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Microphone Technique Basics For Musical Instruments

The cause and effect of microphone placement and techniques with instruments in recording sessions...

By Bruce Bartlett May 28, 2015

Photo courtesy of SD Systems.

Suppose you’re going to mike a singer, a sax, or a guitar. Which mic should you choose? Where should you place it?

Your mic technique has a powerful effect on the sound of your recordings. In this article we’ll look at some general principles of miking that apply to all instruments.

Which Mic Should I Use?
Is there a “right” mic to use on a piano, a kick drum, or a guitar amp? No. Every microphone sounds different, and you choose the one that gives you the sound you want. Still, it helps to know about two main characteristics of mics that affect the sound: frequency response and polar pattern.

The frequency response of a mic is the range of frequencies it can pick up at an equal level (within a tolerance, such as +/- 3 dB). Most condenser mics have an extended high-frequency response—they reproduce sounds up to 15 or 20 kHz. This makes them great for cymbals or other instruments that need a detailed sound, such as acoustic guitar, strings, piano, and voice.

Dynamic moving-coil microphones have a response good enough for drums, guitar amps, horns, and woodwinds. Loud drums and guitar amps sound dull if recorded with a flat-response mic; a mic with a presence peak (a boost around 5 kHz) gives more edge or punch.

Suppose you’re choosing a microphone for a particular instrument. In general, the frequency response of the mic should cover at least the frequencies produced by that instrument. For example, an acoustic guitar produces fundamental frequencies from 82 Hz to about 1 kHz, and produces harmonics from about 1 to 15 kHz. So a mic used on an acoustic guitar should have a frequency response of at least 82 Hz to 15 kHz if you want to record the guitar accurately.

Here are the frequency ranges of some instruments (including fundamentals and harmonics):

Male voice: 100 Hz to 12 kHz
Female voice: 200 Hz to 12 kHz
Kick drum and bass: 40 Hz to 9 kHz
Guitar through an amp: 82 Hz to 4 kHz
Acoustic guitar: 82 Hz to 15 kHz
Cymbals: 500 Hz to 20 kHz
Toms and snare drum: 100 Hz to 12 kHz
Fiddle: 200 Hz to 15 kHz

The polar pattern of a mic is a graph of how well it picks up sounds coming from different directions.

• Omnidirectional picks up equally well in all directions.

• Bidirectional (figure-eight) picks up best in two directions – the front and back of the mic.

• Unidirectional picks up best in one direction – in front of the mic. Examples are cardioid, supercardioid and hypercardioid.

All else being equal, bidirectional and unidirectional patterns pick up less leakage, ambience and feedback than the omnidirectional pattern. Leakage is unwanted sound from instruments other than the one at which the mic is aimed. Ambience is the acoustics of the recording room—its early reflections and reverb. The more leakage and ambience you pick up, the more distant the instrument sounds.

An omnidirectional mic picks up more ambience and leakage than a directional mic when both are the same distance from an instrument. So an omni tends to sound more distant. To compensate, you have to mike closer with an omni. Some clip-on mics have an omni pattern. It can provide good isolation and good gain-before-feedback because the instrument is miked extremely close.


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About Bruce

Bruce Bartlett
Bruce Bartlett

Recording Engineer
   
AES and SynAudCon member Bruce Bartlett is a recording engineer, audio journalist, and microphone engineer. His latest books are “Practical Recording Techniques 5th Ed.” and “Recording Music On Location.”
http://www.bartlettaudio.com

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