The most commonly used X-Y microphone technique is known as the "X-Y stereo microphone technique" or simply "X-Y stereo." It involves placing two microphones very close together, typically at a 90-degree angle, with their capsules aligned as closely as possible. This technique is used to capture a stereo image of sound, providing a sense of width and space in the recorded audio.
The X-Y stereo technique is popular because it offers good mono compatibility (meaning the recording sounds acceptable when played through a single speaker), and it provides a simple and effective way to capture a balanced stereo image with minimal phase issues. This technique is often used in various audio recording situations, such as music recording, field recording, and live sound reinforcement, to capture a natural and accurate stereo soundstage.