The mix sounds enormous in headphones. Then it comes out of a phone, and the thing you spent the evening widening is quieter than everything around it, or gone. Nothing broke. The mix was summed to mono, and mono keeps only what the two channels agree on.
Where your mix actually gets played
A studio is two speakers, correctly placed, with one listener sitting in the middle of them. Almost nothing else is. A phone has one speaker. Most small Bluetooth boxes have one, or two so close together that the difference between them is academic. A laptop has two, a few centimetres apart, pointing at the ceiling. In a club the subwoofers are fed a summed signal, so everything below the crossover is mono before it reaches anybody.
None of these are edge cases. They are where the majority of listening happens, and they are the conditions your mix has to survive.
What happens when stereo collapses
A single speaker cannot play two channels, so the two are added together. That addition is the whole story. Anything present in both channels gets louder and stays. Anything present in one channel and inverted in the other adds up to zero and disappears.
It helps to stop thinking in left and right and start thinking in mid and side. The mid is what the two channels have in common, and the side is the difference between them. Summing to mono keeps the mid and removes the side. So the question is not how wide the mix is. It is how much of the sound only exists in the side.
Stereo wideners
The aggressive ones work by pushing content into the side, which is exactly the part mono discards. The wider it sounds on headphones, the more there is to lose.
Delay-based width
Copying a signal to the other channel and delaying it by a few milliseconds sounds wide and comb filters when summed, so the tone changes rather than just the width.
Low end in the sides
Bass and kick are the most expensive things to lose, and they are also the ones a club plays through a mono subwoofer. This is the one worth checking first.
Multi-mic recordings
Two microphones on one source arrive at slightly different times. In stereo that reads as depth. In mono it reads as a notch somewhere in the low mids.
How to check, in about a minute
- Sum the master to mono. Every DAW can do it, and most metering plugins have a button for it.
- Listen to the level first, not the tone. If the whole mix drops when you press it, something large is cancelling.
- Now solo the low end and switch again. Bass that thins out in mono is the most common finding and the most damaging one.
- Go through the wide elements one at a time: reverbs, pads, doubled guitars, anything with a widener on it. Switch mono on and off and listen for what leaves.
- Play it back on your phone, out loud, across the room. It is a worse speaker than anything in your studio and it tells the truth about the balance.
Reading a correlation meter
A correlation meter puts a number on how much the two channels agree, and it saves you from guessing. It runs from plus one to minus one.
| Reading | What it means | What to do |
|---|---|---|
| +1 | The channels are identical. The signal is already mono. | Nothing. This is what a bass line should look like. |
| +0.5 to +1 | Wide, and the two channels still mostly agree. | Nothing. This is a healthy mix. |
| Around 0 | The channels are unrelated. Very wide, and roughly half of it is in the side. | Worth a listen in mono. Fine for a pad, expensive for a hook. |
| Below 0 | The channels are working against each other, and mono is subtracting. | Find it and fix it. Below zero on the master is a warning, not a style. |
What to do when something disappears
The reflex is to narrow it, and narrowing does work, because it moves the sound back into the part that survives. It also costs you the thing you widened it for. There is usually a better move available first.
- Make the low end mono below a crossover point. Somewhere around 100 to 150 Hz is the usual starting point, and it fixes the most damaging case on its own while leaving everything above it as wide as it was.
- Find the one element doing the damage. It is rarely the whole mix. Mute the wide elements one at a time in mono and the culprit announces itself.
- Check the phase on multi-mic sources. Flipping the polarity on one microphone often recovers a low end you thought you had lost.
- Reach for the width you already have. Real stereo from a real performance, two takes, or a genuine room, survives summing far better than width that was manufactured from a mono source.
- Move the energy instead of removing it. Content that only lives in the side can be put into the centre, so it is still there when the mix collapses.
Width you can commit to
The last one on that list is the interesting one. A mix does not have to choose between sounding wide on headphones and sounding solid on a phone. What makes the choice feel forced is that the two decisions are usually made with one control, and turning width down is the only way to hear what mono will do to it.
MSBrooo injects the side energy back into the centre, so the mix holds up wherever it lands. It has a mono check on the front, and a correlation meter next to it, so the question this whole page is about is answered while you work rather than after you export.