This group of articles describes microphone techniques for two-channel stereo recordings. This includes both spaced set of microphones and coincident pairs.
Keywords: Microphone techniques, AB, baffled stereo, ORTF, DIN, NOS, XY, Blumlein, MS, and binaural.

Achieved knowledge: You know how the setup is done and know about advantage and disadvantages of the various setups.

How to determine spacing and angling

The stereophonic recording techniques are based on the knowledge of how directional information is perceived by the human hearing system: When reproduced by loudspeakers in a two-channel system, the first arriving, and/or the strongest sound produces this directional information to the listener.

Psychoacoustic research has quantified the time and level differences adequate for directional imaging to any position on the line between left and right loudspeaker in a standard loudspeaker setup.

The result can be seen from the curves in (fig. 2). If no time or level differences between left and right are present, the sound source is reproduced at 0° (hard center). To make a sound source appear at 30°, the level difference between left and right channel should be 15 dB. Also the sound appears at 30° if the time difference between left and right channel is 1.12 ms (milliseconds).

Additionally, a combination of time difference and level difference can act together. For instance the sound will be reproduced at 30° if the signal in one channel is delayed by 0.5 ms and the level is approximately 6 dB below the other channel (see dotted lines in fig. 2).

As mentioned, stereo recording is not just a question of reproduction at hard left or right. Naturally the "in-between" distribution is important, otherwise angle distortion will occur (fig. 3).

In fig. 2 the inter channel differences adequate for 10° and 20° reproduction respectively are also found.

First quantified, this information can be combined with the directional characteristics of the units in a two-microphone setup. Then it is possible to determine the optimum positioning of the microphones for a stereo recording.

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A-B Stereo
Decca Tree
ORTF Stereo
DIN Stereo
NOS Stereo
XY Stereo
Blumlein Stereo
MS Stereo