Mono Compatibility
Mono compatibility means your mix sounds good when all stereo information is collapsed to a single channel. Critical for club playback and phone speakers, poor mono compatibility can cause bass frequencies to cancel out or wide elements to disappear entirely when summed to mono.
Phase cancellation is the enemy of mono compatibility. When two signals that are identical but out of phase are summed, they cancel each other out—the result is silence or a severely thinned sound. Excessive stereo widening using phase-based techniques can introduce this problem.
To check mono compatibility: use a Mono button on your master bus (available in most DAWs and monitoring controllers) and compare the full stereo mix to the mono version. Elements that disappear or change character dramatically indicate phase problems.
Common causes of mono incompatibility include: over-wide mid-side processing, certain chorus and flanger effects that work by phase shifting, stereo delays where left and right sides are out of sync, and some sample-based supersaw presets with extreme unison spread. Fixing typically involves reducing the side signal level or adjusting phase alignment.