User tomreviewer shows us how to get autotune in GarageBand. Open GarageBand and create a new project. Make sure the Key is set to C. Delete the default track by clicking on Track, then Delete Track. Start a new track by clicking on Track, then New Track. Select Real Instrument Track when prompted and click Create. In the sidebar that opens click on Vocals, then Male Basic. Any of the Vocals, however, can be used. Press the Record button and record your voice. Click on the Scissors icon in the bottom left of the window. Under Enhance Tuning, move the slider all the way to the "max" setting and check the Limit to Key box. Your recording should now sound autotuned, just like T-Pain!