← Gazillion Industries/Reading material

Fletcher-Munson curves

Gazillion Industries · September 20, 2026

The mix sounded perfect last night at volume. This morning at conversation level the bass has vanished and the vocal is shouting. Your monitors did not change. Your ears did, and they do it every single time.

The Fletcher-Munson curves, published in 1933 and since refined into an international standard as the equal-loudness contours, describe how human hearing changes with level. We are most sensitive in the upper midrange, roughly two to five kilohertz, and considerably less sensitive at the extremes. That imbalance gets worse as things get quieter: at low volume the bass and the top disappear faster than the middle does. Which means every mix decision you make is tied to the volume you made it at.

The short version

Why loud always sounds better

Turn any record up and the curve flattens: the low end and the air arrive in proportion, and the whole thing sounds bigger and more exciting. That is not the record improving. It is your hearing becoming more even.

This is the mechanism behind the oldest trap in audio, which is that the louder of two things wins the comparison regardless of which is better. It is why level-matching before an A/B is not a nicety but the entire validity of the test, and it is why a mastering engineer turning your mix up by two decibels can appear to have improved it enormously.

What to do about it

1. Pick one moderate monitoring level and do your balance decisions there, every session.
2. Use the volume knob as a test, not as a mood: turn up briefly to check the low end, turn down to check the balance.
3. Make the important decisions quietly. A balance that works at low volume almost always works loud; the reverse is not true.
4. Check on something small and horrible as well, because a phone speaker reproduces almost none of the range your ears are least sensitive to anyway.
5. Level-match every comparison you make, between plugins, between mixes, between your track and a reference.

BEEFY is a saturation and loudness effect, which makes it exactly the kind of plugin that flatters itself in an unmatched comparison. Match the levels before you decide it is working.

The part people get wrong

The curves are a description of hearing, not a prescription for mixing. They do not mean you should boost the bass to compensate, because your listener's ears have the same curves: if you correct for the effect, you have simply made a bass-heavy record that sounds wrong at the volume they actually play it at.

What they mean is narrower and more useful: pick a level, work at it, and know that any judgment you make at a different volume is being made by a different instrument.

Questions people ask

What is an equal-loudness curve?

A line on a chart showing which levels at different frequencies are perceived as equally loud. The original set was published by Fletcher and Munson in 1933 and later work refined it into the modern standard.

What frequency is the ear most sensitive to?

The upper midrange, broadly between two and five kilohertz, which is where speech intelligibility lives. That sensitivity is why a small boost there feels like a large one.

What volume should I mix at?

A consistent moderate level where you could hold a conversation, with occasional checks loud and very quiet. The exact number matters far less than using the same one every day.

Why does my mix sound different at different volumes?

Because your hearing's frequency response changes with level. At low volume you hear proportionally less bass and less top, so the same mix genuinely sounds different rather than merely quieter.

What BEEFY does

BEEFY is a saturation and loudness effect for making sounds thicker, punchier and more up front. It adds body, squeezes some space out of the peaks, and brings out harmonics that help a sound feel bigger — and those harmonics land in the range your ears are most sensitive to, which is precisely why saturating a bass line makes it audible on a speaker that cannot reproduce the bass note at all. BEEF, COOK and JUICE are the three knobs; SOFT CLIP and LIMIT are the output choices.

Your monitors are consistent. You are the variable, and you have been all along.

Keep reading

• Mono compatibility — Which kinds of width survive summing, and how to test for it.
• How to mix drums — Balance first, then EQ, compression, saturation and the bus.
• Why is my mix muddy? — Where mud lives in the spectrum, how to clear it, and what else causes it.

Gazillion Industries LLC · reading material