Mono compatibility check

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

1. Open Tracks → a track → Versions and open the version's … tab, next to BPM and key.
2. Press Run mono check. The audio is analyzed in your browser, so it takes a few seconds on a long master.
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.