Issue Connecting Monitors to Laptop While Recording
- Thread starter lrchance1
- Start date
deFrisselle
Member
Check your connections, make sure they are secure
The connections probably *are* secure. I think it's a ground loop.
With just the laptop, there's only one path to ground, through the laptop's power cord. That's fine, and needed for safety in case something goes wrong with the power supply that would otherwise make something user-accessible, live. If that were to happen, then the ground wire completes a short circuit from the now-live case or other user-accessible part, to the neutral bus that it's tied to in the electrical panel. That trips the breaker for that circuit. (which means the ground wire needs to be big enough that it *can* trip the breaker)
If you remove the ground pin, either by breaking it off or with an adapter, then you lose that safety. The case could become live, and then YOU become the short circuit! NEVER break a safety ground!
(Note: The adapter - in the U.S. at least - is meant to CREATE a ground, not to "just make things function", because the metal tab is supposed to connect to the screw of a 2-pin outlet, which is assumed to have a metal path back to the panel, usually in the form of a metal box and conduit.)
If the monitors are connected to a different ground, that perhaps takes a different path back to the panel, or might even go to a different panel if you have a series of retrofits or an otherwise weird setup, then they're still protected the same way, but that big loop of wire is also an antenna. When you plug in the signal cord, that completes the loop, and now everything gets an additional "wiggle", according to what that antenna picks up. Digital things are mostly immune to it, but analog things, like the raw mic, can't tell the difference.
Usually, the strongest of those unwanted "signals" comes from the AC power line. 50Hz or 60Hz, depending on where you live, plus a bunch of harmonics because few things draw power evenly and their noise gets added as well. This appears as a buzz in analog audio gear (you hear the harmonics better than the fundamental), and a horizontal bar in analog video gear that may or may not wander up and down (video signals were originally locked to the AC power frequency, and haven't changed much since).
That said, I've also had a ground loop pick up an internal switching power supply, instead of the raw AC power line. It was a "warble" instead of a "buzz", that changed with even the slightest change in CPU load. Even moving the mouse was enough to affect it. Unplugging the laptop from the wall - running on battery - fixed it, and plugging it back in brought it back. Yep! Classic ground loop, even though the sound is different from what it usually is.
Regardless though, the general solution is the same: break or minimize the loop antenna that is formed by the different ground paths. As before, NEVER break a safety ground! Which means that you can't rely on the signal cord to provide the safety path either. It may fry and break, *without* tripping the breaker.
So the practical solution, then, is to either isolate the signal, using a transformer for analog audio (same principle as a power transformer, but with different dimensions and materials), or a specifically-designed isolator for whatever signal you're using (I fixed the "warble" above with a USB isolator); or move everything to the same power strip that is big enough to handle it all. Don't cascade strips. The latter is probably much easier for you. If it's still a problem, then you're probably looking at a video signal isolator for each monitor.