Balance in mastering means two things: tonal balance - how energy is spread across the frequency spectrum - and stereo balance - the relationship between what sits in the centre and what sits at the sides. EQ and mid/side processing are the tools for both.
Mastering EQ is subtle
In mastering you are EQing the whole mix at once. Every move affects every instrument.
- Broad strokes. Wide, gentle curves - often 0.5 to 2 dB - rather than narrow surgical cuts. A small shelf moves the whole character of a record.
- Cut first. Reductive EQ - removing rumble, taming a low-mid build-up, softening harshness - usually comes before any boosts.
- Boost gently. Additive EQ, often with analogue-style equalisers, adds air, warmth or presence.
- Listen at matched loudness. A boost makes things louder, which sounds better. Compensate for level before judging.
Linear-phase and minimum-phase
- Minimum-phase EQ - like most analogue and standard digital EQs - shifts phase around the frequencies it changes. This is part of the character of many classic EQs.
- Linear-phase EQ avoids phase shift, so it changes tone without smearing transients or affecting the stereo image - useful for mid/side work and steep filtering. The trade-offs are latency and pre-ringing on very steep or low-frequency moves.
Choose by ear.
Matching a reference
Compare your premaster's spectrum with your reference's at matched loudness. Look for broad differences - too much 200-400 Hz, not enough air above 10 kHz, a sub that is weaker or stronger - and correct them gently. Matching EQ plug-ins can suggest a curve; treat it as a starting point, never a final answer.
What mid/side is
Stereo audio is usually thought of as left and right. Mid/side describes the same signal differently:
- Mid = left + right - everything common to both channels: usually the kick, bass, snare and lead vocal.
- Side = left - right - everything that differs between the channels: reverbs, wide synths, doubled guitars, stereo effects.
Mid/side began as a microphone technique, pairing a forward-facing microphone with a sideways figure-of-eight microphone, developed by EMI engineer Alan Blumlein in the 1930s. It was also used in cutting vinyl, where excess low-frequency side content could make the stylus jump out of the groove. Today, mid/side processing lets you process the centre and the sides of a finished mix separately.
Mid/side in practice
- Mono the low end. Cut low frequencies from the side channel (below roughly 100-150 Hz) so the bass and kick are centred and solid - essential for clubs and vinyl.
- Widen the top. A gentle high shelf on the sides adds width and air without changing the centre.
- Clarify the centre. A small presence boost on the mid can bring a vocal forward; a small cut can tuck it back.
- Mid/side compression. Compressing the mid controls the core elements without squashing the stereo ambience; compressing the sides tames overly wide or busy effects.
- Width control. Adjust the side level to make the whole mix wider or narrower.
Monitoring mid/side
Solo the mid and side channels while you work. Listening to the side channel alone shows exactly what is wide in the mix - including problems such as phasey effects or out-of-phase bass.
Always check in mono. Width created by boosting the side channel can disappear or turn hollow on mono systems, which include many phone speakers, smart speakers and club systems.
Do this now
- Compare your premaster's spectrum with a reference at matched loudness and note the three biggest differences.
- Correct them with broad EQ moves of no more than 2 dB.
- Solo the side channel of your premaster and listen. High-pass the sides below 120 Hz and compare in mono.
- Add a gentle high shelf to the sides only and judge whether the width improves the master.
Builds on the lesson notes of J.M. Brooklyn Audio Mastering, with thanks.