AB Stereo Microphone Technique
From WikiRecording
What is the AB Stereo Microphone Technique
A-B Stereo stereo miking technique uses two microphones, generally of omni-directional characteristic, spaced in parallel 20.3 inches - 10 feet apart to simulate a stereo field through a delay in the left or right mike (the closer microphone will receive the signal first). The resulting stereo separation is very wide.
The A-B stereo technique is wholly different in nature from XY. AB creates a stereo image through the delay and level difference in the microphones, while XY which uses cardioid or supercardioid microphones and causes the stereo effect from the decrease in off-axis volume.
A technique like ORTF combines both the (off axis, and the delayed technique to create its stereo image).
AB recording is usually used on overheads for drums or large groups of musicians or to capture the spread of a horn section or choir.
Setup
It is illustrative to imagine a small mouse singing about a foot in front of you versus a large woman. The small mouse would sound as if his voice was coming from a single point, while the large woman would appear to surround you with sound from both sides.
Issues with AB Stereo Recording
Sometimes the AB Stereo Technique results in Phase Cancellation. By nature the delay caused by the signal reaching the microphones at different times can cause phase problems but for the most part this is a small and for the most part avoidable problem with proper placement. Though if you are bouncing down to mono, XY or midside (MS) is probably a preferable technique.
