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Stereo summing.  On the surface it’s a great feature that allows you to wire your compatible pedals in stereo, but switch to using them in mono at the push of a button.  Very handy if an amp dies mid-set or if you go from being able to use two amps to one at different venues and don't want to rewire your board. 

It does this by merging the left and right side of your stereo signal together and then sending that merged signal to both the left and right amps or outputs. But is stereo summing more hype than practical?  


And yes.  

It depends. 

Summing was originally put into our products (from LongLine, Interfacer, Underfacer, Output TX, Wet Dry Wet Box and more) as a fail-safe.  If you were running a stereo rig and one of your amps died mid-gig, you’d simply sum your signal by holding a footswitch or pushing a button and both the left and right outputs would get a summed (mono) signal.  Regardless of which amp went down, you wouldn’t lose half of your delay repeats.  Once your amp was back up and running for the next song or show, you could go back to stereo again, seamlessly.  As musos started using summing as a convenience, more questions started popping up around summing and its possible drawbacks. 

As is often the case, there isn’t a black and white answer when it comes to summing your stereo signal.  As musicians, we have become accustomed to a bit of a wrestling match to find our ideal tone.  There are very few ‘easy’ answers and most ground towards the ‘best’ tone is hard won.  

Questions like, ‘How should I run my rig?’. Mono, dual mono, stereo, wet dry, 4 cable method, wet dry wet, 5 cable method? Or, ‘What is the best overdrive?’. How do I get rid of noise in my rig? All of these questions begin with a similar answer - “It depends…” 

The same goes for stereo summing.  You can’t ask the question, “Will summing work for my rig?” and get a black and white answer.  “It depends''.  

Why would summing even have the potential of affecting your signal you may ask? What are we even talking about?  There are certain effects like chorus, phaser, flanger, tremolo that, when run in stereo, have an effect that is slightly or entirely out of phase between the left and right outputs.  This is by design.  The effect wouldn’t be the same without it.  When you run these same effects in mono, they correct any phase issues internally and it still sounds great.  

The potential problem lies in trying to sum a modulation pedal to mono when it has been plugged in (using the left and right outputs) in stereo.  Now you are trying to sum or merge two signals that are slightly or entirely out of phase with each other.  

What does this sound like? 

Let’s go through summing at it’s best and summing at it’s worst below. 

Underfacer Summed to mono

Summing at it’s best

Where does summing really shine?  

Delay, Reverb and some modulation effects tend to do a great job with summing.  Although I will avoid using the word, ‘Always’, the ping pong effect of a stereo delay is often translated accurately to a summed signal.  Similarly with reverb.  Where you start to notice more significant differences is when you have a delay or reverb with built in stereo modulation.  The modulation portion of the signal can have the same reduced effect as mentioned above when summing.  

As an example, if you’re using something like a boss DD5 for your stereo delay and a TC Electronic Hall of Fame for reverb, summing will work really well.  If you move over to a Strymon Timeline and Bigsky and go heavy on the modulation, you will notice the modulation portion of your signal diminish when summed.  

Again, a lot of delay algorithms are not ping pong-ing back and forth between your left and right outputs.  Timeline by Strymon as an example only has two delay options (pattern and dual) that actually go back and forth between the left and right outputs.  All other options from Lo-Fi, filter, trem, swell, duck, ice, reverse, digital, dbucket and dtape are all dual mono with some sort of slight stereo modulation layered underneath. Which means the worry of using ‘Split Sum’ (more on this below) and muting half of your delay repeats is not something you’d even need to consider! 

Interfacer Dual Mono
Summing at its worst

With some modulation (certain chorus, tremolo, phaser, flanger pedals), summing a stereo signal can sound like a reduction in the effect level.  Almost like you’ve turned down the depth or mix level of the effect.  With some stereo tremolos, which can be 180deg out or opposite polarities, this can completely erase the effect and sound like it’s in bypass.  

The reason I use the word ‘some effects’, is that not all pedals use the same approach.  I warned you, there are no black and white answers here.  Strymon Flint as an example (a stereo reverb and tremolo in one pedal) sums really well because it is not a stereo panning tremolo.  Both the left and right outputs see the same pulse at the same time.  Certain stereo chorus pedals send the left output as dry and the right output as a chorus effect.  These also sum really well because they aren’t canceling out part of their signal.  

Due to this ‘worst case scenario’ we implemented a new type of summing into our product line back in 2018.  We now have two summing options: 

Stereo Sum - This is what has been written about up until this point.  It takes the stereo output of your pedalboard, merges the left and right signals together with impedance matched buffers and then splits that merged signal to both the left and right outputs.  This is great for delay and reverb but tends to cause phase cancellation in some modulation. 

Split Sum - With internal DIP switches on our products you can select Split Sum.  This takes the stereo field from your last pedal, mutes the right side entirely and splits the left output to both the left and right outputs.  No phase cancellation anymore.  This is better for modulation but not great for ping pong delays. 

If you use both heavy modulation and stereo ping pong delays, there isn’t going to be a perfect solution for you other than running your signal in stereo or mono.  Not both.  In this scenario I’d recommend running stereo and using summing as a fail safe (only in the case an issue comes up on your rig and you need to sum your signal to get your delay repeats back to one amp). 

Here’s a bit of a checklist for workarounds / options if you feel you really need to have summing as an option.

  1. You can run your modulation in mono, then split to stereo at your delay and reverb effects 
  2. You can use split sum or stereo sum options on Goodwood products and see which suits you best
  3. Always run mono (or dual mono) and avoid stereo entirely. 
  4. Test each individual stereo pedal to see how well they sum / don’t sum.  
  5. Make it easy to unplug the right side of each modulation pedal if you need to run mono.  Plug them all back in for stereo. 

It’s a detail oriented world for us guitar players filled with a bunch of, ‘maybe’s’, ‘sometimes’, and ‘only when the sun is shining on a Wednesday after 3pm in fall will you have to worry about that…’ 

You need to test your personal rig, specific pedals, preferences and settings to see what is going to work! Not all modulation is the same, not all delays ping pong and I hope I'm not alone in saying, sometimes your rig is dripping in tone and other days you’re struggling to get sound to come out the other end.  This is a fluid tonal pursuit we’re in and just when you think you’ve got it dialled, something will change.  

I hope you take the above with a grain of salt.  There are people who agree with what I’ve said and plenty that don’t.  Test it for yourself before you take anyone's word on tone as ‘gospel’.  

If you want to hear any of these examples I’ve done videos on our YouTube Channel going through different rig options, routing, best practices etc.  


See you a bit further down the road to Tone Town! 


By Grant Klassen


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