Audio Glossary
Stereo · aka mono fold-down, phase coherence
WHAT IS
MONO COMPATIBILITY?
Mono compatibility means a mix still sounds right when its left and right channels are summed to a single channel. Club systems, phone speakers, and many Bluetooth devices play essentially in mono, so a mix that collapses in mono (vanishing leads, hollow drops) fails on exactly the systems dance music lives on.
Why stereo tricks disappear in mono
When left and right sum, any content that is out of phase between the channels cancels. Wideners, stereo delays, and haas-effect tricks create width precisely by decorrelating the channels, which is why the widest-sounding elements are the first casualties of the fold-down. The synth that felt huge in headphones is the one missing from the club PA.
This is physics, not a quality setting: the more width you buy with phase, the more you owe when the system sums. Width created with level and arrangement (double-tracking, panning real sources) survives; width created with phase alone does not.
How I check and protect it
The check costs one button: put a utility plugin on the master, flip to mono, and play the drop and the chorus. If nothing important changes level dramatically, you are safe. If a lead or the low end vanishes, find the phase-heavy element and rein it in. I do this after every width adjustment while mastering, no exceptions.
The standing rules on my own releases: everything below ~120 Hz stays mono (club subs are mono anyway), widen above that only when the mix earns it, and never widen with an element the song cannot afford to lose. A mid/side-capable chain makes the low-end rule a one-switch job.
Quick answers
MONO COMPATIBILITY FAQ.
Do phones and Bluetooth speakers really play in mono?
Many effectively do: single-driver phone speakers and small Bluetooth units sum the channels, and even stereo phone speakers sit so close together that heavy side content mostly cancels or vanishes. A large share of real-world listening is closer to mono than to headphones.
Should the low end always be mono?
Below roughly 120 Hz, yes, for dance music. Club systems sum lows to mono, stereo bass wastes limiter headroom, and phase-y low end turns to mush on big systems. Mono lows are the cheapest professional upgrade a master can get.
Does mono compatibility still matter on streaming?
More than ever. Streaming means your record plays on whatever device is nearby, and the nearby device is usually a phone or a small speaker. The mix that survives mono is the mix that survives real life.
Related terms
The tool for it
Ultimate Master Chain Bundle
Five chains. Every mastering sound — analog color, transparent precision, console character. The exact builds on 50M+ streams.
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