Stereo microphones use a specific technique that involves a combination of two microphone capsules into a single housing for conventional stereo recordings. The most common combination for this is condenser microphones, dynamic microphones, and ribbon microphones.
Stereo Microphones: Stereo Milking
Stereo miking is a widely popular technique. It uses a combination of microphones that create a stereo image. Then, this stereo image can provide depth and spacial placement to either a single instrument or to the overall recording. Although there are a variety of techniques in stereo milking, the most popular ones are the spaced pair (A/B configuration), the coincident or near-coincident pair (X-Y configuration), and the mid-side (M-S configuration).
Spaced Pair Technique (A/B Configuration)
The spaced pair technique is common in soundtrack playback and in broadcast. It involves two cardioid or two omnidirectional microphones spaced far from each other. In this technique, the microphones are panned in a left/right configuration to capture the complete stereo image of a specific arrangement of instruments or an instrument by itself.
Not everything is nice and dandy, though. Sometimes the configuration shifts to mono and the frequencies overpass the sound. Thus, a problem emerges. This conflict is usually quite serious, especially when the user decides to play the recording on mono.
Coincident or Near-coincident Pair Technique (X-Y Configuration)
The X-Y technique, also known as coincident or near-coincident pair, uses two identical cardioid microphones. It involves two microphone capsules placed very close together or somewhat distant from each other. That is, coincident and near-coincident, respectively. Depending on the size of the sound source and the desired sound, the microphones are facing each other at a specific angle. Usually, both microphones face directly at the center of the sound source. Similarly, their pan is to the left and to the right.
Due to the small distance between the microphones, the sound arrives at the same time to both devices. Because of this, the conflicts that the A/B technique caused are neither reduced or completely eliminated. The stereo separation technique is efficient, but it has its limits. The latter case occurs if the sound source is larger than average. It’s worth mentioning that mono-compatibility can range from near-coincident to coincident.
Mid-side Stereo Technique (M-S Configuration)
The M-S technique, also known as mid-side stereo technique, involves one cardioid microphone element and a bi-directional microphone one. These microphones are typically placed and organized in a coincident way. Usually, the cardioid microphone faces directly at the sound source and picks up on-axis sounds. The bi-directional microphone, positioned on the side, faces left and right and picks up an off-axis sound. The mid-side matrix joins the two signals, offering a variable-controlled stereo image. By adjusting both signals, the player is able to create a narrower or a wider image without touching the microphone. This technique is completely mono-compatible and used in broadcast and film applications frequently.
Stereo Microphones: Conclusions
As you can see, stereo microphones have specific usages. This journey aims to be a guide for you to better understand these microphones’ basics!