Search for a stereo plugin and you get a list that mixes four different kinds of tool together. They all say stereo on the box, and they are built for different problems. Buying the wrong kind is why people end up with three of them on the master and a mix that still falls apart on a phone.
The four kinds
Wideners
iZotope Ozone Imager, Waves S1 Stereo Imager, Polyverse Wider, A1StereoControl, Leapwing StageOne. They increase the difference between your two channels, which is what makes a mix sound bigger on headphones.
Mid/side utilities
Voxengo MSED, Waves Center, Brainworx bx_control. They split a stereo signal into mid and side so anything else, an EQ or a compressor, can treat the two separately, then put it back together.
Imaging meters
Vectorscopes, goniometers and correlation meters, built into most metering suites. They process nothing. They tell you how much of the mix is in the side and whether the channels are fighting each other.
Mono makers
Usually a control inside a widener or an EQ rather than a plugin of its own. They collapse everything below a crossover point to mono, which is the standard protection for the low end.
What each kind is actually for
| The problem | The kind of tool | What it does about it |
|---|---|---|
| The mix feels small and flat in headphones | Widener | Raises the side, so the picture spreads out |
| The top needs to be wide and the bass needs to be solid | Mono maker | Collapses everything below a crossover, leaves the top alone |
| The centre needs compressing without squashing the room | Mid/side utility | Lets a compressor work on the mid alone |
| Something disappears when the mix is summed | Imaging meter first | Tells you how much lives only in the side, and where |
| The width is right and mono still takes the weight out | See below | Moves side energy into the centre instead of removing it |
Why a widener cannot fix a mono problem
This is the part worth being clear about, and it is not a criticism of any of them. A widener raises the side signal. Summing to mono removes the side signal. So the more a widener does its job, the more there is to lose when the mix reaches a phone speaker or a club subwoofer.
That is not a fault. A widener is built to make a mix bigger on a stereo system, and it does. It is simply not the tool for the question of what survives when the two channels are added together, and reaching for a wider setting when a mix sounds thin in mono makes the gap larger rather than smaller.
The usual answer is to narrow instead, which works, and costs you exactly the width you widened for. That is the trade most producers accept without noticing they are making it.
Choosing, in one pass
- Start with a meter, always. Guessing which of the other three you need is how people end up owning all of them.
- If the mix is genuinely narrow and sounds small on good speakers, you want a widener.
- If the low end is the problem, you want a mono maker and a crossover. This is the most common answer and the cheapest one.
- If you want to treat the centre and the edges differently with tools you already own, you want a mid/side utility in front of them.
- If the width is right and mono still takes the body out of it, none of the four is the answer, because all four either add side, remove side, or measure it.
The fifth thing
There is one more move available, and it is the one the shelf is thin on: keeping the width and moving what would be lost. Energy that exists only in the side can be filtered and summed into the mid, so the stereo picture stays exactly where it is and the weight is still there after the collapse.
MSBrooo injects the side energy back into the centre, so the mix holds up wherever it lands. It has the mono check and the correlation meter on the same panel, so the measuring and the deciding happen in one place instead of three.