Stereo Width & Mono Compatibility Checker

Knowledge Base

How to Read the Correlation Meter

The line graph shows phase correlation over the length of your file, from -1 (fully out of phase, will cancel in mono) through 0 (decorrelated, typical of wide reverb/stereo effects) to +1 (fully in phase, completely mono-safe). Most healthy mixes trend positive throughout, dipping only briefly and mildly negative on wide stereo moments like reverb tails.

What Counts as a Problem

Sustained correlation below about -0.3, especially on low frequencies or your most important elements (lead vocal, bass, kick), is worth investigating. It means real, audible cancellation is likely when this file is played back in mono. Brief, shallow dips on airy stereo effects are normal and not usually worth chasing.

Using the A/B Player

Switch to "Mono Fold-Down" and listen specifically for anything that thins out, gets quieter, or disappears compared to the stereo version. This is exactly what a phone speaker or smart speaker will do to your mix, so hearing it yourself here is the most direct way to judge whether it's actually a problem in practice.

FAQ

Q: My file shows negative correlation but sounds fine in mono, is that a problem?
A: Not necessarily, some deliberately wide effects (reverb tails, certain synths) naturally read negative on the meter without causing an audible problem when actually summed to mono. Trust your ears on the A/B player alongside the meter reading.

Q: Does this work on mono files?
A: A true mono file will show perfect +1 correlation by definition (identical signal on both channels). This tool is most useful for genuinely stereo material.

Why mono compatibility still matters

A large share of listening happens in mono. Phone speakers, most smart speakers, many laptops, and public address systems all sum the two channels together. If your mix falls apart when that happens, it falls apart for a substantial part of your audience, and they will not know why.

Phase correlation is the measurement to read. A reading near plus one means the two channels are closely related and will sum cleanly. Near zero means they are largely independent, which is normal for a wide mix and worth checking. Persistently negative means the channels are working against each other, and summing to mono will cancel content rather than combine it.

Cancellation removes rather than quietens. When a sound appears in both channels with opposite polarity, summing them produces silence at those frequencies. This is why a mix can sound impressively wide in stereo and lose its bass, or its lead vocal, entirely in mono. The wider the processing, the more there is to lose.

Keep the centre solid and widen around it. Bass, kick, snare and lead vocal are conventionally kept close to centre and largely mono, because those elements have to survive. Widening applies to material where losing some of it costs nothing, such as ambience, doubled guitars and reverb returns.

Check by listening rather than only by reading a number. Switching to mono and back is the fastest test available, and anything vanishing or thinning noticeably is a problem regardless of what the correlation meter says. Do it before delivery rather than after, since the fixes are simple in a session and impossible in a finished file.

Vocabulary

Phase correlation. A measure of how similar the two channels are, from plus one for identical to minus one for opposite. Predicts what happens when a mix is summed to mono, where negative values mean cancellation.

Mono fold-down. Summing the left and right channels into one. What phone speakers, many smart speakers and public address systems do automatically, and where phase problems become audible.

Side channel. The difference between the two channels, holding everything not common to both. Raising it widens a mix and increases what disappears in mono, since only the common part survives summing.

Cancellation. The reduction or removal that happens when two versions of a sound combine with opposite polarity. Not a reduction in volume but a removal of content, which is why it cannot be fixed by turning something up.