Just as there is a wide range of microphones available on the market, there are also a wide range of accepted mic placement configurations for stereo recording. This section discusses four of the most common or interesting of these configurations: AB, XY, MS, and binaural.
The AB configuration is the simplest of them all. It combines two cardioid microphones spaced several feet apart and facing forward, at slight angles to one another. One particular problem with this configuration is that it is subject to phase problems. Essentially, as sound waves travel to the two microphones, they may arrive at each out of phase with the other. As a result, one may experience constructive and destructive interference that can appear as a beat frequency in the recording. (The beat frequency is correlated to the distance between the microphones, and will tend to be more noticeable at greater distances.)
The XY configuration defeats the beat frequency problem by placing the two cardioid microphones very close together, coincident at 90o. In comparison to the AB configuration, this can result in a greater overlap in the response areas of the two microphones. However, since the transducers of the two mics are side-by-side, the phase difference between the two microphones is negligible.
The Mid./Side (MS) configuration is perhaps one of the most interesting of the more common recording configurations. It combines two types of microphones, a cardioid or omnidirectional mic with a figure-eight microphone. The cardioid/omni mic is placed in the middle facing straight forward, while the figure-eight mic is placed facing ninety degrees to the side. (A figure-eight mic is essentially a stereo microphone in which the left and right channels each have a transducer facing 180o from one another. Since it is a stereo mic, the left and right channels are distinct from one another.) When is added to the forward lobe of the figure-eight, you get the left pickup. When the cardioid/omni is subtracted from the rear lobe, which 180o out of phase with the forward lobe, you get the right pick up. The advantage of this configuration is that it can be combined onto a single mic stand, and it is argued that because the cardioid/omni is facing directly forward, it will better pick up the center sounds.
The binaural configuration is an old but infrequently used configuration these days. However, many would argue that it allows for the most accurate reproduction of a performance. Simply put, a binaural arrangement places omnidirectional microphones on a dummy head made to the proportions of an average human head, including many of the attributes such as the softness of the flesh, the hardness of the bones within, and even the presence of hair, all of which can affect the characteristics of the sound being recorded. The attempt, as you may have guessed, is to accurately recreate the configuration in which a real person's ears pick up sound. The subsequent recording is then intended to be listened to via headphones, resulting in an extremely accurate recreation of the original listening experience. Strangely enough, this technique has been perhaps most often used by individuals trying to illicitly record concerts by mounting tiny microphones near their ears. Those who have experienced such records are often quite impressed with the resulting quality.
As mentioned earlier, the amateur has a lot to look forward to as he or she enters the world of recording. From microphones to mic placement to identifying and avoiding noise sources, there is a great deal that one must take into consideration in order to achieve the highest possible quality in recording.
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Last modified 4/26/97.