Manual

NEAR-COINCIDENT MICROPHONE TECHNIQUES

These techniques provide good positional information together with a satisfying sense

of space as they rely on both intensity and phase differences. The microphones are

set close enough together to be effectively coincident at low frequencies and far

enough apart for there to be a time delay between sounds from the left and right

extremes of the sound source. Because of the spacing between the capsules, large

image shifts can stem from quite small movements within the sound source, hence,

close miking is not advisable. (Also, sounds arriving from the extremes of the sound

source may cause problems when deriving a compatible mono signal and when disc

cutting.)

There are four main near-coincident techniques:

• The ORTF technique was developed by the French broadcasting

organisation. Two cardioid microphones are spaced 170 mm apart with an

included angle of 110°.

• The NOB system was developed by the Dutch broadcasting organisation.

Two cardioid microphones are spaced 300 mm apart with an included angle of 90°.

• A system developed by Faulkner uses two forward-facing figure-of-eight

microphones spaced 200 mm apart. The microphones are positioned further back

from the sound source than is usual with other near-coincident techniques. The

results show many of the qualities of the Blumlein technique and a natural balance

between close and distant elements within the sound source.

• The binaural technique was specially developed for listening to playback on

headphones but the recordings are considered by some listeners to be

unsatisfactory when heard on loudspeakers. This system uses a 'dummy head',

usually made from polystyrene, with omnidirectional microphones placed into the

'ears'. This technique provides excellent imaging in both horizontal and vertical

planes. A development of the technique uses two omnidirectional or figure-of-

eight microphones set approximately 90 mm on either side of a circular, non-

reflective baffle. This allows sufficient 'leakage' between the microphones to make

reproduction over loudspeakers a satisfying experience.

In recent times attempts have been made to bring to loudspeaker listening the

naturalness, and the depth and sense of space present when listening on

headphones to dummy-head recordings. These features are usually missing from

recordings made with coincident X-Y microphones. To this end, it is necessary that

the signals have a natural interaural relationship, but this can only be achieved

with some form of

dummy-head technique.

The Schoeps KFM6U sphere microphone has been designed to satisfy these

requirements. A 180 mm diameter sphere has two omnidirectional microphones set

on opposite sides of the sphere and produce a stereo signal with natural interaural