EQ (Equalisation)

EQ is the most-used processor in audio, and for good reason. Every sound you hear is made up of frequencies — low rumble, midrange body, high-end sparkle — and EQ lets you turn each of those frequencies up or down independently.

That's it. No magic, no mystery. It's a volume knob that only affects the frequencies you point it at.

Key Info

What EQ Actually Does

Every sound — a voice, a guitar, a kick drum — is made up of dozens or hundreds of individual frequencies sounding simultaneously. Those frequencies determine the tone. A bright vocal has strong high frequencies. A boomy kick has too much energy in the low end.

EQ gives you surgical control over this. You pick a frequency, decide whether to boost or cut it, and set how wide the adjustment should be. That's the whole concept. Everything else is just detail.

Filter Types Explained

High-pass (Low-cut)

Removes everything below a set frequency. Set it to 80 Hz on a vocal and you kill the rumble, air conditioning hum, and proximity effect buildup without touching anything useful. This is the single most underused EQ move in amateur mixes. Nearly every track in a session benefits from a high-pass filter — the only question is where you set it.

Low-pass (High-cut)

The opposite. Removes everything above a set frequency. Useful for taming harsh cymbals, pulling hiss out of noisy recordings, or pushing a sound further back in the mix. A gentle low-pass on a rhythm guitar at 8–10 kHz keeps it out of the vocal's territory without making it sound dull.

Bell / Peak

The workhorse. Boosts or cuts a specific band of frequencies centred around a chosen point. The width of the band is controlled by the Q parameter — a high Q value gives you a narrow, precise adjustment; a low Q gives you a broad, gentle curve.

Use narrow bells for surgical problem-solving (notching out a resonance). Use wide bells for tonal shaping (adding warmth, presence, or air).

Shelf

Boosts or cuts everything above or below a set frequency. A high shelf at 10 kHz adds air and openness to a vocal. A low shelf at 200 Hz adds weight to a thin-sounding bass guitar. Shelves are your go-to for broad tonal adjustments — they sound natural because they affect a wide range evenly.

Notch

A very narrow, deep cut designed to remove a specific problem frequency. Resonant room modes, mains hum at 50 Hz, feedback frequencies — these are notch territory. You're not shaping tone here; you're performing surgery.

Subtractive vs Additive EQ

Here's a principle that will improve your mixes immediately: cut first, boost second.

When something sounds dull, your instinct is to boost the highs. But often the problem is too much low-mid energy masking the high end. Cut the mud at 300–400 Hz and the brightness you wanted is already there — you just couldn't hear it.

Subtractive EQ is cleaner. Boosting adds energy to the signal, which can cause clipping, introduce phase issues, and generally make things sound worse faster. Cutting removes energy, which gives you more headroom and a cleaner mix.

The practical rule: cut narrow, boost wide. Narrow cuts are surgical and precise. Wide boosts are gentle and musical. A 12 dB narrow boost at 3 kHz sounds aggressive and unnatural. A 2 dB wide boost across the same region sounds present and polished.

Frequency Spectrum Quick Reference

| Range | Frequency | Character | |-------|-----------|-----------| | Sub bass | 20–60 Hz | Felt more than heard. Kick drum thump, bass weight. Too much and the mix falls apart on small speakers. | | Bass | 60–250 Hz | Warmth and body. Fundamental frequencies of bass guitar, lower vocals. Mud lives here if unchecked. | | Low mids | 250–500 Hz | Boxiness and warmth. The "cardboard" quality of badly recorded vocals sits around 300–400 Hz. | | Mids | 500 Hz–2 kHz | The meat of most instruments. Intelligibility of vocals. Cut here and things sound hollow; boost here and things sound nasal. | | Upper mids | 2–4 kHz | Presence, edge, and bite. This is where vocals cut through a mix. Also where harshness lives if overdone. | | Presence | 4–8 kHz | Clarity, definition, consonants. Sibilance becomes a problem around 5–8 kHz. | | Brilliance / Air | 8–20 kHz | Shimmer, sparkle, air. Cymbals, breath, the sense of space. Most people over 30 can't hear much above 16 kHz. |

Interactive frequency chart →

Common Mistakes

EQ-ing solo instead of in context. A vocal might sound thin on its own but sit perfectly in the mix. Always EQ with the rest of the session playing. The only exception is when you're hunting for a specific resonance — solo the track, find the problem frequency, then switch back to the full mix before deciding how much to cut.

Boosting when cutting elsewhere would work. If the vocal needs more presence, try cutting the guitars at 2–4 kHz first. You'll get the same result with a cleaner mix.

Too many narrow boosts. Multiple narrow boosts create a spiky, unnatural frequency response. If you find yourself stacking five or six narrow boosts, step back and ask whether you've got a recording problem rather than a mixing problem.

Ignoring the high-pass filter. Low-frequency energy you can't even hear on your monitors is eating your headroom and making your compressors work harder. Put a high-pass on everything that isn't a kick drum or bass, and your mixes will immediately sound tighter.

Plugin Recommendations

Further Reading

• FabFilter Pro-Q 4 Official Page
• TDR Nova Official Page
• Sound On Sound — Understanding EQ