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Cabinet Miking
Guitar Miking: Getting a Great Guitar Sound
by Barry Rudolph
Part 1: Intro / Mic Choices / Shure SM57 / Sennheiser MD421U
What makes a great guitar recording? Start with a good player, the right amp, and a sweet sounding axe. Engineers can work magic with less, but it's unrealistic to expect a great track from a lame sounding amp, guitar, or performance. But let's assume that the goods are coming from the speakers. To get that magic on tape (or disk), the recording engineer must combine his knowledge of guitars and amplifiers with an understanding of microphones and miking techniques. The ideal sound is the one that best fits the guitar part, the song, and the genre of production. While there are many excellent options for direct recording available today, we're interested here in the time-honored tradition of miking up amplifiers.
Choosing and positioning microphones are crucial steps in shaping and capturing a guitar sound. The wrong mic, or even the right mic in the wrong place, can sabotage even the best sounding amp. Conversely, you can use mic placement to enhance the best qualities of an amp's sound. And while there are no hard and fast rules -- you'll need to use your ears to decide what's working -- we can tell you where to begin.
Choosing a Microphone
Microphone choice is as big a part of the guitar sound as any other factor: Mic type will greatly influence the player's tone and, by extension, the performance. There are almost as many mics and setups to choose from as there are amps and guitars. Let's take a look at some favorites.
The Trusty Shure SM57
The Shure SM57 cardioid dynamic is the most common microphone used to record electric guitar. This started back when all the more expensive microphones had already been used in big tracking sessions. Engineers were left with the lowly Shure to handle those loud, cranky, noisy guitar amps. Fortunately, it turned out that the SM57 was perfect for the task; its frequency response, originally tailored for speaking, matches the mid-range "voice" qualities of the guitar. The SM57 also has a compression effect on loud sounds; it squashes nicely, facilitating the engineer's job of maintaining consistent recording levels.
You'll see engineers push a SM57 right into the grill cloth of an amp cabinet, taking advantage of the proximity effect, which boosts low frequencies when the mic is placed close to a sound source. The SM57 locks in a certain "size" for the electric guitar, maintaining its appropriate place in the mix without additional EQ or compression.
Sennheiser's MD421U
The Sennheiser MD421U cardioid dynamic is also popular. It offers a wider frequency response (more high and low frequencies) than the SM57. A five-position rotary switch adjusts the frequency response from the flat position, called M (for music), all the way to the contoured S (for speech). Generally, I find the 421 brighter with less of the compression effect than the SM57. These mics are also more directional than the Shure, which is important for isolating the sound coming from one speaker in a multi-speaker cabinet.
Part 2: Condensers / Royer R-121 Ribbon
Condenser Microphones
Dynamic mics may be the most common choice for electric guitar recording, but condensers also work great. Just be careful not to get an overly bright sound. I often place a condenser mic further away from the speakers to capture a cabinet sound.
Figure 1 shows a Shure KSM44 condenser about 20" from a 1960's-vintage Marshall 4x10 cab. (I was auditioning the three cabinets in the picture.) With this setup, the guitarist might complain that his amp sounds brighter than usual, especially compared to a SM57, and feel he must readjust his amp's settings.
Condensers also pick up more low frequencies from the amp than dynamic mics. This may or may not be a good thing; pushing a lot of air might work in a heavy metal track, but can be inappropriate for a lighter pop song. Certain condensers can overload when close-miking extremely loud amps. Occasionally, the mic's metal windscreen can get loose and vibrate. Always use the attenuator pad and, if necessary, the low frequency roll-off. The Neumann U-87 and U-47FET, Shure KSM44 or the Audio-Technica AT-4041 are all good choices.
Many condenser mics also offer an opportunity to experiment with different polar patterns, such as omni-directional and figure-8. Omni mics differ from cardioids in that they do not exhibit proximity effect. Omnis, which receive signal from all around the capsule, pick up more of the total sound of the amp and room tone (as opposed to the cardioid sound, which focuses on the source in front of it). This makes the omni pattern a good choice for ambient guitar sounds and, when used in a multi-mic setup, as room mics. Figure-of-Eight mics also pick up more of the room than cardioid mics, receiving signal at the front and back of the capsule.
Royer R-121 Ribbon Microphone
Speaking of figure-8 mics, my new favorite for guitar is the ribbon microphone. I have a pair of Royer R-121 figure-8 microphones that offer a whole new range of warm electric guitar sounds. Big, cumbersome ribbon mics have been around for years, but these fragile units were notoriously prone to damage when used on loud instruments. The lighter and smaller Royers can handle huge volumes without the worry.
Like other figure-8 mics, the Royer picks up sound from two opposing sides in what is also called a bi-directional pattern, and you can take advantage of this to get more of the recording space or room in the sound. (Experts note: The sound entering the rear of the mic is 180 degrees out-of-phase with that coming into the front.)
When A/B'ing the Royer against the SM57, one engineer remarked to me, "When you switch from the Royer back to the 57, you wonder where half the guitar sound went." While a big, fat, and warm guitar sound like the one described here might sound ideal on its own, make sure it fits your mix before you commit to it.
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