If you want to auto-tune your voice to make it sound better you first need to decide if you actually need an Auto-tune. You may just be looking for a talk box or vocoder. An auto-tune makes your voice auto-tuned and sets it to sound much better. A vocoder only makes your voice computerized while the auto-tune actually changes the sound of your voice and tone of it. You can adjust your auto-tune and turn it up very high or lower it. You can auto-tune on Garage band. First, open up Garage band. First you will want to record a track or recording and put this recording on auto-tune. Double click on your track and open up the edit menu. On the option of enhance tuning, slide it over to 100%. Make sure the limit to key button is checked. Now, anything that has been highlighted in that track will now be auto-tuned.