You can use the quantize note timing feature within the track editor window to correct the timing of your recorded software notes if they are off from the tempo. Quantizing will automatically snap the notes to the correct beat on the timeline grid.
Track Editor
First select the track you want to work with and open the track editor window by clicking on theTrack Editor button. It will automatically take you to the Notes view.
Select Notes
Select one, several or all of the notes that you want to edit. If you don't select any notes, GarageBand will automatically edit all of them.
Quantize Note Timing
Go to the Quantize Note Timing bar on the bottom left of the sidebar and click on the arrow. Scroll through the note options and select one that is most similar to the notes on your grid. Your notes will snap to the closest note value on the grid.
Make sure you choose the correct note type. If it is far from your grid notes, it could make a drastic shift and change your melody.
