Every so often you might read about an engineer recording with "baffled stereo" mic placement. Some common examples are mannequin heads with microphones in the ears, or two PZM mics taped bottom to bottom. But why do people do this? And how does it work?
The principle behind this technique is actually quite simple. If a barrier is placed between to spaced stereo mics (e.g. ORTF, NOS, spaced omnis) something interesting happens. The baffle creates an "acoustic shadow", which is just a fancy term for saying it decreases the level of off-axis bleed into the mics. The exact results vary according to microphones and spacing, but generally this process will enhance left/right channel separation. In the case of the dummy heads (more formally known as binaural microphones), headphone listeners can be convinced they are in the room! With spaced omnis, there can be an increased perception of source location in the stereo field.
