user "pip" explained it to me like this:
The Trigger Finger can send a note on/off message when a pad is hit (with note's velocity being the speed it was hit) in addition to a CC message for the aftertouch pressure.
By default, all of the presets for your trigger finger will either:
1. Send no aftertouch data
2. Send the same CC value for ALL pads.
3. Preset 15 sends a different CC for each of half of the pads, and no CC for the other half. Confusing.
[factory presets 10,11,12 and half of 15 send aftertouch data. RTM if you're curious about specifics.]
If you use M-Audio Enigma [free download. aggravating software to use.] you can send a different CC for each pad.
When you midi-learn in live, hit the "Ctrl/Note Mute" button until it says "Not". This temporarily disables the note message, so you can assign your beat grid to the pressure of the pad. After you're done midi-learning, hit the "Ctrl/Note Mute" button again until its LED turns off.
The behavior of the pad will now change the size of the beat grid as you lean on the pad, which is half of the solution to your question. If you want the beat grid to be the size of the velocity that you STRIKE the pad and not LEAN on it, you'll need some Midiox and Midiyoke mojo:
You'll need to set midi-ox to convert "note on" velocity to a CC value. In midi-ox go to Options > Data Mapping and do it in there. Then go to View>Port Routings and take your Trigger Finger's input and route it to a midi-yoke port. Back in Live, go to Options>Preferences and disable your trigger finger, and use the midi yoke port instead!
I know the instructions are rather vague, let me know if you need me to clarify anything specific or if you've just decided that this is too much work
--Pip
(from this post -
http://www.ableton.com/forum/viewtopic. ... highlight=)