1
XY (Coincident Pair)
XY is a coincident stereo technique: two cardioid mics with their capsules stacked at the same point, angled 90-135° apart. Because the capsules share one point in space, sound reaches both at the same instant, there are no time-of-arrival differences.
That is why XY is fully mono-compatible: collapse it to mono and nothing cancels. The trade is a somewhat narrower stereo image than spaced techniques.
In practice: Recording a band for both a mono FM broadcast and a stereo release: XY guarantees the mono fold-down stays clean, no phase cancellation.
XY = coincident cardioids, narrower image but bulletproof in mono.
2
ORTF (Near-Coincident)
ORTF is a near-coincident stereo technique: two cardioids spaced 17 cm apart at a 110° angle. The 17 cm roughly matches the gap between human ears, so the pair captures both level differences and small time-of-arrival differences, the same two cues your ears use.
The result is a wider, more natural "you are there" image than XY, while staying reasonably mono-safe.
In practice: Capturing a seated acoustic ensemble so it sounds like being in the room: an ORTF pair a few feet in front delivers that natural width.
ORTF = near-coincident cardioids (17 cm, 110°): natural, room-like width.
3
Spaced Pair (A/B)
A spaced pair (A/B) places two mics, often omnis, several feet apart. With that much distance, the stereo image comes entirely from time-of-arrival differences, producing a wide, enveloping, spacious sound.
The catch is the flip side of that: relying purely on timing means it does not fold down cleanly to mono, summing causes comb filtering. Use it when width matters and mono compatibility does not.
In practice: A solo guitarist in a beautiful church, stereo release only: a spaced omni pair captures the room's width gorgeously, just do not expect a clean mono fold-down.
Spaced pair = wide and enveloping, but not mono-safe.
4
Mid-Side (M/S)
Mid-Side records two mics at one point: a "mid" mic (usually cardioid) pointed at the source, and a "side" mic (figure-8) aimed sideways. They are decoded into left/right afterward, and crucially, the stereo width is adjustable in the mix by changing how much side signal you add.
It is the ultimate hedge: the mid channel alone is a perfect mono recording, so you can decide on width, or mono, long after the session.
In practice: Recording a guitar before knowing if it will be panned center or spread wide: M/S lets you dial any width later, or just use the mid for flawless mono.
Mid-Side = stereo width you set after recording; the mid alone is perfect mono.
5
Blumlein Pair
A Blumlein pair is two figure-8 mics, coincident, at 90° to each other. Because figure-8 mics hear front and back equally, the pair captures the direct sound up front and the room's reflections from behind, a strikingly realistic, phase-coherent stereo image.
That rear pickup is the key consideration: Blumlein only sounds great in a room that sounds great. In a dead or bad room it has nothing good to capture from behind.
In practice: A string quartet in a hall with gorgeous natural reverb: a Blumlein ribbon pair captures the ensemble and the hall together in one coherent image.
Blumlein = crossed figure-8s, superbly realistic, but only in a good room.
6
The 3:1 Rule
When two mics pick up the same source, the 3:1 rule keeps them from fighting: the distance between the two mics should be at least three times each mic's distance to its own source.
That spacing makes the bleed into the "wrong" mic quiet enough that the time-of-arrival difference does not cause audible comb filtering when the mics are combined.
In practice: Three players each miked 8 inches away but standing close together, and the mix sounds hollow: their mics need to be at least 24 inches apart, 3x the source distance.
3:1 rule: space mics at least 3x their distance-to-source apart to avoid combing.
7
Phase Checking Multi-Mic Setups
Whenever two mics capture one source from different distances, the sound reaches them at slightly different times and the mics can fight when summed, comb filtering that thins the tone. The quick test: flip the polarity on one channel; if the low end vanishes the mics were in phase (flip it back), if it fills out, leave it.
Beyond that, zoom into the waveforms and nudge the farther mic earlier so the transients line up.
In practice: Two mics on a guitar that sound thinner combined than either alone: flip polarity to test, then time-align the waveforms in the DAW.
Two mics, one source: test polarity and time-align the waveforms.
8
Comb Filtering
Comb filtering happens when a signal is mixed with a slightly delayed copy of itself. At some frequencies the two add; at others they cancel, producing a row of evenly spaced peaks and notches that looks like a comb. The sound goes hollow, thin, or "phasey".
It is the hidden cause behind a lot of bad multi-mic recordings: two mics on one source, or a mic plus a nearby reflection, arrive at slightly different times and comb-filter when summed.
In practice: An acoustic guitar recorded with two mics at different distances sounds hollow in mono, the arrival-time gap is combing. Time-align the tracks, or use one mic.
A signal plus a delayed copy of itself = hollow, combed sound.
9
Spaced Pair vs XY vs ORTF: Width vs Mono Compatibility
Stereo techniques trade width against mono compatibility. A spaced pair (A/B) gives the widest image using time-of-arrival differences, but those differences cause phase cancellation when summed to mono, so its mono compatibility is worst. XY uses coincident capsules and level differences only: best mono compatibility, narrowest image. ORTF (17 cm at 110°) uses both, a good compromise.
Choose by delivery: if mono playback is likely, favor XY or ORTF.
In practice: Recording an acoustic act for streaming where phone-speaker mono playback is likely: ORTF over a spaced pair, you keep useful width without the mono cancellation.
Spaced pair = widest, worst mono; XY = narrowest, best mono; ORTF = the compromise.
These lessons are the teach side of knowledge cards from the Studio Mix deck. In the daily plan each one is followed by a quiz, spaced over weeks, so it stays known rather than read once.