Stereo Miking
XY gives you level differences only. Spaced pair gives you time differences only. ORTF and Mid-Side give you both, and that's why they sound more natural.
Two Mics, One Image
Stereo recording uses two microphones to capture the spatial position of sounds. The stereo image depends on two cues: level differences (which mic is louder) and time differences (which mic hears the sound first). Different stereo miking techniques exploit these cues in different combinations.
XY: Coincident Pair
Two cardioid mics with capsules nearly touching, angled apart (typically 90–135°). Because the capsules occupy the same point in space, there are no time differences, only level differences from the polar patterns. This gives excellent mono compatibility but a narrower stereo image.
When you select XY and drag the source, notice only the level changes between L and R. The sound arrives at both mics at the same instant because they're touching.
Spaced Pair
Two omnidirectional mics placed some distance apart (typically 40–60 cm). Because sound arrives at each mic at different times, this creates time differences. The result is a wide, spacious image, but when summed to mono, the time differences cause comb filtering.
Hit the Mono button with Spaced Pair. Hear the comb filtering? That's time differences cancelling frequencies when summed.
ORTF
Two cardioid mics with capsules 17 cm apart, angled 110° (developed by French national radio). This combines both level and time differences for a natural stereo image with good mono compatibility.
ORTF gives you both cues. It's designed to match how human ears work (17 cm apart, angled outward).
Mid-Side (M/S)
A cardioid mic (mid) and a figure-8 mic (side). To decode: L = M + S, R = M − S. The side mic controls stereo width. Perfectly mono-compatible: the side signal cancels completely in a mono sum, leaving only the mid.
The Side mic captures only the difference between left and right. In mono, it cancels completely for perfect mono compatibility.
Try it: move the source around and compare how each technique images it. Hit the mono check button on spaced pair to hear the comb filtering.