I'm running a mic into a small mixing board, and then taking the signal from the headphone jack on the board and running it into a laptop. Well, specifically, the mic port on the docking bay of the laptop.

When I listen to the signal coming from the mixing board on my headphones, it sounds fine. When I run an MP3s player directly into the mic port on the dock, it records fine too.

But when I run the phones jack to the mic input, the recording is awful. I don't even get a signal.

What could cause that?

We've tried playing with the mic levels. Tonight, the whole IT department tried to isolate the problem and fix it, but we don't have a lot of audio equipment to test with. Still, no luck. Thoughts?

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    awful and no signal are very different things in my understanding. can you please clarify what exactly yo mean by that? – Eugene S Jul 8 '16 at 6:20
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    Stereo to mono, ground loop, mismatched impedances... the list goes on. Don't mix line level & mic level, they don't fit. – Tetsujin Jul 8 '16 at 8:36
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    Like @Tetsujin said, this is a bad idea, but I've done stupider things in the past. On this occasion, it's a fail for numerous possible reasons! Check this thread on the subject for more details: arstechnica.com/civis/viewtopic.php?t=128977 – Marc W Jul 8 '16 at 14:08
  • We plug speakers into the phones jack coming from the mixer and it sounds beautiful. We can send audio from my cell phone into the computer's mic jack and it sounds fine. But when we send the phones jack to the mic jack, there's a loud buzz and a faint signal. High signal-to-noise ratio. Is there any way we could adapt line and mic level? @EugeneS – Slothario Jul 8 '16 at 20:08
  • Slothario - don't use mic in. You need line in. – Rory Alsop Jul 8 '16 at 20:16

Turns out the issue wasn't mic or line levels, but ground loop hum.

We were kind of limited by the hardware available. All we had were laptop docking ports with one junky mic in port. We were able to fix the problem by buying a computer and sending the phones to the line in/mic port. My (admittedly amateur) theory is that the laptop wasn't grounded like everything else was, and the PC had actual grounding in the common ground.

Or maybe the PC's sound card just had better hardware. Hmm.

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