Frequency, Hearing, and Three Charts Worth Keeping
Turning knobs and trusting your ears is how most of us learn EQ, and there's nothing wrong with that. You develop instincts that way. But at some point, having a framework underneath those instincts makes them sharper. You start hearing why something works, not just that it works.
This post covers three ideas about frequency and hearing that are worth understanding early. None of them are complicated. Each one comes with a reference chart you can keep open while you work.
1. Frequency Has a Vocabulary
When someone says a mix sounds "boxy," they're talking about roughly 300–800 Hz. "Nasal" points to the 1–3 kHz zone. "Muddy" lives around 100–300 Hz. "Air" is up past 10 kHz.
These aren't standardized terms, different engineers use them slightly differently, and the exact frequencies shift depending on the instrument. But the general map is consistent enough to be useful as a shared language.
Roey Izhaki's Mixing Audio includes a chart that organizes these terms by what you hear when there's too much of a frequency range (excess), what you associate with it at normal levels, and what it sounds like when it's missing(deficiency). It's one of the most practical reference charts in any mixing book.
You don't need to memorize it. Just start connecting words to ranges. Once "harsh" means 4–8 kHz to you instead of just a feeling, you can act on it faster.
As Izhaki explains:
“We use these terms in verbal communication, but we might also use them in our heads—first, we decide that we want to add spark and then we translate it to a specific frequency range.”
Source: Izhaki, Roey. Mixing Audio: Concepts, Practices, and Tools (p. 230). (Function). Kindle Edition. Subjective terms we associate with various frequency ranges, and what excess or
deficiency sounds like in each range.
These terms are not standardized and the frequency ranges are rough.
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Click here to download this chart in print quality!
2. Your Ears Aren't Flat
Our hearing responds differently to different frequencies, and the response changes depending on how loud the signal is.
The equal-loudness contours (often called Fletcher-Munson curves) map this out. At low listening volumes, we hear midrange frequencies, particularly around 3–4 kHz, where our ears are most sensitive, much more prominently than lows and highs. The bass and top end get rolled off by our own hearing. As you turn it up, the curve gets flatter.
This has important relevance for mixing:
If you're working at low volumes, you're hearing a version of your mix with less low end and less high end than what's actually there.
That's useful to know. And not because low-volume mixing is wrong, but because you can account for it instead of chasing a problem that's perceptual, not musical.
Equal Loudness Contours
How loud something sounds depends on its frequency. Our ears are not flat — they boost some ranges and bury others, and the curve changes depending on volume.
Based on ISO 226:2003 equal-loudness contours. Curves are simplified representations — actual contours are more detailed at specific frequencies.
3. Instruments Don't Stay in One Lane
Every sound has a frequency range where its fundamental energy is. A kick drum lives between about 40 and 200 Hz. Vocals run from roughly 80 to 500 Hz. Hi-hats are mostly above 1 kHz.
But fundamentals are only part of the picture. A kick has low-end weight, but its attack shows up around 2–5 kHz. A vocal has body in the low-mids, presence around 2–4 kHz, and sibilance near 6–10 kHz. A synth bass might have its root at 60 Hz with harmonics and grit stretching past 1 kHz, which puts it in the same zone as an electric bass. In practice, their ranges overlap heavily. The distinction is more about sound design than physics.
This is why frequency conflicts between instruments aren't always where you'd expect. A kick and bass clashing might not be a sub problem at all — it could be their harmonics colliding around 200–400 Hz, as well. A vocal that feels buried might not need more volume; a synth pad might just be occupying the same midrange space.
Knowing where things live including their fundamentals and harmonics, turns EQ from guesswork into decision-making.
Where Instruments Live
Approximate frequency ranges for common instruments and elements in electronic and popular music. Solid bars show fundamentals, faded bars show harmonics and overtones.
Ranges are approximate and vary by patch, tuning, and processing. In practice, synth bass and electric bass overlap significantly — the separation here is stylistic, not physical. FX elements like noise and risers are almost always filtered in context. Hover bars for details.
Theory into Practice
These aren't advanced tricks, but the architectural fundamentals of audio. Grasping them ensures that your tools remain subordinate to your taste, allowing you to make intentional decisions rather than throwing plugins at a problem.
We explore the practical application of these concepts deeply within the Soft Synced ecosystem.
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