Video: What's the difference between Microphones?
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Omnidirectional, Cardioid, Hypercardioid, Bi-directional, Shotgun? What makes these different types of microphones unique? The best way to discover the differences is to go out and experiment yourself. But for those that don't have access to all of these different mics (and the free time), the next best thing is to let Ty Ford explain it to you. In this video (28MB MP4)Ty lets you see and hear the differences between several different mics. He also shows where the best placement would be.
That's what he gets for hosting useful info on a .Mac site though. 