Sound Preferences on Your MacBook
The Sound preferences pane of the Hardware section of the System Preferences window is where you can set the audio volume and mute sound. To set the overall system audio volume, drag the Output Volume slider. To mute all sound from your MacBook, select the Mute check box. Select the Show Volume in Menu Bar check box, which displays a convenient volume slider menu bar icon.
The three tabs here are
Sound Effects: From this pane, you can choose the system alert sound and the volume for alerts. You can also choose to mute application and Finder menu sound effects, as well as toggle the sample sound effect when the volume keys are pressed on your MacBook’s keyboard (or from the Volume slider).
Output: Use these settings to choose which audio controller your MacBook uses for playing sound. Unless you’ve installed additional audio hardware, this remains set to Built-in Audio or Internal Speakers. You can adjust the balance between the left and right channels for the selected output controller.
Input: These settings allow you to specify an input source. Unless your MacBook includes a Line In input source, leave this set to your Internal Microphone. Drag the Input Volume slider to increase or decrease the input signal volume; the input level display provides you with real-time sound levels.
If your MacBook is in a location with a large amount of background noise, click the Use Ambient Noise Reduction check box to improve the quality of your audio input.