M S Techniques

MS techniques use one microphone, typically a cardioid, as its M or mid component and one bilateral (figure of eight) microphone as the S or side component. They are resolved into a conventional XY stereo signal by a sum and difference matrix network producing an M+S and M-S output. The left channel output is determined by the orientation of the positive lobe of the S component.

This system gained popularity due to its absolute mono compatibility, an important consideration during the mono to stereo transition era. This works because when you sum the left and right channels ((M+S) + (M-S) =2 M ) you are left with only the mid component. This also dramatically reduces the reverberant component as the side signals are nulled and the mid component is on axis with the centerline of the signal source. It is generally considered important to have less reverberant information in a mono signal than a stereo one.

The MS method also gives the recording engineer more control over the stereo image as the matrix output can derive any polar pattern between a tight hypercardioid and a wide cardioid pattern. This allows the engineer to control the amount of reverberant information, the width of the stereo image, and the apparent distance from the sound source. These adjustments can be made during the recording or, as we suggest, after the fact by recording the mid and side components separately.