Home › What is stereo correlation?
Stereo correlation is a single number from +1 to -1 describing how alike your left and right channels are. At +1 they are identical (mono); at 0, unrelated; at -1, opposite — and opposite signals cancel to silence the moment playback is mono. Which is more often than you think.
Values near +1 mean a centered, mono-solid image. A mix hovering between +0.5 and +0.9 is wide but healthy. Sustained readings near 0 mean the sides dominate — impressive on headphones, fragile everywhere else. Negative correlation means energy that will actively cancel in mono: what was a huge synth becomes a hole in the mix on a phone speaker, a club PA summed to mono, or a Bluetooth speaker.
Correlation is also frequency-dependent, and the low band is where it has physical consequences.
Mono playback is the everyday reason: phones, smart speakers, most club systems below the crossover. Vinyl is the unforgiving one — out-of-phase bass translates to vertical stylus motion, and past a limit the cut becomes unplayable. That's why cutting engineers check low-frequency correlation specifically, and why vinyl pre-mastering narrows the image below roughly 100–300 Hz with elliptical EQ.
The reliable recipe is width where hearing localizes poorly and coherence where energy lives: keep bass and lead vocals essentially mono, push width in reverbs, pads and doubled parts above the low mids, and check the mix summed to mono at every stage. Widener plugins that work by phase inversion buy their width with exactly the correlation you can't afford — measure before trusting them. The mid/side ratio (how much energy sits in the center versus the sides, in dB) is the companion number worth watching.
The vinyl check measures low-frequency correlation against real cutting limits — the same physics, on your file.
Check my master's phase — freeSustained readings above roughly +0.5 with dips during wide moments are typical of healthy masters. Sustained values near or below 0 predict mono problems worth checking by ear.
Classic low-correlation symptom. Headphones present the side signal fully; speakers in a room — and any mono summing — collapse it. Check correlation and listen in mono.
Yes, mechanically. The stereo difference cuts vertically into the groove; too much low-frequency difference and the stylus loses contact or the groove depth becomes uncuttable. Plants will reject or mono your lows for you.
Find the source: phase-inverted widening, hard-panned bass-heavy elements, or stereo effects on the low end. Mono the lows (elliptical EQ or a mid/side filter), replace inversion-based wideners, and re-measure.
Why vinyl needs its own master, and what changes.
Your master vs real cutting limits — free report.
The loudness unit behind every platform's normalization.