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I would like to know whether it's possible to record sound from two different sources on a computer with a single stereo jack input (I'm not sure whether this is a "line in" or "mic" input).

Each microphone would be at most at about 6m (20ft) from the input jack, but possibly at different length (one could be 1m away from the computer and the other one at 6m). I don't have any specific microphone in mind at the moment, but they could be of different type.

Are there any problems I should expect? In particular, would soldering the two mono wires onto the same jack (sharing the same ground) cause any problem, or should there be a circuit ahead? If so, what kind of circuit?

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  • \$\begingroup\$ Generally anything that has a stereo input is expecting line level signals. So you will need a preamp before your mic. I am not sure this is the best place for this question though. The audio-video stackexchange might be a better fit. \$\endgroup\$ – Kellenjb Mar 23 '12 at 14:31
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    \$\begingroup\$ @Kellejb, thank you. Sorry, I thought this would be a better place, since I'd like to know what the issues are from an electronics perspective, and perhaps pointers to schematics if it's not too complex. (The fact that such devices may exist out of the box are of interest, of course.) \$\endgroup\$ – Bruno Mar 23 '12 at 14:37
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What you want to do should work, as long as your sound card really has stereo microphone inputs. Most will have stereo "line" inputs and at least some kind of microcphone input, but you need to check whether that mic input is stereo or not. If it is, just hook up the two mics to the common ground and the other side of each mic to one of the two input channels. Make sure to use shielded audio cable.

If you don't have a stereo mic input, then it would be better to use a separate preamp so that each signal is amplified to "line" level, then put the two line level signals into the line level input of the sound card. In that case you have to be very careful about ground loops since the preamp will be separately powered. Plug it in as close as possible to the same place the PC is plugged in to, and don't hook up a separate deliberate ground to it other than thru the line in connection of the sound card.

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Like Olin says, make sure to use shielded cable, or you'll pick up all kinds of noise. Shielded cable comes in different qualities. I've seen cable where the shielding consisted of strands loosely surrounding the central conductor. Make sure it's properly woven, you'll need it especially for the 6m cable.
Line inputs on a PC are always stereo, I guess microphone inputs are mono. You'll have to amplify the lower microphone levels with a pre-amplifier if you want to use line inputs. Place the pre-amp as close as possible to the microphones, so that the amplified signal travels the 6m. If you use a stereo cable for each microphone you can use the extra wire for the DC power supply.

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