someone explain read, latch, and write

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That bad, huh?

(I guess you've found the answer?)

Ha ha!  No, not that bad.  The asterics are the original post... I know so little about read, latch, and write that I didn't know what to say.

[OFF]

Automation has 5 different modes:

1. OFF - ignores any of the automation parameters for that track
2. READ - process automation data for all parameters for that track.  During playback, each parameter that contains automation data is adjusted to match that data.
3. WRITE - overwrites any existing automation data under the playback cursor, unless that automation lane has been made "Safe During Write."  For example: You have manually click some Mute on/off points, and in Write mode, attempt to record some Volume fades.  If the playback section occurs where Mute nodes existed, they will be overwritten by whatever status Mute happens to be in at the time playback was started.  If you click the "Safe During Write" button on the Mute lane, this lane will act as if it were in READ mode while you are writing the Volume data.
4. LATCH - does not overwrite any existing automation data UNTIL you make a change to the parameter, at which point it "latches" on to the new value until you make additional changes or stop playback.  Upon stopping playback, it writes a final node and draws the envelope between that point and the next pre-existing node.  If no pre-existing nodes exist, the parameter remains at this level for the rest of the session.
5. TOUCH - does not overwrite any existing automation data UNTIL you make a change to the parameter, at which point it gradually moves back to the level it was at before the change was made.  For example: Track 1 Volume is set to +1dB with no automation data.  In touch mode, if I drop the volume to -3dB during playback, when I take my finger off the knob (or release the mouse button) the volume level will linearly rise back to 1dB.  (The time in which the return to the pre-existing parameter level occurs is modifiable.  Click Edit > Preferences > MultiTrack and edit the Automatch Time setting.  You can also modify the thinning parameters to reduce the number of edit point nodes captured per second.)

I hope that helps some.  Please let me know if you have additional questions as this is a pretty deep feature.

I hope that helps some.  

Enough to make the thread sticky...

It's a pity the help file's fairly brief (but clear) summary didn't go into that illustrative detail.

Yes it does indeed help. A very nice explanation for a great feature. I was planning on going to the manual for an explanation, but this explains it all nicely. Thank you.

It's a pity the help file's fairly brief (but clear) summary didn't go into that illustrative detail.

I agree.  The first thing I did when looking at these was read the help file entry, and that left me scratching my head.  I then re-read it very carefully and gradually figured it out.

That's the problem with help files in many products: they stick just to the facts where they would be much better served by some additional illustrative examples.  Too often I look to the help for some feature, and all that is there is a one-liner when a deeper explanation would be more useful.

I was playing today with automation (no control surface, just the mouse) and I cannot make Touch work as it is supposed to work. It works fine for Volume and Pan - when I release the mouse button, the knob or the mixer slider returns to the previously set position. But it works like Latch for added effects, like Amplify, Pitch Shifter, Tube-modelled Compressor, or Studio Reverb (these I tried). When I release the button, the slider stays where I left it until playback is stopped. Any ideas what could I be doing wrong? Or is this supposed to work this way?

It does work that way - whether it's supposed to is unclear.

I have not found the difference in Touch-ing volume or pan vs. other effects anywhere in the help file or manual. Looks like a bug, or someone decided not to admit in manuals that the feature is so limited.