Acoustic Pressure Equaliser (APE) — A smooth spherical construction with a small-diaphragm omnidirectional microphone capsule mounted flush to the surface. APEs are typically 30-50mm in diameter and serve to modify the frequency response and polar pattern through surface diffractions. These create an HF boost for on-axis sounds, and greater directivity at high frequencies giving more forward focus and, when used in a spaced array, enhanced stereo imaging. The Decca Tree is famous for using Neumann M50 microphones in which the omni capsule is embedded within a 40mm APE.

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).

A stereo microphone technique using two microphones spaced apart by at least 50cm. The microphones normally have omnidirectional polar patterns, but other polar patterns can be used. This format is known for capturing a good sense of spaciousness, depth and ambience, although spatial imaging tends to be relatively vague and potentially unstable.