The hook
After the service, three people describe the same problem three ways. The pastor's wife says his mic sounded "like he was in a barrel." The drummer says the vocal was "muddy." A visiting musician says there was "too much low-mid." They all heard the same thing: a pile-up around 300 Hz that one EQ knob could have removed.
You've kept the EQ flat since Level 0, and that was right. Flat until you know what you're fixing. Now you're ready, because EQ only makes sense once you can hear a problem and name where it lives. This lesson gives you both halves: what the knobs actually do, and the map that turns "barrel" into "300 Hz."
The lesson
From lesson 1.1: every sound is a stack of frequencies, lows through highs all sounding at once. A voice isn't "at" one pitch; it has a fundamental around 100–250 Hz, body above that, consonants up at 2–4 kHz, breath and air higher still.
That's the entire concept. Everything else is knowing the tools and knowing the map.
The tools
Every EQ you'll meet is built from four filter shapes.
High-pass and low-pass filters. The cliff edges. A high-pass removes everything below its frequency (you've been using it since 3.5); a low-pass removes everything above. They don't boost. They only clear away.
Shelves. A gentle ramp that raises or lowers everything beyond a point: a high shelf at 8 kHz tilts the whole top end up or down; a low shelf does the same for the bottom. The HIGH and LOW knobs on an analog board's EQ are shelves. Broad, forgiving tone controls.
Bells (peaking filters). The precision tool: a bump or dip centered on one frequency. A fully parametric bell gives you three controls: which frequency, how much boost or cut (gain), and how wide the bell is (Q). Low Q is a wide, musical curve that touches octaves of material; high Q is a narrow surgical notch that touches almost nothing but its target. Digital console EQs are parametric, and the rest of Level 4 lives on this filter.
Graphic EQs. A row of small faders, each a fixed-frequency bell — typically 31 of them, a third of an octave apart. No frequency or Q to choose; just grab the 315 Hz fader and pull. Fast and coarse. You'll usually find one on monitor and main outputs, not channels. It comes back in 4.4.
The map
Naming the tools is the easy half. The map is the real skill: knowing where sounds and problems live on the 20 Hz–20 kHz line. Here's the working geography:
| Zone | What lives there | When there's too much | When there's too little | |---|---|---|---| | 20–80 Hz | Sub-bass: kick weight, bass bottom | Rumble, mud you feel | No foundation | | 80–250 Hz | Body: warmth of voices and instruments | Boomy, thick | Thin, cold | | 250–500 Hz | Low mids: fullness | Muddy, boxy, "barrel" | Hollow, scooped | | 500 Hz–2 kHz | Midrange: where instruments crowd | Honky, nasal | Distant, vague | | 2–6 kHz | Presence: consonants, attack, edge | Harsh, fatiguing | Dull, buried | | 6–12 kHz | Air: sparkle, breath, cymbal shimmer | Sibilant, brittle | Dark, closed |
Read the middle column again. Those words are the translation dictionary. "He sounded like he was in a barrel" is 250–500 Hz. "It's harsh, my ears are tired" is 2–6 kHz. "The vocal is muddy" — 250–500 again. Congregation complaints arrive in adjectives; the map converts them to frequencies; the EQ does the rest.
Two landmarks to pin the map with. Presence, 2–6 kHz, is where intelligibility lives: the consonants that make words words (the territory the vocal was fighting for in 3.5). And the low mids, 250–500 Hz, are where live mixes go to die: every instrument on stage puts energy there, it stacks up channel after channel, and the result is the most common ailment in church audio. The next two lessons are basically "how to manage the bottom half of the map."
Go deeperoptional
Q, precisely. Q is the filter's center frequency divided by its bandwidth between the −3 dB points of the bell: Q = f₀/BW. A bell at 1 kHz with Q = 1.4 spans roughly one octave (about 707 Hz to 1.41 kHz); Q = 4 covers about a third of an octave; Q = 10 is a sliver, the feedback-notching regime of 4.4. Some console EQs display bandwidth in octaves instead of Q; same information, inverted. One subtlety between brands: with proportional-Q designs the bell sharpens as you boost or cut harder, while constant-Q designs hold the width regardless of gain. Worth knowing which yours does when a gentle 2 dB cut and an aggressive 8 dB cut behave like different filters.
Every EQ move is also a phase move. The analog and standard digital EQs you'll use live are minimum-phase filters: changing the magnitude response necessarily shifts the timing of frequencies around the bell (the phase response is mathematically tied to the magnitude, the Hilbert transform relation). For one channel alone this is inaudible and harmless. It starts to matter when correlated signals sum: EQ one of two mics on the same source differently from the other, and the phase shift moves which frequencies reinforce and cancel between them (the 3.1 polarity lesson's subtler cousin). Studio-world linear-phase EQs avoid this by paying with latency and pre-ringing, a trade live sound almost never makes. The DSP mechanics (biquad filters, coefficients, the z-plane) live in Level 9.4.
Why the map's zones aren't arbitrary. The ear analyzes sound in critical bands — roughly third-octave-wide analysis channels along the cochlea (9.3 covers the Bark scale properly). Energy landing within one band blends and masks; energy in separate bands stays distinguishable. The map's zones approximate runs of adjacent critical bands with shared perceptual character, and the third-octave spacing of graphic EQs isn't a coincidence; it's engineering matched to cochlear resolution. Masking is also frequency-asymmetric: strong energy masks upward, toward higher frequencies, more than downward. That single fact drives the next lesson's rule: controlling an instrument's low-mid pile-up clears more audible space above it than boosting the masked material ever will.
"Flat" is a convention about electronics, not sound. A channel EQ at zero means the console adds no shaping. It says nothing about the mic (a Shure SM58's presence peak of several dB around 4–5 kHz is EQ by transducer design, from 2.4), the speaker's response, or the room's. The chain is never flat; the EQ's zero is just the point where you stop adding opinions to the opinions already present. That reframe matters in Level 6, where you'll meet system EQ (equalizing the PA itself against a measured room), and it's why "EQ flat" was always a starting point, not a claim of neutrality.
Remember
- EQ is frequency-selective volume: more or less of a chosen slice, the rest untouched.
- Four tools: high/low-pass (cliffs), shelves (ramps), bells with frequency/gain/Q (precision), graphics (31 fixed bells).
- The map: 20–80 sub, 80–250 body, 250–500 mud, 500–2k crowding, 2–6k presence and intelligibility, 6–12k air.
- Complaints arrive as adjectives: barrel, muddy, harsh, thin. The map converts them to frequencies.
- EQ comes third: after gain is clean (2.2) and balance is right (3.5). It shapes; it doesn't rescue.
Your turn
- Find the EQ section on your board and identify each band: which are shelves, which are bells, and which knob is Q.
- Do the sweep drill for ten minutes: +10 dB bell, sweep 100 Hz to 8 kHz over familiar music, name the zones out loud.
- Translate three complaints you've actually heard at church into zones on the map.
- Check whether your board's high and low bands can switch between shelf and bell. Many can, and it changes what they're for.