The spaced omni technique places omnis at a distance of 1/3 to 1/2 of the sound stage width from each other

together to create one side of the stereo signal, and subtracts the side signal from the mid signal to create the other.The result is a very accurate translation of the stereo listening field. The presence of an M-S balance control in the encoder also allows the engineer to control the ratio of mid signal to side signal, and therefore the perceived width of the stereo field.

Sou

n

d

M

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Note that Mid-Side is the only stereo miking technique

+S

-S

that does not rely explicitly on a matched pair of

 

 

microphones. However, high quality microphones are

The Mid-Side technique electronically

imperative for overall sonic integrity, as well as to ensure

well-balanced capsules within the figure 8 mic. Note also

derives a stereo signal from a center mic

that Mid-Side offers a great deal of flexibility because the

coincident with a figure 8

 

 

mid does not have to be a cardioid. If more audience noise or reflections from the back of the room are desired, an omni could be used as the mid mic to great effect.The Mid-Side technique also offers excellent mono compatibility because the recombination of the two out-of-phase side signals

cancels them out to leave only the mid or center signal.This process simultaneously minimizes side

reflections that can yield confusion in a mono conversion.

 

Spaced Omni

 

The spaced omni technique is often used for recording

 

orchestras. It employs a matched pair of omni mics typically

Sound Source

positioned four to eight feet in front of the sound source.

 

The mics are normally at the same height as the

 

performers, although raising them to 10 feet or more in

 

the air can increase perceived ambience. The distance

D

between the mics should be approximately 1/3 to 1/2 the

 

width of the sound stage. While spaced omni provides

2 3

 

D~ D

excellent depth and stereo image, the center of the field can tend to be less distinct. In situations where there is too much unwanted background noise or the mics must be placed further away due to logistics, experiment with using carefully placed cardioids or supercardioids with this spaced mic technique.

As pointed out earlier, spaced miking techniques are not as technically accurate as some correlated miking techniques. They can be susceptible to phase anomalies owing to reflections entering the mics from various surfaces in the recording environment￿although some people actually find this pleasing. Many engineers consider spaced mic techniques best for recording relatively uncorrelated sounds such as a pipe organ or outdoor ambience. Spaced techniques are also useful in creating

the surround channels for surround sound.

Decca Tree

Staff engineers at Decca RecordsDecca(nowTreeThorn-EMI)

developed a technique known as thein England in the 1950s.This method and numerous variations are still very popular today in the recording of film scores.

Sound Source

conductor

A T-shaped fixture houses a microphone￿classically an omni￿at each of its three ends.The two mics at either end of the cross-arm are positioned approximately two meters (approx. 79 inches) apart, while the central microphone is

1.5meters (59 inches) away at the bottom of the T. This structure is then mounted about eight to ten feet in the air and positioned so that the central mic is just behind the conductor￿s head. The mics are tilted down at about 30

1.5 m

2 m

The Decca Tree technique is very

popular in film scoring

Choosing & Using Microphones

23

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Image 23
M-Audio Microphone manual Spaced Omni, Decca Tree