On Sat, 2013-03-16 at 13:48 -0400, Doug wrote:
Your NVidia card has a sound decoder that feeds the HDMI output. If it's
like mine, there is no other sound output connection on it.
In Linux, I have had little to no success using that output; in XP, the
NVidia driver will send the output to your TV, while disabling the
normal sound device.
Most likely the issue is related to this. I've got an on-board ATI with
a HDMI thingy connected to an PCIe port, but I don't have experiences
with the on-board device and the HDMI thingy. On my machine all those
consumer devices are disabled.
Since there's no latency when the microphone is connected, but there's
audible output, it might be just hardware monitoring without an
connection to the software. OTOH I can't believe that a consumer
on-board device should provide hardware monitoring.
I wonder if it would be possible to record input from the mic by
"audacity" (ALSA or JACK) or if "meterbridge" (JACK) should show a
signal.