Two cardioid microphones are fixed above each other so that there are no run-time differences between the capsules in the horizontal plane. Both microphones must be rotated at a certain angle from the forward direction. Typical values are 90° to 120°. In my case, a Rode NT4 stereo microphone with two capsules at a fixed angle of 90° was used. The XY method provides good results as long as the natural sound of the recording room is not to be emphasized. Another advantage is the full mono compatibility of the signal. It is possible to achieve a good positioning of the phantom source, although the signal depth is one of the weaknesses of the method. The stereo effect is generally rather unspectacular. Therefore, this setup is less suited for recording a choir since room acoustics should be emphasized.
This method was developed by engineers of the French broadcasting company. It is probably one of the most popular stereo recording techniques. Due to the good balance of run-time differences and intensity differences, this setup achieves a balanced sound, a good positioning of the phantom sources and a relatively good picture of the room acoustics. In this method, two cardioid microphones are placed at a distance of 17 cm and an opening angle of 110° to each other.
In our recording two switchable multi pattern diaphragm microphones were used (both set to cardioid pattern without any filters). Distance and angle were, however, not set with tape measurement. Hence they correspond only approximately to the ORTF requirements.
AB recording with omnidirectional mics
When two condenser mics with circular polar pattern (i.e. omnidirectional microphones) are available, then the AB technique can be used to map the depth of the recording room very well. Thanks to the excellent bass response of pressure transducers this setup produces a full-bodied sound that is ideal for large halls and churches. However, the intensity differences in intensity between the two mics are very low, so the stereo panorama is only created by recording of time differences. This can lead to a diffuse, frequency-dependent stereo image with poor sound stage reproduction. On the other hand, there are cases where this somewhat "spongy" sound is just desirable: The individual sound sources merge with one another - and that is perfect for choir recording.