Samson MTR231 Manual Del Propieratio página 10

Stereo Microphone Techniques
The term "stereo" will be used here to describe different microphone techniques
using multiple channels of audio to create a reproduction of the sound stage over
a pair of loudspeakers. There are many approaches that can be used with two or
more microphones, but we will focus on three methods: spaced microphones, X/Y
coincident pairs and Mid-Side (MS).
Spaced Microphones - This technique utilizes two microphone placed 2-10 feet
apart (sometimes a third microphone is used in the center). Traditionally, engi-
neers have chosen omnidirectional microphones for this method which have a flat
polar and frequency response, but include more of the reverberant sound of the
room compared to the direct signal. This approach works well for smaller perfor-
mance groups, such as chamber music, where specific imaging of instruments on
the stereo plane is not crucial. The closer the two microphone are arranged, the
wider the stereo image appears. The figure-8 pattern can be used for this tech-
nique but in this case, the microphones need to be angled in the direction of the
sound source. Cardioid microphones are usually avoided due to the degradation of
its off-axis frequency response.
X/Y Coincident Pairs - This technique uses two cardioid microphones placed as
close as possible together with a splayed angle of 90°-135°. The closer the angle
between the microphones is to 90°, the more narrow, or mono, the soundstage
will appear. Since cardioid pickup patterns tend not to reproduce signals off-axis,
the result is a drier, more direct sound recording. A variation of the X/Y pairs,
is the Blumlein configuration which utilizes two crossed figure-8 patterns. This
technique can also be used as a variation to the Mid-Side method below. Using
this approach produces a more natural sound, because the polar and off-axis
frequency response is much better than the cardioid pattern, it captures more of
the room's reverberant sound. The disadvantage using two figure-8 microphones
is that they will pick up sounds coming from behind the microphones, which may
not be desirable.
Mid-Side (MS) - The MS configuration might be the most versatile and power-
ful technique of the three discussed. This arrangement typically uses a forward
facing cardioid microphone for the "mid" portion, which is recorded equally to
the left and right channels, and a side facing figure-8 microphone for the "side"
component which is recorded to the left and right channel (with one of the chan-
nel's polarity reversed). The MS method has the best stereo-to-mono compatibility,
because when the two channels are summed to mono, the side microphone is
completely cancelled. The width of the stereo field can be made wider or more
narrow by adjusting the level of the "side" component relative to the "mid" com-
ponent.
10