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Dr Harvey Fletcher (1884 – 1981) was an American physicist working for Bell Laboratories on the development of  Stereophonic Sound, amongst other things, in the early 1930s. He was a contemporary of Alan Blumlein but was developing stereo techniques entirely independently.

See Double Mid-Sides Array

An approach to capturing and reproducing stereophonic sound developed by Dr Harvey Fletcher (of Bell Labs in America) in the early 1930s. A multiplicity of microphones arrayed in front of a large ensemble sample the audio wavefront at different points in space. Each microphone is connected to a corresponding loudspeaker in front of the audience to recreate the same wavefronts. Although effective, this technique was deemed highly impractical at the time, and it evolved through simplification into various spaced-omni microphone techniques.

Denoted as dc. The distance from a directional sound source at which the sound pressure level of the direct sound exactly equals that of the reverberant sound. Dc is dependent on the geometry and absorption characteristics of the space in which the sound waves propagate such that a highly reverberant space has a relatively short dc, whereas a dry-sounding room has a long dc. Critical distance is important in determining where to locate microphones to achieve a desired perspective.

A stereo microphone technique made popular by the esteemed British recording engineer, Tony Faulkner. Similar in appearance to the OCCO array, it uses a pair of near-spaced cardioid microphones flanked by a pair of spaced omnidirectional mics. The cardioid pair has a capsule spacing of around 41cm while the omnis are spaced at 67cm. Both pairs have 90° mutual angles.

Faulkner explains the concept as being similar to steerable radio-frequency aerial arrays, whereby the reception beam focus is orientated by manipulating the relative phases of signals from each aerial element — although that’s not how the microphones are actually used in this array as there is no direct phase manipulation!

Another stereo mic array associated with Faulkner, and sometimes also called a ‘phased array’ employs a pair of figure-of-eight microphones spaced 20cm apart both facing directly forward (mutual angle 0°). This is essentially a spaced-omni array but designed to minimise unwanted side reflections in acoustically difficult venues by replacing the omnidirectional microphones with figure-of-eight types.

A complex multi-mic stereo array typically combining two or more conventional stereo arrays mounted in the same plane. The OCCO array and Falkner Phased array are examples combination arrays, where a near-coincident array is combined with a spaced-omni array with the aim of blending the spatial imaging accuracy of the former with the spaciousness and low-frequency extension of the latter.

The historical research centre of the Bell Telephone Company in America, and credited with (amongst many other inventions) the development of early stereo spaced array microphone techniques concurrent with, but independent of, Blumlein’s work at EMI in the UK.

Elements of acoustic sound signals detected by the ears and brain which help to locate sound sources in the space around the listener using inter-aural time differences (ITD), inter-aural level differences (ILD), and spectral anomalies due to comb-filtering caused by the pinnae and shoulders.

The differences between the relative angles of physical sound sources placed in front of a stereo microphone array and their representation as virtual sources on replay from stereo loudspeakers. Most stereo arrays tend to expand the relative angles of sources close to the centre but compress them for sources close to the edge ( somewhat like a wide-angle lens).