Does My Mix Work in Mono? Phase Correlation & Stereo Width

Your mix works in mono if the left and right channels stay in agreement when they're summed together — nothing important cancels out. Phone speakers, most Bluetooth boxes, and club subwoofers all collapse stereo to a single mono sum, and anything out of phase (usually the bass) thins out or disappears. A phase-correlation meter tells you before you ever hear it: near +1 is mono-safe, near 0 loses energy, below 0 actively cancels. You can check any track free in TrackGleam's mono compatibility checker and stereo field meter — measured in your browser, nothing uploaded.

Why does mono still matter in 2026?

Because a huge share of real listening is mono, and it isn't going away. A single phone speaker plays one channel — a mono sum of your left and right. Most Bluetooth boxes have one driver. Laptop speakers, a lot of smart speakers, and club and festival subwoofers all collapse stereo to mono, either because there's one speaker or because bass is routed to a single sub. Even a stereo Bluetooth pair standing a few feet apart in a noisy room behaves close to mono for anyone not sitting in the sweet spot.

So "it sounds great in my headphones" tells you almost nothing about how it lands where people actually hear it. A mix that's wide and enormous on studio monitors can arrive on a phone with the kick gone and the bassline thin — not because the phone is bad, but because the phone exposed a phase problem your headphones were hiding. Checking mono compatibility isn't a nice-to-have; it's checking the format most of your audience is on.

What is phase correlation, and what do +1, 0, and -1 mean?

Phase correlation is a single number that describes how similar your left and right channels are. It runs from +1 to -1:

• +1 — the two channels are identical. The track is effectively mono, and it survives a mono sum untouched.
• Around 0 — a wide, spacious stereo image. Still fine, but summing to mono will lose some energy.
• Below 0 — the channels are fighting each other. When a system sums them, the out-of-phase parts cancel and disappear.

For the full mix, most engineers aim for roughly +0.5 to +1. The number that matters most, though, is the low band below about 150 Hz — bass and kick belong centered and in phase, so you want the low band sitting close to +1. A whole-mix correlation can look acceptable while the bass alone is dipping negative, which is exactly the case that kills your low end in mono. That's why a good meter reports low-band and high-band correlation separately.

What actually kills mono compatibility?

Mono problems almost always come from pushing stereo width where it doesn't belong. The usual culprits:

• Out-of-phase stereo — anything that inverts or delays one channel against the other (a mis-wired stereo effect, an aggressive mid/side move) drives correlation negative and cancels on sum.
• Stereo wideners on the whole mix — widener plugins create width by making the sides out of phase. Feels huge in headphones, then collapses on a phone. Widening the low end is the single most common cause of a bass that "disappears" in mono.
• Wide reverb and stereo delays — long, super-wide reverb tails and ping-pong delays carry a lot of anti-phase side energy. Fine up top; dangerous if they're smearing into the low mids.
• Hard-panned or widened bass — bass and kick pushed off-center, or run through a stereo enhancer, partly cancel the instant left and right are added together.

The pattern is consistent: width down low is the trap. Width up top — cymbals, pads, air, reverb tails — is where stereo lives safely, because those elements aren't carrying the weight of the track and a little cancellation there isn't fatal.

How do I check if my mix works in mono?

Two free tools, no upload, both measuring in your browser with the Web Audio API — so they work on unreleased demos and private stems:

The mono compatibility checker gives you a phase-correlation reading for the overall mix and — more importantly — for the low band below ~150 Hz, flags how much of the track spends time out of phase, and then lets you hear it. Hit its Mono button and it sums left and right in real time so you can A/B against stereo and judge exactly how much low end you'd lose on a phone. That audible A/B is the honest test: the meter warns you, the sum proves it.

The stereo field meter is the wider view — it reports overall correlation, stereo width as a percentage, and low-band (20–150 Hz) versus high-band (2–8 kHz) correlation side by side. Reading those two bands separately is what tells you whether your width is safe width (up top) or risky width (down low). If the low band drops toward or below zero, that's your kick or bassline getting ready to vanish.

A quick manual version costs nothing too: flip your master bus to mono and listen. If the bass, kick, or a wide synth gets noticeably quieter or drops out, you've found the problem — the meters just tell you where it is and how bad.

How do I fix a mix that falls apart in mono?

Three moves, roughly in order of impact:

• Mono the low end. Collapse everything below ~120–150 Hz to mono (a mono-maker or elliptical filter, or just pull back any widening on bass and kick). This alone fixes the majority of "bass disappears on my phone" cases, because it forces the low band back toward +1 correlation.
• Tame the widener. If a stereo widener is on the master or on a bass-heavy element, back it off or remove it. Get your width from arrangement and genuine stereo sources up top, not from a plugin faking it by pushing the sides out of phase.
• Check correlation, then re-check the sum. Watch the low-band number climb back toward +1, then flip to mono one more time and confirm the bass holds. Trust the mono sum, not just the meter.

This is also exactly what a good master does automatically. TrackGleam's free mastering keeps the low end centered and mono-safe while preserving the width up top, and it measures the finished file rather than trusting a setting. No hype here: mastering won't invent stereo width you didn't record, and it can't rescue a mix that's badly out of phase everywhere — that's a mix fix, not a master fix. But for the common case — a widener overcooked the lows — mono-ing the bottom is a real, verifiable fix, and it's free to check either way.

Master a track free — mono-safe low end, nothing uploads