Stereo microphone technique
A stereo microphone technique combines two mic capsules in a single housing for conventional stereo recording. Moreover, microphones used for combination can vary from a condenser, dynamic, ribbon microphones, etc.
One of the most popular specialized microphone techniques is stereo miking. The use of two or more microphones to create a stereo image will often give depth and spatial placement to an instrument or overall recording. There are some different methods for stereo. Three of the most popular are the spaced pair (A/B), the coincident or near-coincident pair (X-Y configuration), and the MD-side (M-S) technique.
The spaced pair technique
The spaced pair (A/B) technique uses two cardioid or omnidirectional microphones. Furthermore, they are spaced 3 to 10 feet apart from each other panned in left/right configuration to capture the stereo image of an ensemble or instrument. Effective stereo separation is very wide. When the program switches to mono and frequencies jump out or fall out of the sound, you can assume that there is a phase problem. This may be a serious problem if you play your recording in mono. Finally, this is typical in broadcast or soundtrack playback.
The X-Y technique uses two cardioid microphones of the same type and manufacture. They have two mic capsules placed either as close as possible (coincident) or within 12 inches of each other (near-coincident). Also, they are facing each other at an angle ranging from 90 -to135 degrees, depending on the size of the sound source and the particular sound desired. The pair is placed with the center of the two mics facing directly at the sound source and panned left and right. Due to the small distance between the microphones, sound arrives at the mics at nearly the same time. This reduces (near coincident) or eliminates (coincident) the possible phase problems of the A/B techniques.
The stereo separation of this technique is good but may be limited if the sound source is extremely wide. Mono compatibility is fair (near-coincident) to excellent (coincident).
Mid-side stereo technique
The M-S or mid-side stereo technique involves a cardioid mic element and a bi-directional mic element. What’s more, they are usually housed in a single case, mounted in a coincident arrangement. The cardioid (mid) faces directly at the source and picks up primarily on-axis sound while the bi-directional (side) faces left and right and picks up an off-axis sound. The M-S matrix combines the two signals to give a variable controlled stereo image.
By adjusting the level of mid versus side signals, you can create a narrower or wider image without moving the microphone. This technique is entirely mono-compatible and producers and engineers widely use it in broadcast and film applications.
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