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Mini-MP – User's Guide

APOGEE ELECTRONICS

MS Recording and Playback

Introduction

When recording with a stereo microphone array, the engineer has a wide variety of microphone placement

schemes at his disposal, each with specific strengths and weaknesses. One placement may ensure mono

compatibility of the recording but result in a rather narrow stereo image, while another placement may create a

spacious stereo image but result in phase cancellations and comb filtering when the recording is played in mono.

The MS Recording technique, consisting of the MS Microphone Array and the MS Decoding Matrix, offers

adjustable stereo image width and perfect mono compatibility. It's even possible to adjust stereo width after the

recording has been completed, or re-adjust the width of an existing stereo program when mastering.

As mono reproduction is still quite common in the broadcast, film and video worlds, MS techniques are widely

used in these productions. MS techniques can also prove useful in any situation where a stereo mic array might

be used, such as piano, drum overhead or ensemble recording.

The MS Microphone Array

The MS Microphone Array consists of two identical variable pattern microphones, one set to the cardioid pattern

and the second set to the figure 8 pattern. The cardioid mic is positioned so its capsule directly faces the sound

source, while the figure 8 mic is positioned so its capsule is at a 90 degree angle to the sound source and as

close to the cardioid capsule as possible. The cardioid mic is connected to the Mini-MP's Left input, while the

figure 8 mic is connected to the Right input.

MS Microphone Array

MS Polar Patterns in relation

to the sound source

The MS Decoding Matrix

In order to obtain a standard Left – Right stereo signal from an MS Mic Array, the two inputs described above

must pass through a decoding matrix in the Mini-MP. Indeed, if one were to listen to the MS Mic Array without

decoding, one would hear a direct signal on the left side, a diffuse signal on the right, and pretty much no precise

stereo image. Instead, the cardioid (or Mid) signal is routed to both the Left and Right channels equally and in

phase, while the figure 8 (or Side) signal is routed to both channels equally but with a 180 degree phase reversal

on the Right channel. A more advanced analysis of the Decoding Matrix is presented below in the "Advanced

Techniques" section of this manual

Using MS Mode on the Mini-MP

When the Mini-MP's POWER switch is set to MS, the inputs are configured to accept an MS Microphone Array,

the Decoding Matrix described above is applied to the two signals, and a standard Left-Right Stereo signal

is routed to the outputs. The stereo width of the Left-Right output may be adjusted by modifying the balance

between the LEFT / MID and RIGHT / SIDE controls. To better hear the characteristic of the Mid and Side

components of the Left-Right output, decrease the RIGHT / SIDE control to minimum, leaving the center mono

Mid signal; next decrease the LEFT / MID control to leave only the "phasey" unstable Side signal. In practice, a 3

to 1 ratio of Mid to Side signal is considered an appropriate point of departure.