I think this must be a quirk of the hardware: onboard Intel
82801BA-ICH2, chip AD1885
Jackd running, meterbridge connected to alsa_pcm:capture_1 and _2
Everything on alsamixer un-muted and faded up (except the 20db mic gain).
Signal plugged to the mic input appears both on the meters, and on the
h/p jack
Signal plugged to the line jack appears at the h/p jack, but not on the
meters.
I find this baffling.
Andrew.