The device should be automatically recognized and listed in the columns at the top of the pane. If you do not see it there, disconnect from and reconnect to your Mac.
The Input level bar helps sound check your microphone. When the bar does not respond to your voice or to taps on the mic, you'll need to trouble-shoot your connection. Make sure you have not muted your mic. Many current-generation USB microphone solutions provide at least one, if not two, separate mute buttons. You'll usually find a mute toggle on the cord of the microphone or headset. Some USB solutions offer a second mute button on the dongle that connects to the USB port as well.
Most mic solutions are USB-based. For best performance, connect to a USB port directly on your Mac. The other day, I had a great deal of trouble setting up a voice chat with coblogger Dave Caolo until I switched my mic connector from an external hub to a built-in port. I could hear him; he could not hear me.
Once you have confirmed that you have live voice input as indicated by the Input level bar, make sure you've set up audio properly in your chat client. Both iChat and Skype offer input settings in their built-in preferences (App menu > Preferences, or Command-comma). Make sure that your new microphone has been selected in whichever chat program you use.
Always allow a little more time than you think is necessary to get a new microphone set up with your Mac. Take time to get the input set up and verified before making your first call. Once you've set up your mic the first time, it's generally smooth sailing from there on.
Other tips, courtesy of our readers:
- Option-click the volume control in the main menu toolbar to select input and output devices without opening up System Preferences.
- Some Microphones require power on the stereo mini jack and may not work on Mac systems. Try to check for Mac compatibility when buying USB microphone sets. Unamplified PC microphones often won't work.
- MacBook Pros are compatible with iPhone microphone-on-the-cord headphones. Just plug your headphones into the headphone jack, and the mic will be listed in your input sources (and your volume/play/pause controls will work if you have them)