# Mono compatibility check
Source: https://docs.aden.space/docs/help/make-music/mono-compatibility

Phase analysis per track version: what the mix loses when a club, phone or radio chain sums it to mono.
{/* Generated by `bun docs:publish` from docs/features/mono-compatibility.md: edit the spec, not this file. */}

## What it is [#what-it-is]

Most places your song gets played sum the stereo image to mono: club systems,
phone speakers, most Bluetooth boxes, a lot of radio and TV chains. Anything
sitting out of phase between left and right disappears in that sum. A wide
synth thins out, a phase-flipped bass cancels itself, an overwide master loses
several dB of level, and none of it is audible on headphones.

The mono check listens to a version and tells you what survives that sum:

* **Correlation**, from +1 (both channels the same) through 0 (very wide) to
  -1 (the channels cancel each other).
* **Mono level drop**, how much level the mono sum loses against the stereo
  file. More than about 1.5 dB is worth a look, 3 dB is a problem.
* **Stereo width**, how much of the mix lives in the side signal.
* **Per band**, the same correlation split into low (under 250 Hz), mid and
  high, because wide air up top is fine while wide bass is not.
* **Correlation over time**, so you can see the section where it goes wrong
  instead of guessing, with a timestamp for the worst moment.

Then you listen to it. Play the version and flip the player between **Stereo**
and **Mono** while it runs, so the numbers turn into something you can hear.
"Jump to" drops you straight onto the worst moment in mono.

## Using it [#using-it]

1. Open **Tracks → a track → Versions**, play the version, and click the LUFS
   readout above the waveform to open the equalizer panel. Mono compatibility
   sits under the EQ, next to the Stereo/Mono switch it drives.
2. Press **Run mono check** at the bottom of the block. The audio is analyzed in
   your browser, so it takes a few seconds on a long master. The verdict, the
   correlation meter and the Stereo/Mono switch are what you get back; the per
   band numbers, the level drop, the width and the correlation timeline sit
   behind **Details**.
3. Play the version and switch between **Stereo** and **Mono**. The same switch
   sits in the player's equalizer panel (opened from the LUFS readout), next to
   pitch and speed, so you can flip to mono on anything that is playing.
   That A/B is the point: the meter tells you how much collapses, your ears
   tell you whether it matters.
4. Read the verdict badge:
   * **Sums cleanly**: nothing to do.
   * **Wide, still sums**: pull back the stereo widener on the master.
   * **Thins in mono**: something under 250 Hz is off center. Center the bass.
   * **Cancels in mono**: a channel is polarity flipped. Check the stems.
5. Fix it in your DAW, upload the new version, run the check again.

The result is kept with the version only once you have actually listened to it
in mono. Run the check, walk away, and nothing is stored.

Versions that thin or cancel in mono also carry a badge in the versions list,
so a problem master is visible before anyone opens it.