Mid/Side Processing: The Sound Engineer's Guide to Stereo Imaging
Invented in 1934 by British acoustic engineer Alan Blumlein for stereo microphone recording, Mid/Side (M/S) processing is one of the most powerful techniques in mixing, mastering, and modern audio restoration.
The Mid/Side Matrix Algorithm
$$\text{Mid} = \frac{L + R}{2} \qquad \text{Side} = \frac{L - R}{2}$$
$$\text{Left} = \text{Mid} + \text{Side} \qquad \text{Right} = \text{Mid} - \text{Side}$$
Forward and inverse Mid/Side matrix transformations
Practical Applications in Audio Mastering
- Mono-Compatible Bass Tightening: Bass frequencies below 100 Hz can be cut from the Side channel using an elliptic high-pass filter, focusing all low-end punch into the center Mid channel for vinyl cutting and subwoofers.
- High-Frequency Stereo Widening: Applying a high-shelf boost on the Side channel expands the perception of air and spatial ambiance without altering the vocal presence in the Mid channel.
- Karaoke Vocal Removal: Attenuating the Mid channel extracts stereo instrumentals by canceling identical center-channel vocal phases.
Experience real-time M/S matrix processing with the Studio LOOS Vocal Remover & Karaoke Extractor.
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