Open your GarageBand song. Click the small headphones icon underneath your vocal track name. This allows you to listen to only this track without the others.
Double-click your vocal track to open the "Track Info" pane, then click "Real Instruments." This shows different types of effects that can be applied to any instrument.
Click the "Vocals" section to see a list of special effects that you can add to your vocals. Double-click any effect that you would like to use. Play the vocals back by clicking the "Play" button at the bottom of the screen.
Click the "Edit" tab to add effect plug-ins to your vocals. You will see the compressor and Noise Gate plug-ins. Click the small LED light next to the plug-ins so that you can hear them.
Click the the compressor plug-in to adjust it yourself, or select a preset from the drop-down menu. Compression enhances audio by packing in the signal so it is louder and clearer. The compressor includes sliders for attack, release, ratio and threshold. Attack sets the time to start the compression after it has risen above the threshold, and release sets how long it takes to stop the compression after it is below the threshold. The compression ratio determines how much compression is used. Set the ratio to 2:1 for milder compression and 6:1 for stronger compression. The threshold is the volume level where the compression begins. Use the gain control to compensate for the volume loss during the compression process.
Go to the Noise Gate plug-in and adjust the gate level by moving the slider. This effect removes any sounds below a certain level. This gets rid of sounds like clicking, breathing or any background noise. It is recommended to keep this at a low level because setting it too high may make your voice too quiet or remove it altogether. Use this after applying compression to your vocals because it increases the noise level and brings out the quiet sounds in the recording.
Click the small LED light next to the effects and click the "Play" button at the bottom of the screen to listen to your vocals. You will hear how your vocals sound with each of the effects applied to it. Click "Save Instrument" at the bottom of the "Track Info" pane. Your vocals have been enhanced.