The choice of technique depends on a number of factors, including: There are several classes of microphone placement for recording and amplification.
When the microphones are bidirectional and placed facing ±45° with respect to the sound source, the X-Y-setup is called a Blumlein pair.
The sonic image produced by this configuration is considered by many authorities to create a realistic, almost holographic soundstage.
They added a little in-phase crosstalk above 700 Hz to better align the mid and treble phantom sources with the bass ones.
Mid/side coincident technique employs a bidirectional microphone (with a figure of 8 polar pattern) facing sideways and a cardioid (generally a variety of cardioid, although Alan Blumlein described the usage of an omnidirectional transducer in his original patent) facing the sound source.
The capsules are stacked vertically and brought together as closely as possible, to minimize comb filtering caused by differences in arrival time.
X-Y microphone capsules can be mounted in one unit, or even on the top of a handheld digital recorder.
M/S arrays can be very compact and fit easily into a standard blimp windscreen, which makes boom-operated stereo recordings possible.