When an audio signal is inverted the sound wave is essentially flipped upside-down. The wave's positive peaks become negative and its negative peaks become positive. Many audio recording and editing applications, such as Audacity and Goldwave, come with a built-in sound wave "Invert" effects tool. The current GarageBand release, GarageBand 11, does not feature an audio signal inversion tool. To invert a track in GarageBand, you must install a third-party Audio Unit plug-in that can perform this task.
Step 1
Download an AU plug-in that features a phase-invert tool such as Sonalksis freeG channel strip AU plug-in. Save the plug-in to your desktop.
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Step 2
Click the "Finder" icon in the dock to open a new "Finder" window. Browse to "Macintosh HD," "Library," "Audio," "Plug-ins" then "Components." Drag the AU plug-in from the desktop to the "Components" folder.
Step 3
Launch GarageBand. If the application is already open, close it and re-launch it. Open the project you want to edit.
Step 4
Double-click the header of the track that contains the sound wave you want to invert. The Track Info pane will open on the right.
Step 5
Go to the "Edit" tab in the Track Info pane. Click on "Click here to add an effect." Scroll down to the "Audio Units Effects" section. Select the AU plug-in you installed in Steps 1 and 2.
Step 6
Click the AU plug-in's designated phase inversion button to invert the track. With the freeG plug-in, for example, the button is labeled "Flip." Click "Apply."
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