Stereo & Phase Meter — Check Mono Compatibility Online, Free

height = stereo width green = in-phase red = anti-phase (collapses in mono)

This file is mono — there's no stereo width or phase to show.

now —

Mono compatibility —

Stereo width —

How to read the band: height = stereo width, colour = phase. A flat green line is mono; a tall green band is wide and in phase (both safe in mono); a tall red band 🚩 is out of phase and cancels when the track is summed to mono.

Table of Contents

One band instead of three instruments
What "phase" and "correlation" mean
Why mono compatibility still matters
The round goniometer and the live needle
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Frequently Asked Questions

One band instead of three instruments

A studio stereo meter is really three readouts you have to learn: a round goniometer, a moving correlation needle, and somewhere a width meter. This tool folds the two that matter onto a single band you read at a glance:

Height = stereo width. A flat line in the middle means the signal is mono. The taller the band, the more the left and right channels differ — the wider it sounds.
Colour = phase. Green means the channels are in phase (they add up). Red means they’re out of phase (they cancel). Yellow is the in-between.
Brightness = loudness, so quiet passages fade out instead of painting misleading colour.

The band runs along time, so you don’t just get a verdict — you see which second of the track has the problem. Click it to jump there, and a flag marks each spot worth re-checking.

A plain-English verdict sits above it — mono-safe, watch, or phase risk — for the whole track, with a live now reading that follows the playhead as it plays. Width is reported separately, as neutral character (mono · narrow · balanced · wide), never as a fault: a narrow mix isn’t wrong — only anti-phase is.

What "phase" and "correlation" mean

Stereo is two signals: left and right. Correlation measures how alike they are, from +1 to −1:

+1 — left and right are identical. That’s mono: it sums perfectly, nothing is lost.
0 — the channels are unrelated. Wide and lush, and still safe.
−1 — right is the inverse of left. Added together they cancel to silence.

Real anti-phase usually comes from an over-eager stereo widener, a mis-wired or phase-flipped mic pair, or a sample with the effect baked in. The band turns red exactly where it happens.

Why mono compatibility still matters

Your monitors are stereo; a lot of the world is not. Phone speakers, most Bluetooth speakers, club subwoofers, a laptop, a TV across the room, many social-media players — they collapse left + right to mono. Whatever sits in anti-phase there doesn’t just narrow; it disappears. A bassline or a lead that’s huge on headphones can vanish on a phone. This meter is the 10-second check that it won’t — and when you want to be sure, the Mono toggle folds playback to a mono sum so you can hear exactly what collapses.

The round goniometer and the live needle

The round goniometer is the live “now” panel. Aim for the dashed oval: a cloud that stands up is in phase and mono-safe; a cloud lying on its side is out of phase and cancels when the track is summed to mono.

While a track plays, the right-hand panel shows the classic instruments for "right now": the round goniometer (a vertical cloud = mono/in-phase, a cloud lying on its side = anti-phase) and a live correlation needle sweeping −1 to +1. They’re there if you grew up on a hardware meter — but the band is the part you actually read.

Nothing leaves your browser

The file you drop is decoded and analysed locally with the Web Audio API. It is never uploaded, never stored, never sent anywhere. Close the tab and it’s gone.

Frequently Asked Questions

What does a stereo / phase meter do?

It shows how the left and right channels of your track relate: how wide the stereo image is and whether the channels are in phase. That tells you whether the track will survive being played in mono — on phones, Bluetooth speakers, club subs and many social players — without parts cancelling out.

What is mono compatibility and why should I care?

A huge share of listening happens in mono (one speaker, or left+right summed). Anything that sits out of phase cancels when the channels are summed, so a bass or lead that sounds huge on headphones can disappear on a phone. Checking mono compatibility before you release catches that.

What does the correlation number mean?

It runs from +1 (channels identical — pure mono, sums perfectly) through 0 (unrelated — wide but safe) to −1 (right is the inverse of left — they cancel to silence in mono). Below about 0 for sustained stretches is a warning.

Is a goniometer the same thing?

Yes — a goniometer (or vectorscope) is the round dot-cloud display of the same data. A vertical cloud = mono/in-phase; a cloud lying on its side = anti-phase. This tool shows the goniometer for the playhead, but lays the important parts out over time as a band so you can see where a problem is, not just that one exists.

Do I need to upload my file?

No. The audio is decoded and analysed entirely in your browser with the Web Audio API. Nothing is uploaded or stored — close the tab and it's gone.

What audio formats can I load?

Anything your browser can decode — WAV, MP3, M4A/AAC, FLAC, OGG. For the most accurate phase reading, use a lossless file (WAV or FLAC); heavy MP3 encoding can slightly alter the stereo image.

My file shows a flat green line — is it broken?

No — that means the file is mono (or both channels are identical). There's no stereo width or phase difference to display, which is itself perfectly mono-compatible.

How do I fix an out-of-phase (red) section?

Find the source: back off a stereo widener, check for a phase-flipped or mis-wired mic pair, or replace a sample that has the effect baked in. Re-check until the band stays green where it counts.

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