EQ: Cutting, Boosting and Masking

An equaliser turns frequency ranges up or down. It's the most used and most overused tool in mixing. Good EQ is usually small, specific and done for a reason you can name.

The controls

• Frequency — the centre (or corner) of the band.
• Gain — how much to boost or cut, in dB.
• Q (bandwidth) — how wide the band is. Low Q (0.5–1) is broad and musical; high Q (5–10+) is narrow and surgical.
• Shape — bell, shelf (everything above or below a point), or filter (a steep roll-off).

Two rules of thumb hold up well: broad boosts, narrow cuts — a wide gentle boost sounds natural, a narrow boost sounds like a ringing resonance; and small moves — 2–3 dB is a real change. If you need 10 dB, the problem is probably the source, the arrangement or the balance.

Subtractive vs additive

Subtractive EQ removes something wrong: mud, boxiness, a ringing resonance, harshness. Do it early in the chain, before compression, so the compressor isn't reacting to the problem.

Additive EQ enhances something good: air on a vocal, weight on a kick. Do it after compression, where it shapes the final tone.

The classic way to find a problem frequency is to boost a narrow band and sweep it until the unpleasant thing jumps out, then cut there. Do this briefly — sweeping with a big boost for long fools your ears into hearing problems everywhere.

A frequency map

Range	Name	What lives there	Too much sounds
20–60 Hz	Sub	Kick and 808 fundamentals, sub bass	Rumbling, flabby
60–250 Hz	Bass	Bass body, kick punch, low of guitars and keys	Boomy
200–500 Hz	Low mids	Warmth and body of most instruments	Muddy, boxy
500 Hz–2 kHz	Mids	Character, honk, nasal tone	Honky, cheap
2–6 kHz	Upper mids	Presence, attack, intelligibility	Harsh, tiring
4–10 kHz	Presence / sibilance	Consonants, cymbals, string noise	Sibilant, brittle
10–20 kHz	Air	Sheen, breath, space	Hissy, thin

Mud (200–500 Hz) and harshness (2–6 kHz) are the two most common complaints, because nearly every instrument puts energy in those ranges, and it piles up.

High-pass filters

A high-pass filter removes everything below a frequency. Most sources other than the kick and bass have little useful content in the lowest octave, only rumble, handling noise and room. High-passing them keeps the low end clear for the parts that own it.

Set the filter by ear: raise it until the source starts to sound thin, then back it off. Typical results: vocals 80–120 Hz, guitars 80–100 Hz, pads and keys 100–200 Hz, hi-hats and cymbals 200–400 Hz or higher. Don't high-pass on autopilot — a pad or a piano can be what gives a sparse arrangement its warmth.

Masking

Masking is when one sound makes another harder to hear because they share a frequency range. Kick and bass fight in the low end; vocals and guitars fight in the mids.

Fixes, roughly in order of preference:

1. Decide who wins. In each range, one part should lead. The vocal usually wins the upper mids; the kick or the bass wins the sub.
2. Cut the loser where they overlap, a couple of dB. Better still, use a dynamic EQ on the loser, keyed from the winner: it cuts about 2 dB in the shared band only while the winner is playing, so the other part keeps its full tone the rest of the time.
3. Pan them apart, if neither has to be central.
4. Change the arrangement — a different octave or a different note is often the cleanest fix.

The old habit of carving a permanent hole in every instrument for the vocal tends to make parts sound hollow when soloed and the mix sound thin. Fix the overlaps that are actually a problem.

Overall tonal balance

Measurements of thousands of commercial releases show a consistent long-term shape: energy is highest in the low end and falls steadily through the mids, falling faster in the top octaves — records tend toward a shared target curve. A spectrum analyser with a 4.5 dB/octave tilt helps you spot a mix that's drifting too bright or too heavy. Set the actual amount of low end by comparing with references in your genre.