XY Stereo is a stereo micing 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.