Mid-Side (M/S)
Definition
A stereo processing technique that separates a stereo signal into its center content (mid) and stereo width content (side), allowing independent processing of each component. Widely used in mastering and mixing for precise stereo control.
In Simple Terms
A technique that separates the center of your stereo mix from the sides. It lets you brighten or widen just the sides without touching the vocal in the middle, or vice versa. Powerful in mastering.
In Practice
M/S EQ in mastering applies a high-shelf boost only to the mid channel, adding air to lead vocals and centered instruments without affecting the width of cymbals and room sound in the side channel.
Common Confusion
M/S processing does not "create" stereo width — it lets you sculpt the width that already exists. If a mix is mostly mono, M/S has nothing to widen on the side channel. Engineers sometimes reach for M/S as a fix for a narrow mix, only to discover that the source content itself is the actual problem.
Sources & Verification
- Blumlein, A. D. — UK Patent GB394325: Improvements in and relating to Sound-transmission, Sound-recording and Sound-reproducing systems1933
- Streicher, R. & Dooley, W. — Basic Stereo Microphone PerspectivesJournal of the Audio Engineering Society, 1985
- Eargle, J. — The Microphone Book (2nd ed., chapters on M/S technique)Focal Press, 2004
Last verified: 2026-05-05