A stereo miking technique that employs two cardioid microphones angled 90 degrees from each other, but positioned at the same point (or as near as their physical size will allow). Theoretically, the two microphone capsules need to be at exactly the same point to avoid any phase problems due to the distance between the capsules. As this is not possible, the best approximation to placing two microphones at the same point is to put one microphone on top of the other with the diaphragms vertically aligned. In this way, sound sources in the horizontal plane will be picked up as if the two microphones are placed at the same point.
The stereo image is produced by the off-axis attenuation of the cardioid microphones. While A-B stereo is a difference-in-time-stereo, the XY stereo is a difference-in-level stereo. But as the off-axis attenuation of a typical cardioid microphone is only around 6dB at 90 degrees, the channel separation is limited, and wide stereo images are not possible with this recording method. Therefore, XY stereo is often used where high mono-compatibility is needed – for example, in broadcasting situations where many listeners still receive the audio on mono equipment. Since the sound-sources are mainly picked up off-axis when using the XY stereo setup, high demands are placed on the off-axis response of the microphones used.