Subtle difference in sound when recording stereo vs mono (no stereo fx)

Not really a problem here, just looking for a bit of insight.

I've always connected my kemper to two line inputs via main outs, and recorded onto a stereo track in my DAW. However as I very rarely use any effects in the post stack slots, I figured I should probably try setting the Output to "Master Mono" and just record to a mono track (via one cable).

The stereo signal is about 3db louder than the mono output, but even compensating for that, I'm hearing a subtle difference - if anything the mono track sounds slightly better - bit clearer, more punchy.

I'd have thought a mono track would sound exactly the same as a mono signal spread over a stereo track - but apparently not? Maybe I'm just missing some basic audio-engineering theory here, and this is not Kemper-specific?

But also, the two sides of the stereo track (again, just the amp stack, no stereo fx) do not seem to be exactly the same... With Kemper outs set to "Master Stereo" I recorded each side onto a separate mono track, and inverted the phase on one. They did not totally cancel out (very weak, barely audible sound, but still there). I then did the same with Kemper outs set to "Master Mono". In this case the two tracks cancelled out completely, as expected.

Can anyone shed any light on why the sound is slightly different when recording (with no stero fx) to a stereo track vs mono? And why - if the signal should be mono with no stereo fx added - does each side of the stereo output not cancel out completely if one side is phase inverted?

Thanks for the reply. Yes, not surprised by the 3db difference with 1 channel vs 2, was just wondering if there was some stereo width in the amp block signal after all. But as you say, must just be some subtle difference in the electronics.

Only thing I'd say it, this subtle difference in electronics does result in the stereo output being slightly less sharp and clear than the mono one - enough so that now I've compared the two, I will be unlikely to use the stereo output unless I'm using stereo effects in the Kemper.

One quick related question - if I use the "Vintage Chorus" in the Mod slot, does this effect automatically become mono if I set the Output to "Master Mono"?

Quote from Burkhard

Have you checked Space in Output Section as suggested? Depending on your settings it might influence the sound of your MAIN OUTPUT.

Master Mono mixes the signal to mono in the output stage, which is not the same as placing the Vintage Chrous in one of the mono modules A-D.

I suggest you connect both cables to a stereo channel of your mixing desk and switch between Master Mono and Master Stereo to investigate the impact.

Yes, space definitely off.

Got some spdif cables today, and tested them out (what I described above was all using the master outs to line inputs). Connecting via spdif, I found the two sides of the Stereo signal (again with no stereo fx) DID cancel out if one is phase inverted. Also, I could hear no longer hear any appreciable difference between the same part recorded to stereo track using the Mod Stereo setting vs recorded to mono track using the Git/Mod Mono setting (other than about the 3db volume difference which is to be expected).

So it does seem like something's happening when using the main output into line inputs which causes the two sides of the stereo out to be slightly different even when no stereo fx used. It's subtle, but it's enough to hear, maybe because it causes some sort of slight phasing or something which is why the mono line in sounded clearer/crisper/punchier?

Of course, this could be due to the audio interfaces line ins, not necessarily the Kempers analog outs.

Anyway, all these problems gone using spdif, so will use that from now on

I did test the vintage chorus in Mod slot with both stereo & mono output settings btw - my conclusion was it sounded much better in stereo (unsurprisingly I suppose!) So while I'll probably record most parts in mono from now on, I'll switch to stereo if I'm using the chorus (or other any stereo fx) in Mod slot.

Quote from jedseneca

If you are not using the effects after the stack then summed mono is the way to go. I am an audio engineer/ producer , musician and have many sessions under my belt in Nashville and LA. - mostly prior to Kemper days, and most recordings were mic'd mono. There was a time when the session players brought in racks and racks of processing gear and went stereo but now, they use amps that we mic and record multiple parts and they use pedals. When I am recording with the Kemper, I record summed mono if i want a 60's- 70's vintage vibe because the parts will be panned 70% left or right anyway in the mix then. I add space/ambience in my DAW with plugins. I only use stereo if I am creating an effected sound within the Kemper etc.

Thanks for the tips - I have indeed concluded that recording in mono is the best practice from now on - will just use stereo if I use the vintage chorus in Mod slot - most effects I do apply in the DAW, but I don't currently have any plugins that give me as nice a chorus (for guitars anyway) as the Kemper's Vintage chorus!

I've never been totally clear though - from a technical (audio engineering) point of view, what exactly is the difference between panning a mono signal spread across a stereo track (e.g. Kemper's Stereo Output with no stereo fx) and a mono signal on a mono track? I've noticed a stereo track loses a lot of volume the more it's panned - presumably because in this case the panner is just reducing the side of the signal you're panning away from? But even if you compensated by increasing volume, is there some difference/disadvantage?

Quote from ReinoutV

If there is no audible difference when using spdif, then it seems like the summing itself is not the issue. Have you checked the lengths of the XLR-cables? Is these are different, that could be a source of a very tiny mismatch in phase, I think. And when I say tiny, I mean really tiny.

They're identical cables. Though I suppose one could have some sort of flaw. Otherwise the difference has to be between either the Kemper l/r analong outs, or between my audio interface's inputs (as you say, the spdif acting as expected means it's not something more fundamental with the Kemper). I guess I'll have to do the same test with another line instrument (or try Kemper analogs thru different interface) to narrow it down.

Quote from jedseneca

As an audio engineer out of Nashville since 1986, I have never recorded a mono signal across 2 tracks for guitar unless we created some type of stereo ambient separation for a stereo effect. The human ear hears naturally in stereo so when mixing music, I mostly create stereo imaging by panning different instruments in the mix. I use stereo chamber reverb effects to create ambience on the instruments ( the send is usually panned straight up). You can hear my mixes (listen through good quality headphones as well as speakers) here: https://www.youtube.com/channel/UCWyZy0nxPIj3gv6jdPCRiVQ

I agree there's no reason to record a mono signal across two tracks - it's really just a geeky technical question - if, as in the case of of the Kemper (with no stereo fx used) the stereo signal outputs identical signal to left and right channel, how is this technically any different to a mono signal - which if routed to a stereo out, also has identical signals in each channel? The panning is more fiddly I suppose - stereo balancer doesn't seem to follow the -3db pan law so you'd need to compensate for volume loss if panning - and using stereo dual panners would end up layering identical signals on top of each other - much simple just to pan a mono track. Maybe I've answered my own question there... Or is there anything else that makes a stereo track with identical signals either side undesirable compared to a mono track?