[ltp] Thinkpad X40 --- no line in jack?!

[Norman Ramsey]

 > On Sun, 26 Sep 2004 21:55:42 -0400 (EDT), Norman Ramsey
 > <nr@eecs.harvard.edu> wrote:
 > > I've just discovered that my newly purchased X40 has no line-in jack
 > > for audio input from my stereo.  (The salesman who told me that a single
 > > jack doubles as microphone and line in must have been crazy.)
 > 
 > He's not crazy.  many ports on newer sound cards do double or triple
 > duty.  One jack my provide not only line in but mic and even
 > rear-channel line out depending on what "mode" the chip is in.  I
 > think ALSA supports most of these situations via the mixer.

I would love to figure out how.  On my machine, alsamixer reports

  Card: Intel 82801DB-ICH4                                                     
  Chip: Analog Devices AD1981B                                                 

and there's a `mic select' that's suggestive, also an `external
amplifier' that can be turned on and off.  But I don't want to just
plug things in without knowing what's what, for fear of blowing my
sound card's little circuits.  Any idea where to look for
documentation? 


Norman