Apple Logic Pro 7 - Manual (Page 317)

Chapter 7 Automation 317
Read
Read will automate the current track, using the existing automation data.
The data cannot be changed in realtime by touching/moving the fader.
Touch
Touch will automate the current track in the same fashion as Read.
Should the fader be touched, the existing Track Automation data of the current fader
type will be replaced by any new fader movements—while the fader is pressed/
touched. Touch is the most appropriate, “standard” mode, used for creating the mix. It
allows you to correct and improve the mix at any time, when automation is active. The
time required by a parameter to return to its previously recorded setting, is set via
Options > Track Automation > Track Automation Settings > Ramp Time (ms).
Latch
Latch basically works like Touch, but the current value will replace any existing
automation data, after releasing the fader—when Logic is in playback (or record)
mode.
To finish, or to end parameter editing, stop playback (or recording).
Write
In Write Mode, existing Track Automation data is erased as the Song Position Line
passes it.
If you move any of the Mixer’s controls, this movement will be recorded—if you don’t,
existing data passed by the SPL is simply deleted. Use Options > Track Automation >
Track Automation Settings to determine the type of data that should be erased. The
Write Mode changes to setting determines the mode that Logic switches to after a Write
operation has been executed.
Be careful with the Write mode (and its settings), to ensure that you don’t erase your
pan, bus, and EQ automation data by mistake, if your intention was only to erase
volume fader information!