It’s funny how trends fluctuate. I see it regularly at my workbench – all of a sudden, I get a drove of requests for the same modified pedal, then it dries up. Then there’s another pedal that everybody wants, until that dries up. And on to the next one… 🙂 You can see it clearly on the various discussion forums as well – for a time, everybody wants to know about a certain thing, and then it shifts over to something else. One thing that has been in the spotlight for quite some time now is the subject of summing to mono.

The premise is that you have a stereo setup, but occasionally want to play with just one amp. Why not sum the two outputs to mono, so you won’t lose any of those nice stereo delays etc?

I can see the temptation here – wanting to get as much as possible from the effects, thinking that you’ll otherwise lose half of them. And sometimes, it will work just fine. But other times, it will produce less than desirable results, and this article will detail a couple of reasons why.

1+1=3 (or more)

When you spread the effects out to stereo L/R channels, the wider sound canvas created will fit more effects than you’d otherwise be able to find room for. Take, for instance, the ping-pong delays – in stereo, they can (and often will) be set louder, with more repeats at a faster rate, than you would do with a single mono delay. This is simply because the ping-pong delay is panned out to the sides, out of the way of the main guitar signal. Usually, I find that mono setups require more subtle settings – since you can’t simply pan the delay out of the way of the guitar, you need to find other ways to distinguish it from the dry signal. For me, that usually involves turning the delay down, and using a delay that is filtered (so the repeats have a slightly different tonality to them).

The same applies to many other effects, I’ve found. A stereo chorus or flanger can be much wetter, while the same chorus in mono needs to be turned down a fair bit to stop it from drowning out the dry signal to the point where you start losing the initial attack. Remember, a chorus or flanger is – at heart – a short delay, and if you get to the point where the delayed signal takes over, it will start to feel like your playing is ever so slightly delayed. Actually, it is, but you get the drift. Going from mono to stereo (or vice versa) will often require changes to the effects settings, so simply flicking a switch to sum a stereo setup to mono usually won’t work as well as one might think.

Phase related problems

A lot of the stereo imaging that goes on in the effects we use rely on very short delays, shifting the timing ever so slightly. In fact, tiny differences in the time different sounds reach our ears is the basis for how we position different sound sources, and a digital reverb tries to make itself as wide as possible using different timed early reflections. All of this is all fine when we feed the left and right signals to a stereo setup, but when you sum both into a single mono signal, some of those sounds – the ones that are very close in time – will start fighting each other out. You may then end up with weird phase/comb filter effects you didn’t want.

And sometimes, summing to mono will simply cancel the effect out completely. For instance, many chorus pedals are made stereo by simply inverting the phase of the chorus signal going to the second output. If you then sum that to mono, the two chorus signals will cancel each other out, leaving you wondering what happened to that beautiful chorus effect…

Panning is a cool effect in stereo – somewhat related to tremolo, but more visceral. Normally, if you used a panning effect in mono (by hooking up just one side of the effect), it will simply turn itself into a tremolo. But if you sum the two channels to mono, most of the panning effect will disappear. You may hear a slight wobble in the signal as it goes past center in the stereo image, but that’s about it.

What to do?

First off, don’t expect to be able to use 100% the same settings in mono as you do in stereo – the two situations are different, and should be treated as such to get the best results. It is much better to create specific sounds/settings that work in mono, rather than try to cram a stereo sound into one amp. That ping-pong delay which works so well in stereo? In mono, you’d probably be better off with just half of it. That chorus which in stereo sounds so lush and yet won’t overpower the core tone? In mono, you’ll most likely have to dial it down quite a bit to get a similar effect.

To get a full mono setup, ideally you should remove all the additional cabling as well, to go mono all the way through the pedal chain. But that is a lot of work, so in most cases, simply leaving the chain intact and skipping one of the two output cables is all you need to do.

There are a couple of things to look out for, as always. Some pedals alter their behaviour depending on which output(s) are in use, and those may need special attention. For instance, if you have a delay pedal upstream in the chain which splits the signal into one 100% wet and one 100% dry output (Boss DM-3, DD-2/3 etc), leaving both outputs hooked up while you skip one of the sides at the end of the chain may not be what you want. In that case, you need to pull the cable from the ”B” output and use the side of the chain which is fed from the ”A” output.

Also, some stereo input pedals are designed to sum both inputs to mono if you use both inputs but only one output. If you use such a pedal in the middle of the chain, it’s all good. But if it’s the last one, it will actually do exactly the opposite of what you want (or at least, what this article argues you shouldn’t want 🙂 ). In that case, try leaving a plug in the second output. That will stop the pedal from summing the signals at the end.

But I’ve tried summing, and I like it. That means you’re wrong, doesn’t it?

Not really. It does mean you have had a different experience than me, and you should of course always do what works for you. As I mentioned at the beginning, in some setups – with those specific effects etc – summing can work well. Other times, not so much. And over the years, I’ve come across many of those ”other times” examples. It’s not about right vs wrong – I’m merely here to give my view on the subject, while also providing a possible explanation to those who have tried it and gotten weird results. But if it works for you, don’t let any blog – yes, not even this one – or forum discussion overrule your own ears!

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