Expanded mono downmix options

[Thebigcheese]

I realize this has come up many times before (this thread from several years ago is particularly relevant), but the behavior hasn't changed and it's still a frustrating user experience in my opinion. The issue is that when a user is using an audio interface that only presents stereo pairs of inputs to the OS, they will want to check the "Mono" checkbox in the advanced audio properties so that their mic is correctly seen as a mono source; however, doing this results in a 6 dB decrease in volume that needs to be corrected. I imagine many users don't even realize they need to correct for this and think they can increase their mic gain, which just results in distortion and they won't know why since it doesn't appear to be clipping. I understand why this 6 dB decrease is applied, but I think the user should have more options to account for different use cases. I have several ideas for ways to do this, but the first one is, I think, the least confusing and (probably) the least annoying to implement, but I'm not a programmer, so maybe I'm wrong. I'll also note that there are a few 3rd party workarounds for this, but I feel like this is something that shouldn't need a workaround.

My leading idea is to replace the current "Mono" checkbox with a dropdown list (or similar). This would have four options:

1. "Source": This is just the original stereo (or mono, if it's a mono source) audio, no changes. This is the same as not checking the current "Mono" box.
2. "Mono (downmix)": This works the same as checking the current "Mono" box. Left and right channels are combined with the -6 dB adjustment applied so it doesn't clip.
3. "Mono (L only):" Produces a mono signal, but rather than downmixing, it simply removes the right channel from the signal and does not apply any gain adjustment (or boosts by +6 dB if the -6 dB cut is the default behavior). This is effectively the same as checking the current "Mono" box, setting the balance to all the way left, and adding a +6 dB gain filter.
4. "Mono (R only):" As in #3, but with the left channel removed.

Ideally, the pan/balance behavior would also be updated so that the resulting mono signal can be panned. Currently, it just adjusts the balance of left and right in the resulting mono file rather than letting users pan the mono output. I like this idea because it seems easy to understand and doesn't clutter the input list with a bunch of inputs.

A second option would be to add a new channel mixer filter that works similar to the Reaper plugin described at the end of the thread linked above. The "Mono" checkbox could probably be removed entirely in this case as users would be able to decide for themselves how they want to mix and match the channels. This option is also pretty simple, but I don't think it's quite as user friendly as the first one. Still, maybe it's even easier to implement.

A third option would be to have OBS allow users to select just one side of a stereo input when selecting an audio input device, but I imagine this would be more annoying to implement. On top of that, there are a handful of interfaces that already do this (the Audient EVO 8 is an example), so this would end up creating duplicates of those and users would end up with a massive and confusing input list. So while it seems user friendly on the surface, I actually think this is the worst option when you dig into it.

As I said, I'm not a programmer, so I don't know how easy or hard any of these are to actually implement. But I do think that probably 99% of people using the "Mono" checkbox are people trying to work around weird audio interface limitations and not people downmixing a stereo source, so even if the current implementation is technically correct (and it is), it isn't really a good solution since no one uses it that way. I would love to see this updated eventually.

 

[nilanka]

Hi,

I have been going nuts thinking it’s me. Could I know why that -6db reduction happens please? I can route my mic signal to the other channel as well using the interface and I’ve been doing that to avoid this -6db reduction.

 

[Thebigcheese]

It's a pan law thing. Technically, if you have a stereo source where you have the same signal on both channels, you would need to subtract 6 dB when summing to mono to achieve an equivalent signal level. So it makes sense, but given that many audio interfaces come in as "stereo," there are definitely better ways to handle it.

 

[nilanka]

Thank you for explaining that. So what I was doing probably isn’t technically right… But you’re right, a bit more control for the user would help in this case.

 

[x Hades Stamps]

I know this thread is nearly a year old by now, but I just want to add that there are scenarios where none of those options work (for example, singing with a guitar connected to the other input, dual commentaries, or a wired mic connected to input 1 for at-computer use and a wireless mic connected to input 2 for away use, which I do). We need a fifth option, where it downmixes without any gain reduction.

 

[Thebigcheese]

I know this thread is nearly a year old by now, but I just want to add that there are scenarios where none of those options work (for example, singing with a guitar connected to the other input, dual commentaries, or a wired mic connected to input 1 for at-computer use and a wireless mic connected to input 2 for away use, which I do). We need a fifth option, where it downmixes without any gain reduction.

That is exactly what my proposal is for. Choosing just one side of a "stereo" source without any gain reduction.

 

[AaronD]

Just now seeing this thread. And I just recently finished copying (by hand) the electrical schematics from the field service manual of a professional analog mixing console (Allen & Heath GL3300) from what feels like AutoCAD to an actual electronic design program (KiCAD).

Anyway, I'm fascinated by the clever way that they solved this exact problem in their stereo channel strips. Two latching push-buttons, one labelled "MONO L" and the other "MONO R":

• Both up, results in unchanged stereo.
• One down and the other up, results in the up one removed and the down one copied to both sides.
• Both down, results in passive resistor-mixed mono that is copied to both sides.
  • Passive resistor-mixing gives the *average* of all inputs, not the sum, which is exactly what is needed here. The difference, as noted in previous posts, is 6dB for two equally-weighted inputs. Otherwise, the functions are identical.

The cleverness comes in the way that analog electronics behave, so it doesn't translate directly to software, but it does create a rather intuitive user interface in my opinion.

Here's my redrawn schematic of that section, in case anyone is interested:

Yes, the inputs are swapped as drawn. That's not a typo. And yes, the switch labels are also correct. The one labelled "L" actually controls the right channel, and vice-versa, but the end result is per the labels.
The four capacitors and the four resistors to GND are irrelevant for the function. They just account for some of the annoyances of an actual physical circuit with real-world parts.

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By the way, this is very early in the channel strip:

• Mic preamps
• Dual inserts (separate per side)
• This bit here
• Stereo EQ
• Pre-fade auxiliary sends (mixed to mono regardless)
• Stereo fader
• Post-fade AUX sends (also mono regardless)
• Stereo balance
• Submix selection (roughly "Tracks" in OBS)

Note also how late in the chain the balance/pan control is. That's standard for professional workflows. OBS has it right up front, which IMO is just wrong.

That wrong position does allow a trick for 2-channel mic interfaces, where you have two copies of it, MONO both, and pan them to opposite extremes, to end up with a separate fader for each mic in OBS. But that trick is no longer necessary with this new MONO function. So please also put the pan/balance at the END of the chain, post-everything, where it belongs.