Stereo Width, Panning and Mono Compatibility in 2026

The mix is enormous in your headphones. Then you play it through one Bluetooth speaker in the kitchen and something has gone missing. The vocal is further away, the guitars have thinned out, the whole thing feels quieter at the same volume. Nothing is broken in the session. What happened is that the width was doing more work than you realised, and a single speaker just took it away.

This is the guide to the part of mixing that decides whether that happens: how the stereo image actually works, what panning is really for, why some width survives mono and some evaporates, and the twelve specific failures that show up in real mixes. Each one gets the same treatment — what it sounds like, why it happens, the measurement that confirms it, and the fix.

There is a genuine disagreement to resolve first, because the advice on this subject contradicts itself more than on any other mixing topic. One camp says mixing in mono is the secret to everything. Another says it is a waste of time that costs you the stereo picture. One says your mix needs more width; another says wide mixes need less width. All four positions have something right in them, and the section that settles it is roughly halfway down.

Where hard data exists I have used it instead of my impressions. RoEx analysed 7 million tracks through Mix Check Studio and found mono compatibility problems in 17 percent of mixes and phase problems in 16 percent — and critically, those rates barely improve in the mastered versions, which means most of these problems are never caught by anyone at any stage. Mix Analytic report the counterpoint from their own analysed mixes: catastrophic stereo failure is rarer than its reputation, and the more common miss is playing it so safe the mix stays narrow. Both findings are useful, and together they say the same thing. Check mono so you know you have not broken anything, not because width is dangerous.

For the record, this is written by YECK, founder of MixingGPT. MixingGPT measures stereo correlation and left/right balance as part of its audio analysis, and there is a section near the end explaining exactly what it reports, how it scores it, what it costs, and the one thing it structurally cannot do on this topic. Everything before that section is tool-agnostic: every failure here is diagnosable with a free correlation meter and a phone.

Quick Reference: All 12 Stereo Failures at a Glance

If you want the 30-second version, find your symptom in the middle column and check what the right-hand one tells you to measure. The full read on each is below.

Failures 1 to 5 destroy information and are worth fixing before anything else. Failures 6 to 12 waste an opportunity or misplace it, which is a different and less urgent kind of wrong. Number 11 has no clean measurement attached and I have said so rather than inventing one.

What You Are Actually Controlling

Most stereo confusion comes from treating width as a single knob. It is not. There are four separate things happening, they fail in different ways, and mixing them up is why widener plugins get blamed for problems that panning caused.

• Position. Where a source sits between the speakers, set by the level difference between left and right. This is panning, and it is the only one of the four that is essentially free. Nothing cancels.
• Width. How far a source spreads rather than where its centre is. This requires genuinely different content in the two channels, and how you create that difference determines whether it survives being summed.
• Correlation. How similar the two channels are, which is what actually determines mono behaviour. This is the one you can measure, and the one most people never look at.
• Depth. How far forward or back something sits, built from level, early reflections, reverb amount and high-frequency loss. Depth is not width, and confusing the two is failure 11 below. There is a full technique breakdown in Jaycen Joshua’s front-to-back panner.

The mid/side identity that explains everything else

One piece of arithmetic makes the rest of this article obvious. A stereo signal can be described as a mid component, which is what the two channels share, and a side component, which is what they do not. Mono fold-down adds left and right together. When you do that, the mid content sums and the side content cancels completely — not partly, exactly.

That single fact is the whole story. The side channel is, by definition, the part of your mix that does not survive mono. So the question is never “is width dangerous?” It is “how much of my width lives in the side channel, and can I afford to lose that much?” Width from two genuinely different performances panned apart mostly survives, because those are unrelated signals that simply get relatively quieter when summed. Width from processing one mono source into a fake stereo pair does not survive, because the difference between the channels is the effect.

How to read a correlation meter

A phase correlation meter is the most useful and least used tool in this part of mixing. Every major DAW ships one and the free ones are fine. Sound on Sound’s explainer and Apple’s documentation for the Logic correlation meter both describe the same scale.

Two habits make the meter genuinely useful rather than decorative. First, watch it across an entire playthrough instead of one bar — correlation moves with the arrangement, and the section that dips is almost always the section with the problem. Second, put one on individual channels and buses, not only the master. A master reading of +0.5 tells you the mix is fine on average, which is not the same as no element being broken.

1. The Mix Loses Level or Elements When Folded to Mono

This is the umbrella symptom. Failures 2 through 5 are its specific causes, but it earns its own entry because this is how you will actually encounter it: not as a diagnosis, but as the moment a mix you were happy with sounds wrong somewhere else.

What it sounds like: wide and impressive on monitors or headphones, then hollow, thin, or oddly quiet on a phone, a single Bluetooth speaker, a laptop, a smart speaker, or a club PA. Often the first thing you notice is not the width at all but the balance — the vocal seems further back, or one part has stepped behind everything else.

Why it matters more than it used to: the number of genuinely mono playback endpoints has gone up, not down. A phone on a table. A single smart speaker. A Bluetooth speaker. A laptop with drivers two inches apart. Broadcast. A DJ booth monitor. A club sub array. None of those are edge cases and none of them are going away.

What to measure: the actual level change when you fold to mono. Put a utility plugin on the master, note the loudness, engage mono, note it again. A small dip is normal and expected. A large drop is a real problem. Separately, listen for which element changed, because that identifies the culprit faster than any meter — if the vocal doubles vanish, the problem is in the doubles.

The fix: do not fix it on the master. A mono problem on the master is always a mono problem on a specific channel, and correcting it with a global width reduction throws away the width that was working in order to hide the width that was not. Fold to mono, solo your way to the source, then fix it there. The rest of this article is about which sources those tend to be.

2. Fake Width: A Widener Plugin on a Mono Source

The most common single cause, and the one that feels most like progress at the time. You have a mono synth or a mono guitar, it sounds small, you put a widener on it, and it instantly sounds bigger. Nothing about that experience warns you.

Why it happens: there is no width in a mono file to reveal. A plugin cannot uncover stereo information that was never recorded, so it has to manufacture a difference between the channels — usually with a short delay, an all-pass network, a polarity inversion on one side, or a mid/side boost. Every one of those works by making left and right disagree, and mono fold-down is the operation that deletes disagreement.

The tell: engage the plugin with a correlation meter open. If the reading drops hard toward zero or below on a source that was previously mono, the width is entirely side content and mono will take all of it. In the worst cases the summed result is thinner than the original mono file, which means the plugin made the mix worse on a phone in exchange for sounding better on headphones.

The fix, in order of preference: record or program a second take and pan the two apart, which is real width and costs nothing in mono. Failing that, use micro-pitch detuning rather than delay-based widening. Failing that, band-limit the widening so it only applies above the mids, where cancellation costs least. Use a full-range widener on a mono source as a deliberate effect, not as a default.

For vocals specifically this is a solved problem with a far better toolkit — real doubles, ADT, micro-pitch and mid/side — and it has its own guide in how to get wide vocals. The modulation options are compared in best modulation plugins.

3. Haas and Short-Delay Width That Comb Filters

The Haas trick — duplicate a mono source, delay one copy by a few milliseconds, pan the pair apart — is genuinely useful and also the most predictable way to wreck a mono fold-down. It earns its own entry because the mechanism is arithmetic, which means you can work out in advance exactly what it will do.

Why it widens: below roughly 30 to 40 milliseconds the ear fuses the two arrivals into one sound rather than hearing an echo, and pulls the apparent direction toward whichever arrived first. That is the precedence effect, and it is why a 15 ms delay reads as space rather than as a slap.

Why it breaks: when you sum a signal with a delayed copy of itself, the two cancel at every frequency where the delay equals half a wavelength and reinforce where it equals a full one. That is a comb filter. For a delay of t seconds the first null lands at 1/(2t) and the notches then repeat every 1/t. So the shorter the delay, the further apart the notches sit:

The honest read: there is no delay time that is mono-safe. Short delays give you fewer, wider notches, which is a tonal change you can live with. Longer ones give you dense combing, which is the metallic sound people describe as “phasey.” Neither is free. If a Haas widener is sitting on a part you need intact on a phone speaker, the technique is wrong for that part.

The fix: use it on parts you can afford to lose — pads, ambience, background layers, effect returns — and keep it off the lead vocal, kick, snare and bass. Two better options for parts that must survive: micro-pitch detuning, where the cancellation moves continuously instead of parking on fixed frequencies, and simply recording the part twice.

4. Stereo Content Below 120 Hz

The most expensive width in a mix and the least audible. Stereo low end costs you punch, costs you translation, costs you a clean vinyl cut, and buys almost nothing — because the ear cannot localise it in the first place.

Why there is nothing to gain: localisation relies on differences in arrival time and level between your two ears, and those differences scale with frequency. A 50 Hz wave is roughly 6.9 metres long. A human head is about 0.17 metres wide. There is no meaningful difference for the ear to work with, which is why a subwoofer can sit anywhere in a room and why cinema formats have always summed the low-frequency channel.

Why there is plenty to lose: when out-of-phase low frequency sums to mono it cancels, and that cancellation lands precisely on the region carrying weight and punch. On vinyl the consequences are physical rather than perceptual: out-of-phase low content drives the cutting stylus vertically instead of laterally, which is what elliptical EQ exists to prevent. And club systems overwhelmingly run their subs summed, so stereo sub content in a club is a gamble with no upside.

What to measure: correlation on the low band specifically, not the master. Solo everything below roughly 120 Hz and check the reading holds near the top of the scale. Mix Analytic’s data suggests most producers already get this right, so a clean reading here is likely — but it is a one-button check on the one thing that is genuinely non-negotiable.

The fix: collapse everything below roughly 100 to 120 Hz to mono with a mid/side or elliptical EQ, and set the crossover by ear rather than by rule — a sparse track with a melodic bassline can go lower, a dense one benefits from going higher. Then decide which element owns the sub, because monoing the low end does not resolve two sources fighting over it. That part is covered in the nine causes of kick-and-bass low-end conflict, how to mix bass in 2026 and four advanced kick-and-808 sidechain tricks.

5. Phase and Polarity Between Doubles and Multi-Miked Sources

Worth separating two words that get used interchangeably and are not the same thing. Polarity is a straight inversion — the waveform flipped upside down, equally at every frequency, fixed with a polarity button. Phase is a time relationship, which is frequency-dependent, and no polarity button fixes it because the misalignment is different at every frequency. Flipping polarity on a time-misaligned source does not correct it, it just changes which frequencies cancel.

What it sounds like: the giveaway is counterintuitive. Two layers sound thinner together than either sounds alone. You mute one and the remaining one gets fuller. If muting something makes the mix bigger, you are looking at cancellation rather than a balance problem.

Where it comes from: a snare top and bottom mic pointing at opposite faces of the same drum, which is the textbook case for a polarity flip. A kick in and out mic. Overheads and close mics at different distances from the same source. A DI blended with an amp. Two vocal doubles derived from the same take with an offset. Multi-miked acoustic guitar, which is why mixing acoustic guitar gets its own workflow. And samples layered under recorded drums, which almost never align by default.

The diagnostic that settles it: solo the pair, flip polarity on one, and keep whichever sounds fuller. That takes two seconds and catches the polarity cases outright. For time misalignment, nudge one layer in samples while listening to the low end, or use the null test — flip one layer and listen to what is left. A deep null means the two are near-identical and one of them is redundant. A loud residual means they are genuinely different and safe to layer.

The part almost nobody checks: EQ shifts phase. Every minimum-phase filter — which is most EQs on most settings — introduces a frequency-dependent delay around the band it is working on. Two layers that summed perfectly can start cancelling after you EQ one of them. If a layered source gets thinner as you EQ it rather than brighter, re-check the polarity relationship after the EQ, not just before. Phase behaviour by plugin is compared in best EQ plugins in 2026.

Why this one survives into releases: RoEx found phase problems in 16 percent of mixes and essentially the same rate in mastered files. Mastering cannot fix it, because by then the cancelling layers are already summed into one file and the information is gone. This is a problem that only exists in the session and can only be solved there.

6. The Mix Is Too Narrow (The More Common Failure)

Everything above is about width that breaks. This one is about width you never used, and according to the measurement data it is more likely to be your actual problem. Mix Analytic report that across their analysed mixes correlation stays positive, bass stays centred, and almost nothing loses real level in mono, while only a small share push into genuinely wide territory. The scary failure is rare. The timid one is common.

What it sounds like: small. Congested. Every part occupying the same spot, so the arrangement feels busier than it is and each element has to fight for level instead of for space. It reads as a masking or EQ problem, which is why people spend hours carving frequencies on a mix that needed panning.

Why it happens: a decade of well-intentioned mono-compatibility advice taught a generation to treat width as a hazard. Add the fact that a narrow mix never fails a mono check and you get a stable, safe, unremarkable result that nothing in your workflow flags as wrong.

What to measure: correlation sitting at or very near +1 on a full, dense arrangement means there is no stereo development to speak of. Worth stating plainly, because this gets treated as a pass: a mix reading +0.99 has not won the mono test, it has declined to take it.

The fix: pan with intent rather than in small increments. Give every part a decided position, then widen the supporting layers — doubles, pads, percussion, ambience, effect returns — while the core stays centred. The rule Mix Analytic use for this is the right one: anchor the core, widen the support.

7. Hard-Panned Parts That Lose 6 dB in Mono

Not a cancellation problem, a level problem, and it catches people out because nothing sounds broken — the balance simply changes.

The arithmetic: a centred element exists in both channels, so when they sum it reinforces coherently. A hard-panned element exists in one channel only, so it has nothing to sum with. The result is that a hard-panned part ends up roughly 6 dB down relative to a centred one after fold-down. The exact figure depends on your DAW’s pan law and how the fold-down is scaled, but the relative penalty is large and it is real.

What it sounds like: at the desk, a balanced mix. On a phone, the hard-panned guitar or hi-hat has receded and the centred parts have taken over. The mix has not collapsed, it has re-balanced itself without asking you.

The nuance worth keeping: this is not an argument against hard panning. LCR mixing is built entirely on hard pans and it produced a lot of records that still sound excellent. It is an argument for knowing the price. If a part is doing structural work, do not hard-pan it. If it is decoration, hard-panning it is a legitimate choice and losing 6 dB of it on a phone is an acceptable trade.

The fix: ask what a part is for. Anything the song needs at all times sits centred or close to it. Anything that adds interest can go wide. If you want the width without the mono penalty, pair the hard-panned part with a counterweight on the other side so the mono sum keeps something in that role.

8. Lopsided Left/Right Balance

The least glamorous item here and one of the easiest to catch, which is exactly why it slips through — nobody looks.

What it sounds like: the image leans. One side works harder than the other and the mix feels subtly off-axis without any single element sounding wrong. On headphones it produces a peculiar kind of listening fatigue that is hard to name.

Why it happens: almost always accumulation rather than a decision. Three parts panned slightly left, one bright element hard right, a stereo sample that was never balanced, an asymmetric room that made you compensate in the wrong direction. Each choice was reasonable and the total is not.

What to measure: left/right balance in dB. Anything beyond about 1 dB of offset on a full mix is audible and generally unintentional. This is worth checking as a number rather than by ear, because your room and your own hearing are both asymmetric and neither is a trustworthy referee.

The fix: re-pan rather than reach for a balance trim on the master. A trim hides the offset without fixing the arrangement that caused it. The exception is a genuinely asymmetric source, such as a stereo sample that arrived lopsided, where correcting it at the channel is correct.

9. Hollow Centre From Mid/Side Over-Widening

A specific and increasingly common failure, because mid/side width controls are now standard in free plugins and the default gesture is to turn them up.

Why it happens: widening in mid/side means raising the side channel relative to the mid, which is the same thing as lowering the mid relative to the side. The centre of your mix — lead vocal, kick, snare, bass — lives in the mid. So a width increase is also a quiet, uncredited reduction of everything that matters most.

What it sounds like: spacious and slightly empty. The mix got bigger and the vocal got smaller, and because both happened at once it does not read as a level problem. People respond by pushing the vocal up, which produces a mix that is simultaneously too wide and too vocal-forward.

What to measure: A/B the widener at matched loudness and listen to the vocal specifically rather than the overall impression. Then fold to mono and check the vocal again, because that is where the loss compounds.

The fix: widen in bands rather than full range. Leave the low and low-mid width alone, apply the increase above the mids, and if the centre still thins out, lift the mid channel instead of only raising the side. Mid/side EQ is the right tool for this and iZotope’s widening walkthrough covers the mechanics with the mono caveats attached.

10. Wide in Headphones, Wrong on a Club System

Its own failure mode because a large PA punishes different things than a phone does, and if your track is going to be played on one, the phone check is not sufficient.

Why a club is harsher than a phone: three reasons stack. Subs are almost always run summed, so any stereo information below the crossover is discarded before it reaches the room. Most of the audience is nowhere near the centre line, so the stereo image they hear is whichever side is closer, meaning a part that only exists on one side may be effectively absent for half the room. And the room itself is reverberant enough to smear the fine detail that width was carrying.

What it sounds like: fine on monitors, then weak and directionless on a big system. The energy you thought you had turns out to have been spread across a stereo field the PA does not reproduce. Anything essential that lived in the sides is gone.

What to measure: the mono fold-down, but with attention on the sub band specifically rather than the overall level. Then ask a structural question rather than a technical one: if the sides vanished entirely, would the groove still work? For club and festival material the answer needs to be yes.

The fix: everything load-bearing — kick, sub, snare, the main hook — sits centred and survives fold-down on its own. Width becomes decoration rather than structure. It is a stricter version of the same rule that governs the rest of this article, and it is why club mixes generally read as narrower than headphone-oriented ones.

11. Width Used Where Depth Was Needed

The conceptual failure, and the one that wastes the most time, because the symptom is “flat” and the instinct is to reach for width. Width is left-to-right. Flatness is front-to-back. They are different axes and one does not fix the other.

What it sounds like: a mix where everything is wide, everything is loud, and everything is equally close. There is no foreground and no background, so nothing reads as important. Adding more width makes it wider and no less flat.

What depth is actually built from: four cues, all of them about distance rather than position. Level, because quieter reads as further. High-frequency loss, because air absorbs treble over distance. The ratio of direct sound to reverb, which is the strongest cue of the four. And early reflections and pre-delay, which tell the ear how big the space is and how far into it the source sits.

What to measure: nothing clean, and I would rather say so than invent a metric. This is a contrast judgement: does the mix have parts that are deliberately further back, and is the difference between closest and furthest big enough to notice? If every element has the same reverb amount and the same brightness, the answer is no regardless of what any meter reads.

The fix: decide the front rank and the back rank before touching a width control. Then create the difference with level, top-end and reverb amount rather than with panning. The front-to-back panner approach is the most practical version of this, and reverb choices and settings covers the space side of it.

12. Width Bolted On at the Master Instead of Built in the Mix

The last failure is a workflow one. A widener on the master bus is the most tempting fix on this list, because it makes the whole mix wider in one gesture and takes four seconds.

Why it does not work: mix-bus widening cannot distinguish between what should be wide and what should not. It widens the vocal, the kick, the snare and the bass at exactly the same rate as the pads and the ambience. The result is broadly wider and individually vaguer — width without placement, which reads as a loss of focus rather than a gain in size. It also carries every risk in failure 9, applied to everything at once.

What to measure: correlation before and after your bus chain. If the master processing is moving the reading substantially, it is doing more to the stereo image than you probably intended.

The legitimate version: a small, band-limited width adjustment above the mids at the mastering stage is a normal and useful move. The distinction is corrective versus compensatory. Nudging a mix that is nearly right is mastering. Using the master bus to manufacture width the mix never had is patching, and it is cheaper to go back and pan properly.

What belongs on the bus and what does not is covered in inside a professional mix bus chain.

The Mono Question, Settled

This is the argument that generates the most conflicting advice in mixing, and the reason is that the two camps are answering two different questions while using the same word.

The “mixing in mono is the secret” position is about balance. Stereo width is flattering. It creates the impression of separation whether or not you earned it, because two parts in different places do not have to compete. Take the width away and they compete immediately, so every level and EQ decision gets harder and more honest. That is why balance and carving decisions made in mono tend to hold up: mono is a stricter judge.

The “mixing in mono is a waste of time” position is about the stereo picture, and on that question it is simply correct. You cannot judge placement, width, or how effect returns sit around a source in mono, because none of those things exist there. Anyone who mixes entirely in mono and flips to stereo at the end has spent no time on half the medium.

Both are right about their own question, which makes the resolution straightforward:

• Mono is for balance, masking and phase. Get the relative levels and the frequency carving right there, where nothing is hidden.
• Stereo is for placement, width, depth and effects. These do not exist in mono, so judging them there is meaningless.
• Mono again at the end is for verification. One final fold-down before you render, to confirm nothing you added in the stereo pass disappeared.

And one caveat about the mono check itself, since it is the step people most often perform incorrectly: the mono button is a diagnostic, not a target. If you fold to mono and start fixing the tonal balance until the mono version sounds great, you will have narrowed the mix and probably dulled it, because you optimised for a playback condition that is not the primary one. Mono tells you what is broken. It does not tell you what to aim for.

Three Panning Systems, Compared

Most panning problems are not wrong positions, they are the absence of a system. If every pan decision is made independently by ear, the total drifts lopsided, nothing gets a decided place, and the mix ends up narrow by accident. These are the three approaches that actually get used, and they are genuinely different rather than variations on one idea.

The honest read: the system matters far less than committing to one. LCR is the most instructive to try if your mixes come out narrow, because it removes the option of nudging things slightly and forces you to decide what each part is for — you find out quickly which parts cannot leave the centre. Counterweighted panning is the most broadly useful for modern dense productions. Free panning gives the best results in the hands of someone already watching their balance meter and the worst in the hands of someone who is not.

Two rules survive all three systems. The rhythmic and melodic core — lead vocal, kick, snare, bass — stays centred, because those parts carry the song and the centre is the only position that every playback system reproduces. And anything you hard-pan should be something you can afford to lose roughly 6 dB of on a phone speaker.

Real Width vs Fake Width: Every Technique Ranked by Mono Survival

This is the table I would have wanted when I started. Every common way of creating width, what it actually does to the signal, and what happens to it when the channels sum. The pattern is consistent: techniques that create width from different content survive, and techniques that create width from the same content processed differently do not.

The honest read on width plugins: they are not banned and they are not free. A band-limited widener above the mids on a pad, a background layer or an effect return is a completely normal move that costs you almost nothing where it matters. A full-range widener on a lead vocal, a kick or a bass is trading the phone listener for the headphone listener, and most of your audience is the phone listener. The rule that covers every row of that table is that width should be spent on parts the mix can survive without.

Where Width Belongs, by Frequency

Width is not a single decision applied to a whole mix. It is a decision per frequency region, and the correct amount rises with frequency — because that is where the ear can actually use directional information, and where cancellation costs you the least. Treat these as starting points to test against your own material rather than as rules.

Read down that table and you have the reason band-limited widening beats full-range widening in almost every case. A single width control applied across the whole spectrum is applying the 8 kHz answer to the 40 Hz question.

The Five-Minute Mono Check

Four steps, in this order, before you render. The reason to do it as a fixed routine rather than whenever you remember is the RoEx finding: mono and phase problems appear at nearly identical rates in mastered files as in mixes, which means they are not being caught by the person mixing or by the person mastering. A routine is what catches the thing you were not suspicious of.

• 1. Fold to mono and note the level change. Utility plugin on the master, loudness before, loudness after. A small dip is normal. A large drop means side content was carrying real weight. Listen for which element moved, not only for the number.
• 2. Watch correlation across the whole song. Not one bar. Correlation tracks the arrangement, so the reading that matters is the worst one, and it usually belongs to one specific section — often the one where the pads and the doubles arrive together.
• 3. Confirm the low end is mono. Solo below roughly 120 Hz and check correlation holds near the top of the scale. One button, the single least negotiable item on the list.
• 4. Listen on a real mono endpoint. One physical speaker, a phone, or a Bluetooth speaker. This step is not redundant with step 1, because a fold-down plugin lets you rationalise a result you can still hear in stereo memory. A phone does not.

A useful addition if you have the time: check a level-matched reference track through the same four steps. It tells you what a commercial release in your genre actually does in mono, which is almost always less dramatic than people expect, and it recalibrates what “normal” looks like on your meters. How to use reference tracks covers the level-matching part, which is the step most people skip and the one that makes the comparison meaningful.

What the Measurement Data Actually Says

Two large datasets exist on this subject and they appear to disagree. They are worth putting side by side, because the disagreement is informative rather than a problem.

The apparent contradiction resolves once you notice the two datasets are measuring different populations and different thresholds. RoEx’s corpus is largely mixes submitted for checking, which self-selects for people who suspect something is wrong. Mix Analytic are describing the distribution across their analysed mixes. And “a mono compatibility problem” at a detection threshold is not the same claim as “loses real level in mono.”

Put together, the honest summary is this. A minority of mixes — call it one in six — have a genuine mono or phase fault, and those faults are almost never caught before release, which makes the five-minute check above disproportionately worth doing. Meanwhile the majority of mixes are not broken at all, they are simply narrower than they needed to be, which is a missed opportunity rather than a defect. Two different problems, two different fixes, and confusing them is why the advice on this topic is such a mess. Check mono so you know you have not broken anything. Then use the width you have been too cautious to use.

How MixingGPT Reports Stereo and Mono Problems

This is the section where I have a commercial interest, so here is the mechanism rather than the pitch. MixingGPT is a plugin that loads in Logic Pro, Ableton Live, FL Studio, Studio One, Cubase, Nuendo, Reaper, Bitwig, and GarageBand as AU or VST3 on Mac and PC. You drop an audio file into the chat — a full mixdown, a stem, a bus, an a cappella — and it returns a structured report.

What is measured on this topic specifically. The plugin computes the DSP facts offline from your samples before anything else happens, and those numbers travel with the file. For stereo behaviour the two that matter are stereo correlation and left/right balance in dB. Both are computed from the actual audio, so they are facts rather than impressions, and the model is explicitly prohibited from contradicting them or substituting an estimate. Alongside those it reports BS.1770 integrated loudness, true peak, RMS, per-band spectral balance, harshness and sibilance indices, presence-resonance, dynamics and punch via peak-to-loudness ratio and short-term crest, and clipping counts. Longer uploads are split into time-sections with measured timestamps, so a correlation dip that only happens in the last chorus can be pointed at directly.

How it is scored, exactly. The Mix Readiness Score starts at 10 and deducts against measured facts. Stereo is one of its dimensions and carries a budget of 1.5 points, allocated like this:

The second row is the one worth pointing out, because it is the part of this article encoded in software: a mix that reads as effectively mono is penalised, not rewarded. Failure 6 is not a rhetorical flourish. If the scoring only punished negative correlation it would push every user toward the narrow, safe, unremarkable result, which is the more common failure in the measurement data.

What the full report contains. Eight sections: an Executive Summary carrying the Mix Readiness Score plus the biggest strength and biggest limitation; a Mix Assessment scorecard with per-area scores including stereo; a Priority Fixes list grouped by severity where each finding states problem, evidence, impact, the move, and the check that confirms it; a Full Mix Diagnosis explaining the mechanism; a Translation read covering phone, laptop, car, club and mono playback; a Leave Alone section naming what is already working; Taste Options framing the aesthetic choices; and Next Steps in action order. You can also ask a scoped question instead — “does this survive mono?” — and get a focused answer with an area score rather than a full critique.

Where it falls short, and on this topic the ceiling is real:

• It hears a stereo mixdown, not your session. This is the hard limit on failures 2, 3, 5 and 7. It can measure that your mix has negative correlation and tell you it will cancel in mono. It cannot tell you which of your two vocal doubles has flipped polarity, whether the width came from a widener or from two real takes, or which layer to nudge, because all of those arrive as the same summed file. It is built to say it cannot tell rather than to guess, which is the correct behaviour and also genuinely less satisfying than a fabricated answer.
• The score is a judgement, not a measurement. The correlation and balance figures are facts. The Mix Readiness Score is an engineer assessment informed by them, reported to one decimal and deliberately labelled subjective. Anything advertising an objective mix score is overclaiming.
• It will not invent numbers. Outside the measured values it is given, it is prohibited from producing specific frequencies, dB amounts, ratios or millisecond times. So it will not tell you to mono below 118 Hz, because that figure would be fabricated from a 2-track. Recommendations come as moves to A/B.
• Practical limits. Audio analysis is in beta. MP3 and WAV only, up to 50 MB, with 4 to 5 minutes the accurate sweet spot. Pro Tools is not supported, because there is no AAX build. It needs an internet connection.

What it costs. Audio bills by decoded duration at 4 credits per started minute, so a 5-minute full critique is 20 credits and a 30-second check is 4. Free includes 10 credits a month shared across chat, images and audio. Starter is $9 for 75 credits (about 18 minutes of audio), Pro is $19 for 200 credits (about 10 full critiques), Studio is $49 for 600 credits (about 30). Nothing rolls over. Full breakdown on the pricing page.

When something else is the better pick. If all you want is a free one-off correlation and mono readout with no account, RoEx’s Mix Check Studio and Mix Analytic both do that well and I have cited both above. If you want a plugin that shows you a live vector scope and correlation meter while you work, that is a metering tool rather than an analysis tool and any of the free ones will do. If you want something to render a finished mix from your stems rather than tell you what is wrong with the one you made, see the comparison of 12 AI mixing plugins for the cloud options.

Which One to Fix First

Twelve failures is too many to act on at once, and the order matters because the destructive ones mask the cosmetic ones. Work in this sequence:

• Settle the low end first. Failure 4. Confirm everything below roughly 100 to 120 Hz is mono. It is one button, it is non-negotiable, and it changes the perceived weight of the whole mix, so anything you judge before it gets re-litigated afterwards.
• Then hunt cancellation. Failures 3 and 5. Polarity-flip every layered pair, check doubles and multi-mic sources, and identify any short-delay widening. These destroy information rather than misplacing it, and no later decision can recover what they removed.
• Then audit your wideners. Failures 2, 9 and 12. Bypass every width plugin in the session, including the one on the master, and re-introduce them one at a time with a correlation meter open. This is usually where the mono collapse in failure 1 turns out to live.
• Then fix the balance of the image. Failures 7 and 8. Check L/R offset as a number, and confirm nothing structural is hard-panned.
• Only now ask whether it is wide enough. Failures 6 and 11. With the foundation stable you can add width without wondering whether you are stacking it on top of a problem — and this is also the point to ask whether what you actually wanted was depth.
• Verify last. Failure 10 and the five-minute check. Fold-down, correlation across the song, low band, real mono endpoint.

If you only do one thing from this entire article: put a correlation meter on your master and watch it through one full playthrough. It costs nothing, it takes the length of your song, and it catches the two problems that a dataset of 7 million tracks says survive all the way into finished releases.

Frequently Asked Questions

Related Deep Dives in This Series

This guide covers the stereo field at mix level. The guides below go deeper on the individual decisions it touches.