The ELPrinciple
Personal headphone calibration · both ears, equally loud — Six Walls
“The human ear does not perceive all frequencies as equally loud at the same physical intensity.” That’s the equal-loudness principle, and it’s where the name (and the little EL) comes from.
Your two ears don’t hear your headphones quite the same, either. Put a sound dead center and one side often wins, by a different amount at different pitches. The Principle measures that, for you on this pair of headphones, and evens it out on your monitor path, band by band. It only ever boosts the side that needs it, and nothing it does ends up in your mix.
For personal listening enjoyment only. This tool is not a medical device and does not diagnose, treat, or correct hearing loss. Results are not a substitute for a professional hearing evaluation. If you have concerns about your hearing, please consult a licensed audiologist or physician. (The full wording is at the end.)
It’s personal in the literal sense. Same headphones, different engineer: different calibration. Each person who mixes on a pair gives it a calibration of their own, under their own name.
Installing
Windows: run The-Principle-<version>-Windows-Setup.exe.
Click Yes on the one security prompt and it installs the VST3 to
C:\Program Files\Common Files\VST3\. If Pro Tools is
installed, tick Also install the AAX version for Pro Tools to add the
AAX to C:\Program Files\Common Files\Avid\Audio\Plug-Ins\.
macOS: open The-Principle-<version>-macOS.pkg. It
installs the VST3 and the Audio Unit (for Logic and GarageBand) for all users; a
Pro Tools (AAX) checkbox, off by default, adds the AAX. It is signed and
notarized by Apple, so it opens with no Gatekeeper warning.
Then restart your DAW or rescan plugins. Prefer to place the bundles yourself? The portable download holds the plugin bundles and a READ ME saying where each one goes. The Installer can also keep The Principle up to date for you.
Where it goes
On the monitor path, not the mix: the last thing before your headphones. In Studio One that’s the Listen bus; in other DAWs, a monitor or control-room insert, or the very end of the master bus.
- It bypasses itself when you render. In an offline bounce or export the audio passes through untouched, so a calibration left on the master bus can’t end up in the file. A real-time bounce looks like playback to the plugin, so turn it off by hand for those.
- Room or speaker emulation (Slate VSX and the like): put The Principle before it. Those plugins feed some of the left into the right to sound like speakers, which blurs a left/right adjustment. If you use VSX’s E.C.C.O. too, both are shaping the upper mids: try The Principle’s Amount lower before deciding which one you prefer.
Before you calibrate
- Headphones only. With speakers, both ears hear both speakers and a per-ear adjustment falls apart.
- Use the headphones you mix on. The calibration measures you and those headphones together, which is exactly what it needs. Switch headphones, pick (or make) that pair’s calibration.
- A quiet room. Fans, air purifiers, and air conditioning hide the low and middle bands.
- Nothing between The Principle and your ears. No room or headphone correction (Sonarworks and friends), no monitor EQ, no per-channel trims. If your interface feeds its headphone jacks through its own mixer (a PreSonus Quantum, for example), leave it centered, at unity, and with no EQ or processing.
- Set your mixing level, then leave the headphone volume alone. The wizard helps with this in step 2.
Calibrating: the wizard
Opening The Principle with no calibrations starts the wizard. After that, it’s New calibration… at the bottom of the headphones list, on the Manage page, or Recalibrate… on a calibration’s Details page. Six steps, about four minutes, plus about four more for the quiet run.
| Step | What happens |
|---|---|
| 1 Name | Name these headphones. Typing shows matching models from a built-in list of common mixing headphones (the arrow lists them all, by maker), and picking one fills in open-back or closed-back. Sharing headphones? Add your name, e.g. Beyerdynamic DT 990 Pro - Eddy. |
| 2 Level | Play pink noise (−20 dBFS RMS) or a loop of one of your own tracks, and set your headphone volume to where you mix. Pink noise sounds louder than most mixes, so err a little quiet; a track you know is closer to real life. Write down the Mixing Volume: the dB number or position your headphone output shows, so you can come back to it. |
| 3 How it works | The instructions and the Key (below). |
| 4 Center | Ten bands of noise, 250 Hz to 12.5 kHz, each played in both ears at once. Move each one until it sits dead center in your head. Each band comes up twice from a random start, and a third time if your two answers disagree by more than 6 dB. There is no slider and no number on screen, on purpose: people steer by where a thumb sits instead of listening. Rest your fingers on the arrow keys and close your eyes. |
| 5 Quiet | Recommended: the same thing 20 dB quieter, like the soft parts of a mix. It lets The Principle follow your ears at low levels too. Don’t touch the volume: the run turns itself down. Or Skip. |
| 6 Done | Says whether the pair is calibrated (the head turns green). |
Why centering? Off-center, a band seems to ping from one side to the other; evened out, it stays put in the middle of your head. That’s a much easier and finer call than “are these two equally loud?”, especially across different pitches.
The Key
| Key | Does |
|---|---|
| ← → | Move the sound left or right. |
| Enter | Lock it in and move on. |
| Backspace | Go back one. |
| L R | Only one ear hears it, however far you move it. That band gets the most boost Max Boost allows on the other side. |
| M | Both ears hear it, but it disappears toward the middle. You’re then asked which edge was louder (L, R, or S for about the same): the louder edge is the better ear. These answers have no size, so the weaker ear gets a cautious 6 dB. |
| N | No sound in either ear. That band gets no boost (your ears are the same there), and a later run that hears it replaces it. |
The Key on screen can be clicked, too. In a DAW, the keys can belong to the transport, so click the plugin window first.
The Listen page
| Control | Range | What it does |
|---|---|---|
| Headphones | your calibrations | Pick the headphones you’re mixing on. Each name is one calibration. The bottom of the list has New calibration… and Manage calibrations… |
| Boost right now | What it’s doing at this moment, per ear and per band. Peak sets how long the top LED holds: Fast (200 ms) or Slow (1 second). | |
| Amount | 0 … 150 % | How much of your calibration to apply. 100% is exactly the difference you centered, and the recommended setting. |
| Max boost | 0 … 20 dB | No band is boosted more than this. Default 12 dB. |
| Bypass | in / out | Crossfades, so A/B comparisons don’t click. |
| Safety Limiter | Boosts add level, so a limiter at −0.5 dBFS catches anything that would clip. The light shows when it’s working. | |
| Fit Check | See below. |
What the boost does
The weaker ear is brought up to the better one, band by band. Nothing is ever cut. With a quiet run in the calibration, the boost follows the music: each band of each ear has its own level detector, and loud passages get the amounts from your mixing-level run while quiet ones get the amounts from your quiet run, with a smooth slide in between. (Without a quiet run, quiet passages get the same amounts as loud ones.) Near silence it fades to nothing, so hiss and room noise aren’t lifted. In practice, the ringing and decay of a cymbal brighten in the weaker ear while the hit itself stays put.
Setting Amount by ear
Pan something bright hard to your weaker side and listen with The Principle on. Then bypass it, turn your headphones around (left cup on the right ear), and listen to the same thing in your better ear. Set Amount so the two sound alike.
Fit Check
Headphones sit a little differently every time you put them on, which mostly changes the top end (and the bass on closed-backs, through the seal). Fit Check tells you whether today’s fit matches the one you calibrated with. It needs a pair that has been calibrated at least once.
- Four sounds to center, one pass each: 1, 4, and 8 kHz, plus 250 Hz on closed-backs. Under a minute. Leave the headphone volume where you mix.
- Passed: kept as a light run (a quarter of the weight of a calibration), so over time the calibration learns how your fit varies.
- Off: nothing is saved. It tells you which band and which side, and asks you to reseat the headphones and check again. Off twice in a row: run a full calibration, since your ears or the pads may have changed.
Why doesn’t it just recalibrate? One quick pass is one seating plus the usual wobble in your answers. Rebuilding the EQ from it would chase noise.
Managing calibrations
One name, one calibration. Recalibrating a name replaces its old calibration; a new calibration under a name that’s taken asks before replacing it. To keep two, give them two names (Slate VSX and Slate VSX (loud), say).
Manage calibrations lists them all: the one in use is marked, with its type, when it was calibrated, and its Calibration Note. Each has Details:
- Headphones Name: click to rename, Enter saves. Plugins (or saved sessions) still set to the old name fall back to the most recent calibration.
- Open-back / Closed-back.
- Calibration Note: the Mixing Volume you wrote down. A note only: changing it doesn’t change the measurements.
- Notes: anything you like.
- View Graph: the calibration, drawn full size.
- Recalibrate… and Delete…
Calibrations are small files in %APPDATA%\Six Walls\The Principle\profiles
(~/Library/Application Support/Six Walls/The Principle/profiles on
macOS). Uninstalling The Principle leaves them where they are.
A very different listening level on the same pair wants its own calibration under its own name. The levels in a calibration are relative to the headphone volume you set in step 2.
Is it the headphones, or me?
A lean to one side can come from you or from the headphones. To tell them apart, wear the headphones backwards (left cup on the right ear) and calibrate again under a new name, e.g. DT 900 Pro X (reversed). Never reuse the real pair’s name: that would replace its calibration.
- The numbers belong to the cups, not your ears: “left” always means the left cup.
- If the lean flips to the other cup, it’s the headphones. If it stays with the same ear, it’s you. Usually it’s some of each.
- Either way, the normal calibration is right for wearing them the right way round: evening out the pair is part of the job. Delete the reversed one afterwards so nobody picks it by mistake.
The reversed test can’t tell the cups from anything upstream that follows the channel: the interface, its mixer, a headphone amp, a monitor EQ. That’s why it pays to calibrate with nothing in between. A pair that’s off by a lot can be a worn pad, a pad that doesn’t seal the same way (glasses, hair), or a tired driver. Swapping the pads side to side is a quick check.
The toolbar
The bar along the bottom is the same on every Six Walls plugin: undo and redo, A/B comparison, the zoom steps, the version number, and the ? button, which opens this manual and About The Principle.
Known limitations
- It only finds differences between your ears. Anything both ears share doesn’t show up in a centering calibration.
- It’s tied to your headphone volume. The levels are relative to the volume you set in step 2. Mix at the same setting.
- Neighboring bands overlap a little. Each band’s level detector hears its own third of an octave, so a quiet band next to a loud one is judged on its own.
- Your answers wobble a bit, like anyone’s. Small boosts of 2 to 3 dB can be noise as much as ears. Passed Fit Checks add to the calibration over time and settle it down.
Not a medical device or hearing aid
This application is designed solely to personalize your listening experience by measuring your personal frequency response and generating a custom EQ profile for your headphones. It is not intended to diagnose, treat, cure, or mitigate any medical condition, including hearing loss, hearing impairment, tinnitus, or any auditory disorder.
Results generated by this application reflect your subjective listening preferences under specific test conditions and should not be interpreted as a clinical audiogram or a measure of auditory health. This application is not a substitute for professional hearing care. If you are concerned about your hearing, please seek evaluation from a qualified audiologist or hearing healthcare professional.
Credits & licenses
The version number is shown in the plugin’s bottom toolbar; the ? button there opens this manual and the About box.
- JUCE 8 — built with JUCE (juce.com) under the free JUCE Personal license; the “Made with JUCE” splash on the editor is part of that license.
- Fonts — Orbitron, Rajdhani, IBM Plex Mono, and Atkinson Hyperlegible, under the SIL Open Font License 1.1. The full license texts are under Third-party licenses in the About box.