| Nononono guys!
With double thumbing you don't just slap "downstrokes" but also do upstrokes with the thumb, quite similar to how a pick is used.
You strike the string with the (side of the tip of your) thumb, "move through" that string and let the adjacent string stop the motion. Then move the thumb up in the same way.
You can combine this with a pop to get a triplet, for example: slap-down, slap-up, pop.
Check out Victor Wooten or Alain Caron for examples.
You should do this with quite a light touch, most problems occur in the beginning when you do it too hard IME.
Good luck.
__________________ "El sueno de la razon produce monstruos." "The sleep of reason brings forth monsters."
Francisco
Goya |