1. X/Y
The X/Y technique will provide a stereo image of about 90-130 degrees. Two cardioid microphones are set up in an ‘X’ formation directly above each other. Usually, the bottom microphone is at 90 degrees to the top microphone, meaning it’s perpendicular. However, you can angle it so it's closer or further apart depending on how much stereo imaging you want.
2. Spaced Pair (A/B)
In the spaced pair technique (sometimes referred to as an A/B stereo pair), the same two microphones are placed next to each other spaced apart rather than directly above each other. This method creates a much wider stereo image than the X/Y setup, but it can also risk capturing more background noise (particularly if you’re recording outdoors or in a large room).
For advanced setups that require more microphones there are two main techniques you can use.
1. ORTF
The ORTF recording method is a spaced pair variation utilizing two cardioid microphones (or hypercardioid) set at a fixed 110 degree from each other, at a distance of 17 centimeters. The ORTF technique gives you a broad stereo image that falls to about 80 Hz, where it narrows in and you begin to lose the stereo effect of sounds from the outer edges.
2. Blumlein Pair
The Blumlein Pair method employs two matched figure-of-eight microphone capsules in a coincident pair (one microphone directly in front of the other). The capsules are oriented at a 90-degree angle relative to each other, one vertical, one horizontal. With all cardioid microphones and most hypercardioids being considered "figure-of-eight" microphones when the polar plot is flipped on its side by 180 degrees, both cardioids or both hypercardioids can work in this technique in a "pseudo Blumlein Pair."