I-Mic is a priceless little add-on for routing sound in/out from a standard mike into your pc or from you pc out to earphones or speakers. Makes the process a lot simpler than using the default sound jacks on the back of the pc, and it uses USB.

I have had good results using a more complex device, M-AUdio's Omnistudio, for providing multiple mike-in channels directly to Mac over Firewire. Works a champ but was a little pricey.

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