How to Check Mono Compatibility in Your Mix

Here is how to check mono compatibility: sum your mix’s left and right channels to mono, measure how much level and detail you lose, and look at the phase correlation over the whole song to find sections that go out of phase. The free stereo width and phase checker does all three in your browser: drop in a bounce and it shows correlation, mono collapse loss, side-to-mid balance and a correlation graph, with a Mono switch so you can hear the result.

Why mono compatibility matters

A lot of real-world playback is mono or close to it: phone speakers, many Bluetooth speakers, some club and venue systems, and any situation where the listener is far from a stereo pair. When left and right are added together, any part that is out of phase between the channels partly cancels. Wide synths can shrink, reverb can vanish and, in the worst cases, the bass or a lead part almost disappears. A mix that sounds huge on headphones can fall apart on a phone if you never check it.

Key terms

Term	What it means
Phase correlation	How similar left and right are, from +1 (identical, mono) through 0 (unrelated) to −1 (opposite polarity).
Mono collapse loss	How much quieter the mix gets when summed to mono.
Mid	What left and right have in common (L + R).
Side	The difference between left and right (L − R): the stereo information.
Stereo width	How much side there is relative to mid.

For the theory behind cancellation, see our explainer on phase cancellation.

Step 1: Bounce the mix

Export a stereo bounce of the full mix or master, at the same sample rate and bit depth as your project. Check the whole song rather than a loop, because phase problems often appear only in one section, such as a wide chorus or a breakdown with a stereo pad.

Step 2: Load it into the phase checker

Open the stereo and phase checker and drop in the file. It is decoded with your browser’s built-in audio decoder and analysed on your device; nothing is uploaded or stored.

Step 3: Read the overall numbers

• Phase correlation. Most finished mixes sit roughly between +0.3 and +0.9. Readings near 0 mean very wide or uncorrelated material. Anything below 0 means parts of the mix will cancel in mono.
• Mono collapse loss. A mono signal loses 0 dB when summed. A hard-panned or fully uncorrelated signal loses about 3 dB. A polarity-inverted channel can disappear completely. A small loss is normal; a large one tells you a lot of the mix lives in the sides.
• Side-to-mid balance and width. Side close to or above mid means a very wide mix, which is more likely to change in mono.

Step 4: Find the problem sections on the graph

The correlation graph runs across the whole song. Look for dips toward or below zero and note the time. Then jump to that point and listen. Common culprits:

• a stereo widener or chorus on a synth or pad;
• a double-tracked guitar or vocal where one take is polarity-flipped;
• a stereo-recorded instrument with mics at different distances;
• stereo reverb or a wide delay that dominates a breakdown;
• a bass or 808 processed with a stereo effect.

Step 5: Listen in mono

Press play and switch Mono on. Numbers tell you where to look; your ears tell you whether it matters. Listen for:

• the vocal or lead getting louder relative to everything else (a sign the backing is wide);
• a part that drops away or turns thin and hollow;
• bass and kick losing weight;
• reverb tails disappearing.

Some change is expected. The goal is that every important part stays audible and the balance still works.

Step 6: Fix and re-check

1. Check polarity on double-tracked or multi-miked parts. Flip one side and keep whichever sounds fuller in mono.
2. Keep kick and bass mono. Low frequencies carry the most energy and are the most damaging when they cancel.
3. Reduce widener amounts on pads and synths, or apply them only above the low mids.
4. Use mid/side EQ to narrow low frequencies in the side channel on wide buses.
5. Re-bounce and re-check. Compare correlation and collapse loss with the first pass.

Worked example

A pop mix reads +0.6 overall, but the graph dips below zero during each chorus. In mono, the chorus synth pad almost vanishes. The pad uses a stereo chorus effect with a wide setting. Halving the chorus width and high-passing the pad’s side channel below a few hundred hertz brings the chorus correlation back above zero, and in mono the pad now stays audible while the stereo version still sounds wide.

Should you mix in mono?

Some engineers balance levels and EQ in mono first, because masking is easier to hear when everything shares one position. Others mix in stereo and check mono at milestones. Either works, as long as you check. Our article on mixing in mono weighs the pros and cons.

Check stems and buses, not just the mix

When the full mix shows a problem but you cannot hear which part causes it, bounce the suspect buses on their own: drums, music, vocals and effects returns. Run each one through the checker. A drum bus with room mics often reads lower correlation than you expect, and an effects return with a wide reverb can read close to zero on its own. That is fine for a return, as long as the dry parts underneath stay solid in mono. Narrowing down to one bus is usually faster than muting tracks one at a time.

When a wide reading is fine

Not every low or fluctuating reading is a fault. Ambient intros, reverb tails, stereo room recordings and sound-design transitions are meant to be wide, and short dips during those moments rarely hurt the listener. What matters is that the parts carrying the song, such as the vocal, the bass, the kick, the snare and the main hook, stay strong in mono. If those survive the mono switch and the overall correlation stays positive, a little width in the background is a creative choice rather than a problem.

Common mistakes

• Checking only a loop. Phase problems are often section-specific.
• Chasing +1 correlation. A fully mono mix is safe but loses the width you want. Aim for a positive, stable reading.
• Widening the low end. Stereo bass is one of the most common causes of mono collapse.
• Ignoring polarity on doubles. One flipped mic can hollow out a whole part.
• Judging only by numbers. Always listen in mono as well.

FAQ

For more balance and stereo technique, read our mixing guide and the background on phase in waves. Before you send your next bounce out, run it through the free stereo and phase checker.