Automation is the process of telling REAPER to remember changes that you want made to any of your track or plug-in parameter settings during the course of a song and to reproduce those changes in real time every time the song is played or when the project is rendered. Some simple examples of when you may wish to use automation include:
To fade up the volume on a particular instrument (or group of instruments) during a lead break
To adjust the EQ gain levels at one or more frequency settings to make the vocal appear more intimate during a particular line or phrase
To change the pan settings on one or more tracks to create the effect of live movement on stage
Automation can be applied to both MIDI tracks and items ...