Recording Outside the Box

Jun 14, 2005 6:21 PM, By Pat Kirtley

             

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.

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.