.

Standing this notion on its head, wonderfully spacious sounds materialize when you mic the body of an electric guitar. Even solidbody electrics radiate considerable high-frequency acoustic energy directly from their bodies — airy tones that are entirely lost through the guitar's normal pickups. Hollowbody archtops have an even bigger acoustic tone. The trick is to mic the guitar as if it were an acoustic, and then blend the mic sound with the usual mic-in-front-of-amp tone. No matter the type of guitar or the playing style being recorded, this idea is worth trying in your quest for capturing unique guitar sounds. It's amazingly easy, and there are no critical parameters — simply stick the mic out there and find a blend. Usually, just a little of this acoustic sound will add clarity and dimension.

STRANGE PAIRS

You can pay big bucks for a laboratory-matched pair of microphones, complete with paperwork to confirm their common source of electrical DNA. It's a starting point for many classic techniques for recording acoustic guitars. The idea is to create a spacious, balanced stereo field. That's great for audiophile recordings of solo guitar, but a technique that offers far more possibilities is to use two completely different mics. For instance, try putting a small-cap condenser up by the neck and a dynamic down by the lower body. When the tracks are panned fully left and right, the stereo perspective is greatly exaggerated, and sometimes that is exactly what you want (see Web Clip 2).

I once got a luscious, fat sound with an AKG C 451 B on one side and a Shure ES615 omni “room-equalization” mic on the other. Similarly interesting results can be had with a large-diaphragm tube mic on one side and a dynamic cardioid “stage mic” on the other. A caveat: pay attention to potential phasing problems between extremely dissimilar mic pairs.

OMNI IS BEAUTIFUL

Directional microphones were developed for good reasons, the main one being focus, or the directional admittance of desired sounds and rejection of unwanted ones. Most of the microphones used in studio work are directional types — cardioid, supercardioid, or bidirectional (figure-8). The ability to reject unwanted sound comes at a cost, and one of the liabilities is the proximity effect: whenever a directional mic is placed close to the source, bass frequencies are overemphasized. That can be a significant problem when recording acoustic guitar, especially if you want to position a mic anywhere near the sound hole.

Omnidirectional mics are totally free of this bass-boosting aberration, and when you can use them, the open, airy quality can be striking. Most people don't think of omni mics when recording acoustic guitars because they pick up more reflected room sounds than the directional types do. However, since they are free of proximity bass-boost, you can place them closer to the instrument and maintain a good balance between guitar and room (see Web Clip 3).

MONO, ANYONE?

It's a habit to deploy a stereo mic pair to record acoustic guitar. But the stereo concept itself, as exemplified by a left-right speaker pair, is overrated in my opinion. At no time does the recordist have any control over the listener's speaker setup, which may be anything from an audiophile listening system to a cheap boom box to headphones. A stereo image that sounds crisp and spacious in the control room is sometimes blurred at end-user playback.

Summing a stereo pair to mono, especially with acoustic guitar as the subject material, can bring potential foibles to light. But there's a technique that often reveals sonic truth for all to experience: just use one mic. Doing so can be tricky, because it forces the recordist to find the precise distance and angle that will yield the best balance. But once the spot is found, a single-mic perspective can give a track a satisfying “already mixed” quality.

If you're afraid to commit, try this compromise: record a stereo pair of tracks as usual, but add a third (mono) mic on its own track and compare the two versions. You might be converted to this underused method. If you need more convincing, listen to some late '50s to early '60s, one-mic, classical guitar recordings made before stereo was popular. Do you have only one high-quality condenser tube mic that you usually reserve for recording vocals? Try it on guitar.

GIVE AMPS A CHANCE

Recording directly from an acoustic guitar's built-in undersaddle pickup system rarely yields pleasant results. The sound tends to be strident and one-dimensional. Taking a cue from the late, legendary guitar master Chet Atkins, consider plugging into a guitar amp and miking it.

What might seem like the ultimate heresy to the purist camp was Atkins's preferred method when he recorded his acoustic-electric nylon guitars. And he didn't use one of those new-fangled clinically accurate “acoustic” amps either — his choice was more likely a tube amp made for electrics, typically his vintage Standel with a single 15-inch speaker. His mic of choice was either a Neumann U 87 or an old RCA 44DX ribbon.

MIDI BLENDS

Synthesis and MIDI are basic components of keyboard setups, but they are not as commonly associated with guitar, especially acoustic guitar. Indeed, many people would consider the electronic tones of a synthesizer to be the antithesis of the pure, organic sound of an acoustic. I've found, however, that you can create lots of cool new tonal possibilities by using the synthesizer's tonal palette to embellish that of the guitar when recording.

A simple way to bring synth capabilities to your acoustic guitar is to equip it with a synth pickup. For example, you can mount a Roland GK-2A (temporarily) on your guitar, enabling your instrument to drive a compatible synth and giving you the means to record simultaneous synthesizer and acoustic guitar parts.

FIG. 3: The method shown here involves miking an acoustic guitar that's equipped with a synth pickup. The pickup drives a synth module whose output is routed separately to the multitrack, where it serves as an ethereal "ghost" track to supplement the main guitar sound in the mix.

A particularly effective approach is to set up the synth with a string patch or slow-attack sample that “follows” the guitar with orchestral lushness (see Fig. 3 and Web Clip 4). Depending on how the mix is done, it can be a subtle background that blends into the reverb, or a thick sound that stands independent from the guitar tone, as if a keyboardist were playing along. Another cool trick is to feed the synth pad to the reverb send during the mix, but mute the direct sound of the synth track. The resulting reverb effect (which the ear interprets as originating from the guitar) can range from airy to otherworldly.

Many recording setups, computer based or otherwise, allow you to record MIDI data in sync with the audio tracks (if you're using the GK-2A, you'll need to plug into a GK-compatible synth or interface in order to get a MIDI out). By recording the MIDI data generated by the guitar synth, you create a trigger track that can drive synths in a number of ways during mixdown, widening the spectrum of possible tonalities and choices immensely.

SLICK TRICKS OF THE STARS

You needn't limit yourself to mic or electronic techniques when going for boldly different guitar sounds. A staple trick for years in country music has been to set up a guitar with the “Nashville Tuning,” which involves raising the pitch of the lower four strings an octave by using individual strings from a set for 12-string guitar. The octave shift creates a sound with lots of stringy harmonics but no lows or low mids to muddy the mix.

Another trick invented in Music City is much less known. This one came from Chet Atkins (and was also used by Jerry Reed) in the days before digital effects units existed. Atkins recorded a track and then slightly detuned all the strings of the guitar and played identically on another track. The result is something like chorusing, but with its own unique character, and nothing about it sounds digital. By varying the amount of detuning (chromatic digital tuners make it easy to get an exact detuning), you can go from subtle and spacious to something pretty crazy. It works well for guitar solo parts too. The hardest part is playing exactly the same way twice in a row (never any trouble for Atkins and Reed).

BE RECKLESS

While there are few guitar recording challenges as exciting as the ones faced in the early days, the ideas in this column are guaranteed to add refreshing colors to lifeless guitar sounds. I know: I've had occasion to try them all, usually out of blind desperation. (“Must get killer guitar sound!”) My reckless extremes were never as deeply driven as the young Les Paul's, but my desire for a unique sound is just as serious.

If nothing else, using these techniques will change your attitude about recording acoustic guitar and help avoid the same-old-same-old syndrome on your next recording. By all means, read the textbooks about recording acoustic guitar and learn the classic techniques, but next time you pull out the six-string, feel free to go a little nuts.

Pat Kirtley is a guitarist, composer, and recording artist with an extensive background in pro audio. His latest CD release is Brazilian Guitar (MainString Music, 2002).

ACOUSTIC ALTERNATIVES

The various nonstandard methods for recording acoustic guitar discussed in this article are summarized below.


METHOD MIC/TRANSDUCER ADVANTAGES
Dynamic Mics Cardioid dynamic mic pair Narrower frequency range of dynamic mics means they pick up fewer scratches and squeaks in the high end and less rumble in the low end.
Guitar and Synth Acoustic guitar with MIDI pickup, sound module, mic Blend of straight acoustic sound with MIDI “ghost track” yields interesting tonalities.
Lavalieres Attached Stereo pair of mini (lavaliere) condensers attached to neck or sound-hole edges Mics move with the guitar so player movement isn't restricted. Bass- and treble-side perspectives are both picked up.
Mic the Transducer Piezo transducer on guitar, dynamic or condenser mic for amp Miked amp sound is often better than the pickup's direct sound.
Mismatched Mics Two different mic types Exaggerated stereo perspective.
Mono Miking One high-quality condenser Can sound good if correctly placed. Blends in track well.
Nashville Tuning (four lowest strings replaced and tuned an octave up) Condenser (or dynamic) mic(s) Lots of rich harmonics, no low-end muddiness.
Natural Chorusing (two detuned guitars overdubbed playing the exact same part) Condenser (or dynamic) mic Organic-sounding chorusing, varied by amount of detuning.
Omni Miking Omni mic pair or single omni mic Lets you position mic closer to sound hole without causing proximity effect. Good blend of direct and room sound. Natural tonal balance.
Pickup Blended In Stereo pair of condensers, magnetic pickup Big sound with miked signals panned left and right and pickup sound up the middle.
Pickup Through Amp Pickup-equipped acoustic guitar, amp, mic for amp Fattens and smooths tone, especially for acoustic-electric guitars.

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