There’s something slightly unfashionable about mixing in mono. We spend so much time talking about stereo width, immersive mixes and making things feel bigger that deliberately collapsing a mix down to one speaker can seem like going backwards. But mono is still one of the most useful reality checks you have in a mix.

There’s some simple skills you can learn today so your mixes are much less likely cause you translations issues in the future, but first you need to understand why your mixes sometimes don’t sound great on other devices – and what you can do about that.

Stereo Can Hide a Lot of Problems

A wide stereo mix can sound fantastic while you’re sitting between your monitors. Instruments have their own little patches of space, reverbs spread out around them, and panning helps separate things that might otherwise be competing. But sometimes you’re not actually fixing the problem. You’re just moving it somewhere else.

Take a kick and bass. In stereo, they might appear to sit nicely together, especially if the bass is slightly off to one side or has some stereo processing. Collapse the mix to mono and suddenly they’re fighting for the same bit of frequency real estate.

The same thing happens with guitars, keyboards, backing vocals and pretty much anything else you’ve managed to spread around the stereo field.

Mono forces you to make an actual balance decision.

You can’t rely on panning to keep things apart. If two instruments are occupying the same space, you have to deal with the problem, whether that means changing the arrangement, adjusting the levels or reaching for the EQ.

This is one reason I like mono as a mixing tool. It makes certain problems rather difficult to ignore.

Mono Is Also a Phase Check

This is probably the more important reason to keep the mono button close by. Stereo effects can introduce phase problems that aren’t particularly obvious when you’re listening in stereo. Delays, chorus, stereo widening and certain reverb techniques can all create differences between the left and right channels. That can sound great in the studio, until the two channels get combined.

Phones, laptops, Bluetooth speakers and some sound systems can produce a listening experience that is effectively mono, or at least much less stereo than the carefully arranged image you were monitoring in your studio. Not everyone listens to your music in a perfectly tuned studio control room with acoustic treatment.

If parts of your mix disappear, become noticeably thinner or suddenly sound hollow when summed to mono, you’ve found something worth investigating.

It doesn’t necessarily mean the stereo effect is bad. Sometimes you absolutely want that wide, phasey thing. The point is knowing what happens when the stereo information isn’t there anymore.

A mono check is a very quick way of finding out.

EQ Decisions Get Easier in Mono

One of the things I find useful about mono is that it makes frequency clashes much more obvious. That low-mid buildup you couldn’t quite put your finger on? There it is.

The vocal that seems perfectly clear because the guitars are spread left and right? Suddenly they’re competing for attention. When everything occupies the same central space, you get a much clearer picture of what is actually happening with the arrangement and frequency balance.

This doesn’t mean you should EQ your entire mix in mono. Please don’t do that. Stereo is part of the music, and if you spend the whole session with everything collapsed into the centre, you’re going to make decisions based on a listening condition that isn’t your final mix.

But switching to mono while making EQ and level decisions can be incredibly useful. Sometimes a tiny cut is all it takes to make two instruments behave. And sometimes you discover that no amount of EQ is going to fix the problem because the real issue is the arrangement. That’s useful information too.

Don’t Mix in Mono All Day

This is where I think some advice about mono gets a little too religious. You don’t need to spend your entire mixing session in mono. You’re not trying to recreate a 1960s radio mix, and there’s nothing inherently more professional about making everything come out of the centre speaker.

Use it periodically.

I’ll often check mono after a significant arrangement change, when I’ve made a big EQ decision, or when I’ve been messing around with stereo effects for a while. It’s particularly useful once a mix starts getting complicated, because that’s when stereo can make everything sound separated even when the underlying mix isn’t really working.

I’d also pay particular attention to the kick and bass. If the low end falls apart when you sum to mono, you want to know about it.

Then check the vocal and main melodic instruments. If they remain clear without the benefit of stereo separation, you’re generally in a much safer place.

And here’s another thing worth doing: listen to commercial tracks you know well in mono.

It’s surprisingly educational. You start hearing how much of a great mix is actually built around balance and arrangement rather than simply throwing things wide.

Don’t Let Mono Make You Overcorrect

Once you start hearing every little phase interaction in mono, it’s tempting to “fix” everything. That’s not necessarily the right move.

A stereo chorus might lose some energy when summed. Fine. A wide delay might become less obvious. Also fine. The question is whether the effect is causing a meaningful problem in the way people are likely to hear the song.

You can make a technically perfect mono-compatible mix that sounds smaller and less interesting in stereo. That’s not really a win.

Mono is a diagnostic tool, not the boss of your mix.

Understand the Goniometer

The goniometer is a great second opinion for your mix. It can reveal obvious stereo and phase problems pretty quickly, but it’s also useful when you’re experimenting with different spatial ideas. Here’s a brief crash-course in using one.

In Reaper, I’m using the fantastic free Goniometer from Tukan Studios. I highly recommend grabbing it, although most goniometers work in roughly the same way.

When the plugin is receiving audio, you’ll see a constantly moving cloud of data showing the relationship between the left and right channels. A broad, almost circular pattern generally indicates a lot of stereo information, while a narrower, more vertical pattern usually suggests better mono compatibility. Ideally, you’re looking for a tall, fat oval shape.

You want the display to be reasonably balanced between left and right, although some movement is completely normal depending on the music. Don’t expect a perfect shape, because different instruments and arrangements will produce very different patterns.

The phase correlation meter is particularly useful. It shows how similar or opposed the left and right channels are. +1 means the channels are identical, effectively mono, while 0 means they are largely uncorrelated. Negative values indicate increasing phase opposition between the channels.

For a typical stereo mix, you generally want the correlation to spend most of its time in positive territory. If it regularly drops below 0, it’s worth investigating, particularly if you’re using wide stereo effects. Sustained readings well into the negative range can indicate serious mono-compatibility problems.

When adding reverbs, delays and other stereo-enhancing effects, keep an eye on the goniometer. It can be a very useful reality check, telling you when you’re adding useful width and when you’ve perhaps pushed the stereo image a little too far.

The Real Benefit Is Translation

The biggest practical advantage is that your mix has a better chance of holding together on different playback systems.

A song that works on studio monitors but falls apart on a phone isn’t particularly useful to anyone, and most listeners aren’t sitting in the exact sweet spot you’ve been occupying for the last six hours.

Mono checking can help reveal weak low-end relationships, masking and phase problems before they become somebody else’s problem.

It can also make you a little more decisive. If you keep adding stereo width because the mix feels crowded, collapsing it to mono can expose the fact that you’ve got six instruments all trying to occupy the same frequency range. Suddenly the solution isn’t another plugin. It’s turning something down, changing an EQ, or maybe removing a part that didn’t need to be there in the first place.

An Old Trick That Still Works

Mono mixing isn’t an outdated technique that we only keep around because engineers used to have one speaker. It remains useful because the underlying problem hasn’t changed. We still have to make instruments work together, we still have to deal with frequency masking, and we still have to make our mixes survive outside the studio.

Stereo gives us space and creativity. Mono gives us a rather blunt reality check.

So next time you’re halfway through a mix, hit the mono switch. Listen for a minute. Check the kick, bass, vocal and main instruments. Listen for things disappearing, fighting or suddenly sounding much different than they did in stereo.

Then switch back.

You might find that the stereo mix sounds better afterwards, not because mono made the mix more exciting, but because it made you fix what was underneath it.

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