# Engineering Acoustics/Microphone Technique

## General Technique

1.  A microphone should be used whose frequency response will suit the
    frequency range of the voice or instrument being recorded.
2.  Vary microphone positions and distances until you achieve the
    monitored sound that you desire.
3.  In the case of poor room acoustics, place the microphone very close
    to the loudest part of the instrument being recorded or isolate the
    instrument.
4.  Personal taste is the most important component of microphone
    technique. Whatever sounds right to you, *is* right.

## Working Distance

### Close Miking

When miking at a distance of 1 inch to about 3 feet from the sound
source, it is considered close miking. This technique generally provides
a tight, present sound quality and does an effective job of isolating
the signal and excluding other sounds in the acoustic environment.

#### Leakage

Leakage occurs when the signal is not properly isolated and the
microphone picks up another nearby instrument. This can make the mixdown
process difficult if there are multiple voices on one track. Use the
following methods to prevent leakage:

-   Place the microphones closer to the instruments.
-   Move the instruments farther apart.
-   Put some sort of acoustic barrier between the instruments.
-   Use directional microphones.

#### 3 to 1 Rule

The 3:1 distance rule is a general rule of thumb for close miking. To
prevent phase anomalies and leakage, the microphones should be placed at
least three times as far from each other as the distance between the
instrument and the microphone.

!3:1 Rule

### Distant Miking

Distant miking refers to the placement of microphones at a distance of 3
feet or more from the sound source. This technique allows the full range
and balance of the instrument to develop and it captures the room sound.
This tends to add a live, open feeling to the recorded sound, but
careful consideration needs to be given to the acoustic
environment.

### Accent Miking

Accent miking is a technique used for solo passages when miking an
ensemble. A soloist needs to stand out from an ensemble, but placing a
microphone too close will sound unnaturally present compared the distant
miking technique used with the rest of the ensemble. Therefore, the
microphone should be placed just close enough to the soloist that the
signal can be mixed effectively without sounding completely excluded
from the ensemble.

### Ambient Miking

Ambient miking is placing the microphones at such a distance that the
room sound is more prominent than the direct signal. This technique is
used to capture audience sound or the natural reverberation of a room
or concert
hall.

## Stereo and Surround Technique

### Stereo

Stereo miking is simply using two microphones to obtain a stereo
left-right image of the sound. A simple method is the use of a spaced
pair, which is placing two identical microphones several feet apart and
using the difference in time and amplitude to create the image. Great
care should be taken in the method as phase anomalies can occur due to
the signal delay. This risk of phase anomaly can be reduced by using the
X/Y method, where the two microphones are placed with the grills as
close together as possible without touching. There should be an angle of
90 to 135 degrees between the mics. This technique uses only amplitude,
not time, to create the image, so the chance of phase discrepancies is
unlikely.

!Spaced Pair !X/Y
Method

### Surround

To take advantage of 5.1 sound or some other surround setup, microphones
may be placed to capture the surround sound of a room. This technique
essentially stems from stereo technique with the addition of more
microphones. Because every acoustic environment is different, it is
difficult to define a general rule for surround miking, so placement
becomes dependent on experimentation. Careful attention must be paid to
the distance between microphones and potential phase anomalies.

## Placement for Varying Instruments

### Amplifiers

When miking an amplifier, such as for electric guitars, the mic should
be placed 2 to 12 inches from the speaker. Exact placement becomes more
critical at a distance of less than 4 inches. A brighter sound is
achieved when the mic faces directly into the center of the speaker cone
and a more mellow sound is produced when placed slightly off-center.
Placing off-center also reduces amplifier noise.

### Brass Instruments

High sound-pressure levels are produced by brass instruments due to the
directional characteristics of mid to mid-high frequencies. Therefore,
for brass instruments such as trumpets, trombones, and tubas,
microphones should face slightly off of the bell\'s center at a distance
of one foot or more to prevent overloading from windblasts.

### Guitars

Technique for acoustic guitars is dependent on the desired sound.
Placing a microphone close to the sound hole will achieve the highest
output possible, but the sound may be bottom-heavy because of how the
sound hole resonates at low frequencies. Placing the mic slightly
off-center at 6 to 12 inches from the hole will provide a more balanced
pickup. Placing the mic closer to the bridge with the same working
distance will ensure that the full range of the instrument is captured.

Some people prefer to use a contact microphone, attached (usually) by a
fairly weak temporary adhesive, however this will give a rather
different sound to a conventional microphone. The primary advantage is
that the contact microphone performance is unchanged as the guitar is
moved around during a performance, whereas with a conventional
microphone on a stand, the distance between microphone and guitar would
be subject to continual variation. Placement of a contact microphone can
be adjusted by trial and error to get a variety of sounds. The same
technique works quite well on other stringed instruments such as
violins.

### Pianos

Ideally, microphones would be placed 4 to 6 feet from the piano to allow
the full range of the instrument to develop before it is captured. This
isn\'t always possible due to room noise, so the next best option is to
place the microphone just inside the open lid. This applies to both
grand and upright pianos.

### Percussion

One overhead microphone can be used for a drum set, although two are
preferable. If possible, each component of the drum set should be miked
individually at a distance of 1 to 2 inches as if they were their own
instrument. This also applies to other drums such as congas and bongos.
For large, tuned instruments such as xylophones, multiple mics can be
used as long as they are spaced according to the 3:1 rule.

### Voice

Standard technique is to put the microphone directly in front of the
vocalist\'s mouth, although placing slightly off-center can alleviate
harsh consonant sounds (such as \"p\") and prevent overloading due to
excessive dynamic range. Several sources also recommend placing the
microphone slightly above the mouth.

### Woodwinds

A general rule for woodwinds is to place the microphone around the
middle of the instrument at a distance of 6 inches to 2 feet. The
microphone should be tilted slightly towards the bell or sound hole, but
not directly in front of it.

## Sound Propagation

It is important to understand how sound propagates due to the nature of
the acoustic environment so that microphone technique can be adjusted
accordingly. There are four basic ways that this occurs:

### Reflection

Sound waves are reflected by surfaces if the object is as large as the
wavelength of the sound. It is the cause of echo (simple delay),
reverberation (many reflections cause the sound to continue after the
source has stopped), and standing waves (the distance between two
parallel walls is such that the original and reflected waves in phase
reinforce one another).

### Absorption

Sound waves are absorbed by materials rather than reflected. This can
have both positive and negative effects depending on whether you desire
to reduce reverberation or retain a live sound.

### Diffraction

Objects that may be between sound sources and microphones must be
considered due to diffraction. Sound will be stopped by obstacles that
are larger than its wavelength. Therefore, higher frequencies will be
blocked more easily that lower frequencies.

### Refraction

Sound waves bend as they pass through mediums with varying density. Wind
or temperature changes can cause sound to seem like it is literally
moving in a different direction than expected.

## Sources

-   Huber, Dave Miles, and Robert E. Runstein. *Modern Recording
    Techniques*. Sixth Edition. Burlington: Elsevier, Inc., 2005.
-   Shure, Inc. (2003). *Shure Product Literature.* Retrieved November
    28, 2005, from
    <http://www.shure.com/scripts/literature/literature.aspx>.

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