Enabling Arm on Selection in Ableton
Arm on Selection in Ableton allows you to automatically arm the track as soon as it is selected. This option is not enabled by default in Ableton, and requires you to place a text file in the Ableton folder.
The above mentioned folders can be found here
Mac OS X:
Create an Options.txt file
In the text file, add this text
Once you save the file in the folder, restart Ableton. After arming the first track, you will notice that selecting a different track automatically arms it.
Sending Note On messages seem to trigger Ableton functions twice
You need to send a Note On message and then a Note Off message. Sending only a Note On message will cause this issue. Alternatively, use CC messages instead.
MIDI Settings in Ableton
Only the Remote setting for the MIDI IN port needs to be selected in Ableton