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This button looks like a black Apple icon in the upper-left corner of your screen. It will open a drop-down menu. This will open your System Preferences in a new window. This option looks like a speaker icon on the System Preferences menu. It will open your computer's audio settings. This button is located next to Sound Effects and Output at the top of the Sound window. You'll see a list of all the audio input devices connected to your computer here. Find the microphone you're using, and click on its name. This will boost the selected microphone's audio input to a higher level of volume. You can now speak to your microphone, and check the Input level indicator here in order to see if your microphone's input is boosted.
Click the Apple icon on your menu bar. Click System Preferences on the menu. Click Sound in System Preferences. Click the Input tab. Select your microphone on the Input menu. Slide the Input volume slider to the right.