>>It makes sense when it works - I'd stay away from inserting a backloop into the sound card like this, because I suspected it would build feedback and possibly get fried. And even if I had an old sound card I'd be willing to sacrifice for the experiment, there's no telling whether a nasty trick like this would work on all cards. They could be wired in unpredictable ways.
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>Oh, right - positive feedback is quite dangerous. But: Do you really think that the sound that comes into the computer would go back out?

Well, that's what happens with line-in, right? You plug anything in, and you can listen to it going out. Though it's been a while since I last tried that, maybe a few motherboards ago. Anyway, I'm not the type of guy whose experience grows with the amount of magic smoke released from the circuits. I do software, not hardware :).