Stereo Techniques

XY, ORTF, AB and MS trade width against phase and mono compatibility.

Related

Stereo TechniquePhaseChoir scoring

The problem

One microphone gives a single point and no sense of width. Two microphones introduce a time difference that cancels some frequencies. A stereo technique is a choice between those problems. None of them delivers maximum width, stability and mono compatibility at once.

Signal chain

XY places two capsules together, so only level differs and mono compatibility is best. ORTF spaces them 17 cm apart at 110 degrees, combining level and time differences. AB uses a wider spacing where time dominates; it is wide but thins out in mono. MS uses a forward cardioid and a sideways figure-eight, with width adjustable at decode.

Placement and settings

Set XY between 90 and 135 degrees, aimed at the centre of the source. Keep ORTF at 17 cm and 110 degrees. Start AB at 40 to 60 cm and widen for a larger source. For MS, point the side capsule at the sides and the mid capsule forward, then decode with M+S and M-S.

What to listen for

Switch to mono and hear whether the centre thins and the low end survives. Then listen for continuity as the source moves across the image. More width is not automatically better; stability matters more.

Common misconceptions

• Wider spacing always gives better width → too much time difference causes stronger mono cancellation.
• ORTF is a kind of AB → it is a combined angle-and-spacing array.
• MS needs three microphones → two are enough, one mid and one side.

Sources

• Streicher and Dooley, Basic Stereo Microphone Perspectives, AES preprint
• Eargle, The Microphone Book, 3rd ed., stereo array chapters

Used for fact-checking only; all prose is original.