A new version video of drum record using midi overdub. As everybody knows - Ardour has no overdub midi function at this time (v.6.9), but there’s some workaround (Looks complicated, but after some practice the stuff goes fast):
- Add a midi track with the desired instrument.
- Add an empty midi track and connect its OUT to the IN of the instrument’s track.
- Activate a record mode for the empty track.
- Now, if you will enable your midi keyboard (or virtual keyboard, as it is shown in the video) - you can record the first layer of the midi clip in the empty track, but can hear the instrument (because of the connection between the empty and instrument’s track).
- When your record is finished - you can drag the freshly baked clip in to an instrument track and activate Loop Playing. During this you can hear the recorded clip & train your next layer sounds.
- Now, after you’ve found your sounds and rhythms - you’re ready to record the next layer to an empty track
- etc///
EDIT!!! :
People, big sorry - I’ve over-complicated the task! 
For a new layer record you don’t need any “empty” additional track. Just activate Record for the desired track and record a new layer - you will hear all the sounds from the previous layers simultaneously!! While nobody corrected me - here’s my corrected video:
(maybe I’ll delete this topic later and make a “new simple way ardour recording video”) Sorry again! 
