"True Stereo" Reverbs

[slurpeefan]

I have been on the hunt for a stereo in stereo out reverb in eurorack that maintains the stereo signal path throughout the signal path. No summing to mono. Its crazy to me how many modules will say that they are stereo in and stereo out but will not mention that they sum, kinda defeats the purpose of having a stereo in for me. So far the only ones I can think of that maintain a true stereo path are:

Desmodous Versio (and electus)
Milky Way


Any other ones that I don't currently know of?

[TYGTRFB]

Qu-Bit Aurora? According to the web site, "Spectral reverb with true stereo audio IO."

[ggillon]

FX aid has a few stereo reverb algos. Don't know if it's "true" stereo reverb though

[scuto]

Does Starlab sum? In my brief search I've not found collective Edit: conclusive evidence either way.

[starthief]

Don't confuse "true stereo" and dual mono reverbs...

Dual mono completely separates the left and right channel, which is unrealistic. Sound from your left is still going to reflect off of walls on the right.

There are various ways to implement "true stereo" but they all involve mixing a bit of the L input into the R channel and vice versa, though maybe with some extra predelay.

Summing to mono and then processing that in a psuedo-stereo reverb really isn't bad, as long as the dry signal preserves the original separate L/R inputs.

[clwilla]

Don't confuse "true stereo" and dual mono reverbs...

Dual mono completely separates the left and right channel, which is unrealistic. Sound from your left is still going to reflect off of walls on the right.

There are various ways to implement "true stereo" but they all involve mixing a bit of the L input into the R channel and vice versa, though maybe with some extra predelay.

Summing to mono and then processing that in a psuedo-stereo reverb really isn't bad, as long as the dry signal preserves the original separate L/R inputs.

It can cause weird phasing issues, particular if there are stereo effects in front of it.

[mdoudoroff]

Does Starlab sum? In my brief search I've not found collective evidence either way.

Not 100% positive, but if Starlab follows the same model as Magneto, one copy of the inputs are summed for processing, the other pair head to an analog dry/wet mixer then to the outputs. In other words, the dry path is all analog, and you mix in the output from the digital processing.

“True stereo” reverb is a myth that just won’t die. Everything about reverb algorithms is synthetic. There’s no reason you can’t make discrete use of left and right information within a reverb algorithm, but it’s just not relevant to most reverb goals, most of the time, and there’s no inherent magic to it. All the magic is in the algorithm designer’s work. FX Aid definitely has a few reverb algorithms that make discrete use of left/right, mainly to simulate close reflections IIRC, but most FX Aid reverb algorithms do not, because it’s just not relevant. If you’re really obsessed with placing your modular voice inside a complex, reverberant space, I guess there’s the Tasty Chips ECR+. I think the Expert Sleepers Disting EX can also do convolution reverb. But a DAW plugin would probably be cheaper, more straightforward, and possibly better than either of those.

It can cause weird phasing issues, particular if there are stereo effects in front of it.

Lots of things can cause weird phasing issues, no?

[starthief]

Summing to mono and then processing that in a psuedo-stereo reverb really isn't bad, as long as the dry signal preserves the original separate L/R inputs.

It can cause weird phasing issues, particular if there are stereo effects in front of it.

Summing to mono doesn't cause weird phasing issues, it reveals an existing phase correlation issue.

Just placing stereo mics in a real room can give you phase correlation issues.

[scuto]

Does Starlab sum? In my brief search I've not found collective evidence either way.

Not 100% positive, but if Starlab follows the same model as Magneto, one copy of the inputs are summed for processing, the other pair head to an analog dry/wet mixer then to the outputs. In other words, the dry path is all analog, and you mix in the output from the digital processing.

Ah, gotcha. Thanks. It does sound like this is happening to some degree. A mono signal going in to Starlab certainly sounds wider coming out in stereo, but I've not investigated if it's a phase thing or something algorithmic.

[Artaos]

Tasty Chips ECR+ is “true stereo”. It’s a convolution reverb, so it needs quad impulse responses to be able to do that (respectively describing how the left channel reflects to the left and right, and how the right channel reflects to the right and left).

[tdallas]

Regarding the FX AID -> there was a discussion about stereo vs. summed L+R mono reverbs (with dry stereo field still in place) for those who are interested in:

[...] Shimmer is a special kind of effect which has no real world model. All reverbs related to real spaces and even plate have stereo in versions for those who use 100% wet sends.

Here is the list of stereo input reverbs: “Reverb Depth”, “Reverb Hall Chorus”, “Reverb Hall Chorus 2”, “Reverb Hall Medium”, “Reverb Plate stereo”, “Reverb Room stereo”, “Reverb Spooky”. Those reverbs handle early reflection according to the size of the relative space.
Most other reverbs are special kind of effects and do not need true stereo input.[...]

The "mono effect" L+R inputs are summed for the algorithm, but the stereo information in the dry portion is kept intact.

https://modwiggler.com/forum/viewtopic. ... 7#p3638557
https://modwiggler.com/forum/viewtopic. ... 8#p3638748
https://modwiggler.com/forum/viewtopic. ... 2#p3638962
https://modwiggler.com/forum/viewtopic. ... 0#p3639010

[tdallas]

I think the Expert Sleepers Disting EX can also do convolution reverb.

I thought the same, but not as "true stereo" from here:

[ersatzplanet]

If you are trying to simulate a real space, the summing shouldn't matter. A real space will "mix" right and left sounds too. If you are going for an unnatural effect, dual mono is the way, but it will sound unnatural for sure.

I use primarily FX Aid effects and had a email exchange with Igor (the developer) about this, as I was looking for a stereo in stereo out reverb. He explained what I said above and it made sense. It only becomes an issue when you want to pan the signal and use reverb on it also. Reverb post panner weakens the panning when it is mixed at the reverb, some more than others. Panning after the verb is kinda weird sounding for sure. Hard nut to crack well.

[bgribble]

A real space will "mix" right and left sounds too.

If you think about that statement for a moment, the problem with this whole line of discussion becomes clear. Stereo is an output format that's supposed to correspond to the signals you receive at your ears. It doesn't actually describe the source of the sound in any useful way, it just reproduces how the sound would "project" onto your 2 ears.

So it doesn't mean ANYTHING to talk about a "stereo input" to an artificial reverb that's supposed to model a space. If we put a real sound source in a real space, it's not a "stereo" source, it's just a source of vibrations in the space. Those vibrations bounce around the space and eventually land on your 2 ears.

Thought experiment: Imagine you have an actual gymnasium or other reverberant chamber.

First, let's imagine a single person singing. How would you get the best and most musical reverberant sound? I would suggest that you put the person in the space and use a stereo mic setup to capture the sound, moving around the person and the mics until you get the combination of direct sound, early reflection, and reverberation that makes you feel all squishy inside. Nice!

Now let's imagine that the singer's not available, but you have a recording of that singer from a close mic. How can we most closely match the live-recorded sound? I would say it makes sense to place a single speaker, playing the recorded signal, in the space, and a stereo mic setup. Likewise, move around the speaker and mics to taste. Pretty similar to the live case. Nice!

Now, let's imagine that you have a live choir. Seems straightforward that you set the choir up in the room, stereo mics, move around to taste. Nice!

Now the hard one: what if you only have a stereo recording of the choir? For the sake of simplicity, let's say they were singing in an acoustically dead space so there's no natural reverb. Now what? Are you going to just place 2 stereo speakers in the room? Where do you place them? There's nothing you can do here that's going to make it anything like the actual choir being in the room, in terms of how the sound interacts with the acoustics of the environment. The stereo speakers are going to phase-cancel each other more or less depending on placement, the best placement would probably have them right on top of each other but that would still have phasing issues in some frequency bands depending on the size of the speakers. Gross!

What if you sum the choir to mono, then play it out of one speaker in the space? Huh, still not like the actual choir being there, but at least it's not a total shitshow of phase cancellation. Mix in the stereo recording as the "dry" sound and you are getting pretty close. Maybe you keep the mics farther back from the source in the room, since you know that you are going to mix the dry sound in stereo later, and just try to capture the room sound. Nice? Definitely not as nice as having the choir there, but better than trying to take an output format and pretend it's a source!

[etckla]

If you are trying to simulate a real space, the summing shouldn't matter. A real space will "mix" right and left sounds too. If you are going for an unnatural effect, dual mono is the way, but it will sound unnatural for sure.

I use primarily FX Aid effects and had a email exchange with Igor (the developer) about this, as I was looking for a stereo in stereo out reverb. He explained what I said above and it made sense. It only becomes an issue when you want to pan the signal and use reverb on it also. Reverb post panner weakens the panning when it is mixed at the reverb, some more than others. Panning after the verb is kinda weird sounding for sure. Hard nut to crack well.

From my basic research panning a mono reverb so it sits "behind" (or just out of the way of) a panned dry signal is a way to get clarity in a mix

I don't have enough reverbs, mixer channels or panners to validate that!

I have an Empress reverb pedal. I can confirm that sending panned signals into it does usually impact the "position" of the reverb, but the exact effect depends on the algorithm in use.

[hypnoz]

Qu-Bit Aurora? According to the web site, "Spectral reverb with true stereo audio IO."

Aurora is not really a reverb in the sense most people mean it. Its alt firmware FDN Verb does act as a sort of “stereo” reverb. Meaning, things panned left/right will make the reverb louder in their respective channels.

[clwilla]

Qu-Bit Aurora? According to the web site, "Spectral reverb with true stereo audio IO."

Aurora is not really a reverb in the sense most people mean it. Its alt firmware FDN Verb does act as a sort of “stereo” reverb. Meaning, things panned left/right will make the reverb louder in their respective channels.

Aurora isn’t really a reverb at all. It’s a re-synthesizer in the vein of endless processor or Panharmonium. You can definitely do reverb-y stuff with the time stretching, but it’s not a reverb.

The alternative firmware is much closer to a standard reverb.

[SynthBaron]

I've always found mono input to stereo reverbs sit better in the mix for whatever reason, and I think that's the reason they're the defacto standard.

[hypnoz]

Qu-Bit Aurora? According to the web site, "Spectral reverb with true stereo audio IO."

Aurora is not really a reverb in the sense most people mean it. Its alt firmware FDN Verb does act as a sort of “stereo” reverb. Meaning, things panned left/right will make the reverb louder in their respective channels.

Aurora isn’t really a reverb at all. It’s a re-synthesizer in the vein of endless processor or Panharmonium. You can definitely do reverb-y stuff with the time stretching, but it’s not a reverb.

The alternative firmware is much closer to a standard reverb.

Agreed. FDN Verb firmware is pretty basic but at least it does not sum the input stereo signal like most

[linear.b]

Synthtech E520 Hyperion?

I think white rabbit is but I haven't played enough to be sure; it wasn't a very expensive module so it wouldn't surprise me if it's summing.

[goldi]

Summing to mono and then processing that in a psuedo-stereo reverb really isn't bad, as long as the dry signal preserves the original separate L/R inputs.

It can cause weird phasing issues, particular if there are stereo effects in front of it.

Summing to mono doesn't cause weird phasing issues, it reveals an existing phase correlation issue.

Just placing stereo mics in a real room can give you phase correlation issues.

haha true, if anything it'll solve your phase issues

[BLogic12]

I love how much great info there is here but the original poster still hasn’t responded!
Their mind must be blown and be questioning their life’s reverb choices and desires.

[Jonachi]

I'm currently working on one, will be pretty huge in size though and lofi.

[slurpeefan]

I love how much great info there is here but the original poster still hasn’t responded!
Their mind must be blown and be questioning their life’s reverb choices and desires.

Nah I'm here and I fully expected this discussion because I worded things the way I did on purpose to get it. Stereo is a very interesting and kind of can of worms topic especially if your talking about recreating physical spaces.

[BLogic12]

I love how much great info there is here but the original poster still hasn’t responded!
Their mind must be blown and be questioning their life’s reverb choices and desires.

Nah I'm here and I fully expected this discussion because I worded things the way I did on purpose to get it. Stereo is a very interesting and kind of can of worms topic especially if your talking about recreating physical spaces.

The fact that you think it’s so crazy that so many reverb modules do some kind of summering, and that it defeats the purpose stereo made me think maybe you didn’t quite understand WHY that is (because if you did it wouldn’t be that crazy).

But yeah it’s an interesting discussion, good topic for sure.