Mid-Side Mastering
Processing mid and side separately lets width and low end be handled without undoing each other.
Related
Lift the side channel by 3 dB and the cymbals spread while the vocal steps back. Mid-side processing separates position, not level.
Encode and decode
Mid is half the sum of left and right; side is half the difference. Decoding adds and subtracts them back into left and right. Mono playback keeps only mid, so everything in the side disappears. A negative side reading means the channels are out of polarity and cancel when folded to mono. That property defines the limits of the technique: width placed in the side cannot be recovered in mono.
Four things to do separately
- High-pass the side below 120–200 Hz so the low end stays centred
- Cut a narrow band in the side to remove harsh upper mids
- Compress the mid gently to steady vocal and kick
- Lift the side a little, only above 2 kHz
- Leave the full band alone and widen the mids only
Working and listening
Fix balance in the mid first, then move to the side. Check mono after every change, and do not let the correlation meter sit negative for long. More than 2 dB of side lift hollows out the centre. Lifting low end in the mid is safer than cutting it in the side, since the mid cannot push content out of mono. With multiband mid-side work, inspect the crossover, since phase is fragile where the bands split. Match mid-side compression attack and release to the main chain, or the two sides breathe at different rates.
Where it breaks
If the mix itself has unstable phase, mid-side work magnifies it. A reverb that already fills the field becomes a tail over the vocal when widened further. Side lift after the limiter pushes peaks over the ceiling again. Uneven left and right levels put an offset in the side, which reads as a tilted image. Fix image problems in the mix; width is the last touch.
Listen in the library
All tracks from midicn-lib — inline badge is the license tier (C1 commercial / C2 non-commercial / C3 study only).
Along the same line
Sources
- Bob Katz, Mastering Audio.
- Brainworx, bx_digital V3 user manual, mid-side EQ behaviour.
- FabFilter, Pro-Q 4 user manual, mid/side processing mode.