Stereo Microphone Techniques: XY, ORTF, NOS, AB and Mid-Side

Two microphones can capture anything from a focused, almost mono image to a wonderfully spacious performance. The difference is often just spacing and angle. We’ll compare XY, ORTF, NOS, AB and Mid-Side, explain what each does well, and show how to avoid getting an impressive stereo image that falls apart in mono.

Coincident XY

With XY, two directional microphones have capsules positioned as close together as practical while pointing in different directions—often around 90 degrees apart. Level differences between channels create most of the stereo image. XY is compact and generally offers strong mono compatibility, although a narrow image can result from some arrangements.

ORTF

ORTF typically uses two cardioids spaced 17 cm apart and angled 110 degrees. This combination produces interchannel time and level differences, often yielding a spacious yet reasonably well-defined stereo image.

NOS

NOS uses two cardioids spaced 30 cm apart and angled 90 degrees. Relative to ORTF it places greater emphasis on spacing. The outcome depends on distance, source width, and room reflections; the numbers are a starting geometry, not a guarantee of a preferred sound.

Spaced pair (AB)

AB places two microphones apart, frequently omnidirectional models. Spacing can capture a broad sense of ambience and low-frequency extension, but interchannel arrival-time differences can create comb filtering when collapsed to mono. Always audition the mono sum before committing.

Mid-Side (MS)

MS combines a forward-facing mid microphone with a sideways figure-eight side microphone. Decode it as Left = Mid + Side and Right = Mid − Side. The relative side level adjusts stereo width after recording; the mid signal can also provide a straightforward mono reference. Ensure the figure-eight polarity and channel routing are correct.

Common stereo microphone starting geometries

Technique	Spacing	Included angle / orientation	Useful characteristic
XY	Capsules as coincident as practicable	Often 90° between cardioid axes	Primarily level differences; good mono behavior
ORTF	17 cm	110° between cardioids	Time and level cues
NOS	30 cm	90° between cardioids	Broader time differences
AB	Variable	Usually parallel omnis	Spaciousness; mono summing requires care
MS	Coincident	Forward Mid + sideways figure-eight Side	Width adjustable when decoded

Choosing a setup

For controlled localization and mono compatibility, begin with XY or MS. For naturally spaced ensembles where a wider room impression is desirable, compare ORTF and NOS. AB can be effective for ambience and larger sources when mono behavior is acceptable. Record the same musical passage with several configurations if possible, keep levels matched, and listen both in stereo and mono.

Practical checks

Match microphone types and gain when the technique requires symmetry. Measure capsule locations, not the edges of the microphone bodies. Watch for stands obstructing one capsule, asymmetric reflections, and accidental channel reversal. Document microphone angles, spacing, height, and source distance so successful results can be repeated.