Mono vs. stereo (mono compatibility)

Mono is one channel of audio, played identically everywhere. Stereo is two channels carrying slightly different content, which is what creates left, right, and width. Mono compatibility is the question of whether your stereo mix still sounds correct after a device sums those two channels back into one.

Speech should almost always be mono. A voiceover recorded on one mic and exported as 'stereo' is just the same signal twice: double the file size, zero benefit, and one more chance for a channel to go missing. Keep stereo for music, ambience, and anything with real spatial content. Podcasts commonly ship mono, video usually ships stereo with dialogue centered.

The failure mode is phase cancellation. If the two channels contain near-identical content with a small delay or flipped polarity, summing them subtracts instead of adds, and parts of the mix get quieter or vanish. Plenty of current phones and Bluetooth speakers do play real stereo, but mono playback and downmixing are still everywhere: single-speaker phones and smart speakers, laptop drivers an inch apart, most venue and PA installs, one earbud in, and the force-mono accessibility setting. So the mono check is not optional. Also watch the one-sided export: audio recorded to the left channel only, which plays in one earbud and sounds like the file is broken.