The typical way stereo signals are converted to mono is by summing left and right (and perhaps attenuate the result).

Obviously, the sum approach does a poor job capturing the side material, as the greater the difference is, the more the input signals will cancel each other out.

Are there any other (perhaps more creative) methods that will allow the side events to make it through in a mono conversion?

(I ask because I've noticed that some wireless mono speakers, like SONOS PLAY 1, sound like they include side channel material somehow along with the mid/center, which I can't get my head around)

2 Answers 2


Off the top of my head..

Sum - Adds Signals; any sounds present in both signals are reinforced by a varying amount, depending on how in-phase they are.

Subtract - Subtracts one signal from the other(same as inverting the phase of one, then adding it to the other); any sounds present in both signals are attenuated or cancelled out completely, depending on how in-phase they are.

You could add (Sum + Subtract) together, but you would be left with one of the input channels(L or R) being attenuated.

The only method I can think of is to delay one of the stereo channels, then add it to the other, to limit the reinforcement.
You could even try applying a stereo delay to just the mono element before summing.


Your suggestions resemble some of the strategies used in the Mid-Side technique.

Mid = L+R Side = L+(-R)

If there's a gain difference I think you can compensate by multiplying the signal with the sqrt(0.5). Something like 0.707... (Correct me if I'm wrong)



https://en.wikipedia.org/wiki/Microphone_practice#M/S_technique:_Mid/Side_stereophony https://www.uaudio.com/blog/mid-side-mic-recording/

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