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Tracking in Small Studios

July 1, 2014
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Essential tips for instrument, amp, and mic placements

At the start of a recording session, many engineers position musicians and their equipment based solely on ergonomics before placing mics. That might do in a large tracking room, but in a small space—where suboptimal acoustics can make a damaging imprint on the sound—it can lead to flawed recordings that are impossible to fix at mixdown. Here are some essential points you should consider when setting up musicians, gear, and mics in a small studio.

 
Fig. 1. The spectragraph in Metric Halo SpectraFoo Complete shows deep notches in frequency response at 73 and 128Hz, due to room modes occurring at a specific spot in a studio. The horizontal axis delineates frequency (limited here to the bass band), while the vertical axis denotes amplitude. The severity of these notches is typical for a small room.
Optimize the Source
In a small room, the position of the sound source you intend to record (for example, an amp) can have a far more dramatic effect on sound quality than mic selection. Room modes—severe notches and extremely narrow peaks in the room’s frequency response—can wreak havoc on an ill-positioned amplifier or instrument’s bass reproduction. These powerful and immutable variances in sound pressure at specific frequencies—most problematic in the bass band—exist at specific locations throughout every studio but exert the greatest influence in small rooms (see Figure 1). The frequencies at which they occur vary according to room proportions.

If your source sounds thin or boomy, try moving it one foot forward or backward, or left or right, and see if that improves the sound. Moving an object only one foot on an axial plane to walls can remove it from the powerful influence of a room mode.

You can determine where room modes occur in your studio by playing back bass-heavy music on full-bandwidth speakers while walking the room. Wherever you hear a peak or dip in the reproduction of an isolated bass note, that’s where a room mode exists. And that’s also where you should avoid setting up that’s also where you should avoid setting up instruments, amps, and mics to record.

Establish Boundaries If a bass amp, for example, needs more bottom end overall, move it closer to a wall. Doing so will boost its reproduction of bass frequencies, courtesy of what’s known as the boundary effect. A room’s corner will boost overall bass response even more, but don’t put the amp there—room modes terminate in corners in their travel, so placing anything in a corner is a recipe for uneven bass response.

You can decrease excess bottom end from an acoustic guitar, for example, by moving the performer farther away from a wall (making sure you don’t place them where a room mode exists farther out into the room). You can make a guitar amp sound less bassy by moving it off the floor (which also produces a boundary effect) and onto a sturdy chair; doing so will yield a far better recording of the guitar than if you had messed with the amp’s tone controls to fix the imbalance. (The filters’ bandwidths and slopes are highly unlikely to provide an exactly inverse effect to the boundary effect exerted by the floor.)

Avoid Glass and Diffusors Try not to place your sound source near an observation window; sound reflecting off the glass will cause comb filtering at the mic. (Comb filtering involves nasty phase cancellations that hollow out the sound and are impossible to fix at mixdown.) And while acoustic diffusors are excellent acoustic solutions to liven a dead room and prevent slapback echoes off of hard walls, you should avoid miking up a sound source within six feet of them to avoid a phase-y sound.

Lend an Ear Now that your sound source is positioned in the studio for the best sound possible, it’s time to position your mic. In order to avoid capturing a horribly uneven bottom end, you’ll want to place the mic where a room mode doesn’t occur. Aim one of your ears at the sound source and move your head around: left and right, up and down, and closer and farther away from the sound source. Listen to how the sound changes, and note the spot where it’s the best. That’s where you should place your mic.

There will often be two great-sounding spots to mike up a large instrument or amp cabinet, and the different attributes accentuated by each spot (for example, the resonating body of the instrument and the pluck of a string) may strongly suggest using two mics to capture the composite sound. If you want to make a stereo recording using a spaced pair of mics, try to position the two mics so that the distance between them is at least three times the distance of each mic to its sound source. Observing this general rule will minimize phase cancellations in the stereo recording, but it may mandate that you place the mics very closely to the sound source. If practical considerations decide you can’t follow the 3-to-1 rule, consider using a coincident or near-coincident pair of mics—placed at the position your ear determined sounded the best—to record the instrument in stereo.

Selecting the most flattering mics and their configuration (such as a coincident pair) is an important part of recording, but it should never be your starting point. The best mic in the world can’t correct a room mode or comb filtering. Get the sound right at the source, and you will make great recordings. All the rest is secondary.

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