Analog audio is not analog audio. And 1/4" TRS is the universal confuser because it's used for practically everything regardless of compatibility.
- Balanced Mono:
- Tip = + or "Hot"
- Ring = - or "Cold"
- Sleeve = Ground
- Unbalanced Stereo:
- Tip = Left
- Ring = Right
- Sleeve = Ground
- Unbalanced Insert, for completeness:
- Tip = Send
- Ring = Return
- Sleeve = Ground
When you adapt from XLR to TRS, you get:
- XLR pin 1 = Shield (X), or Ground -> TRS Sleeve
- XLR pin 2 = Live (L) -> TRS Tip
- XLR pin 3 = Return (R) -> TRS Ring
- Note: "Return" in this sense is an electrical *circuit* return, not a signal return. Imagine it driving a transformer or light bulb between pins 2 and 3...
No change in format, only a different connector.
When you then put that into a TRS jack for a stereo line-in, you get:
- Ground -> Ground (so far so good)
- Hot -> Left
- Cold -> Right
Now to see what that actually does, we have to look at *how* the source is balanced:
- Impedance balanced:
- Signal -> resistor -> Hot (the primary job of that resistor is to prevent the driver from self-oscillating into a long cable)
- Ground -> resistor -> Cold (the primary job of *that* resistor is to match the other one, which allows equal pickup of noise)
- Ground -> Ground
- An important point to make here is that the entire point of a balanced line is to reject noise. Equal pickup on two wires means that they can be subtracted and the *difference* taken as the intended signal. ANY difference will do, and impedance balancing is enough to provide that. If the sending circuit happens to end up with an inverted signal and the receiving end is guaranteed to be balanced, just drive the Cold line with that inverted signal, and tie the Hot to ground. Free inversion! The polarity-reverse button on an analog console also simply swaps the two balanced wires.
- Signal balanced:
- Signal -> resistor -> Hot (same as before)
- Inverted Signal -> resistor -> Cold
- Ground -> Ground
- This provides twice the voltage swing compared to impedance balancing (remember we're looking at the *difference* between Hot and Cold), but requires an explicit inversion. Practically, it's two independent line outputs that always do opposite of each other.
- Floating balanced:
- Same as Signal balanced, except that the average is not fixed at 0. Either wire can be tied to ground, and the entire signal appears on the other wire in its respective polarity. Or the "common mode", as it's called, could be ground loop noise, or whatever else. As long as you leave enough headroom to keep the total of everything between the power rails, this effectively simulates an isolated transformer output without an expensive transformer. (note: ground loop isolators are transformers too)
If you wiring-convert that to what the system now thinks is stereo, just because of the jack that you plugged it into, you get:
- Impedance balanced:
- Hot = Signal -> Left
- Cold = Silence -> Right
- Signal balanced:
- Hot = Signal -> Left
- Cold = inverted Signal -> Right (you can't hear the inversion, so it sounds "okay" so far)
- Floating balanced:
- Possibly wandering stereo pan, where Right is always inverted, but again, you can't hear the inversion.
If you mix *that* to mono, like for a single speaker on a phone, you get:
- Impedance balanced:
- Signal + Silence = Signal
- Signal balanced:
- Signal + (-Signal) = Signal - Signal = Silence
- Floating balanced:
- Possibly wandering in and out
Based on your description, the balanced output from your board is either Signal balanced or Floating balanced. If it's Floating, then the load on each wire just happens to be similar enough to give a similar volume on each one. For a balanced mono input, it's important to make that true for equal noise pickup and thus rejection, but for unbalanced inputs like your stereo line-in, it's not guaranteed.
When you had the single RCA, you forced it to Unbalanced Mono and then split *that* back out to what the system thought was stereo. So everyone got the same thing. Now, you still have the same effect in headphones, but the Right channel is inverted, so a perfect mix of *that* becomes silence. Two speakers close to each other in free air will give you something in between, possibly weird at times depending on the acoustics of the room where those speakers are.
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This has nothing to do with the computer or OBS, and everything to do with how you feed the computer.
