I have an audio input plugged into my mic jack. In alsamixer, when I unmute and amplify the mic input, I can hear this audio out of my speakers. However, running arecord -d 5 foo.wav and aplay foo.wav results in an empty file; the same when recording through audacity - empty.

Why does this happen? How do I record this input?

arecord -L produces the following, if this is helpful:

default

    Playback/recording through the PulseAudio sound server

pulse

    Playback/recording through the PulseAudio sound server

front:CARD=nForce2,DEV=0

    NVidia nForce2, NVidia nForce2

    Front speakers

surround40:CARD=nForce2,DEV=0

    NVidia nForce2, NVidia nForce2

    4.0 Surround output to Front and Rear speakers

surround41:CARD=nForce2,DEV=0

    NVidia nForce2, NVidia nForce2

    4.1 Surround output to Front, Rear and Subwoofer speakers

surround50:CARD=nForce2,DEV=0

    NVidia nForce2, NVidia nForce2

    5.0 Surround output to Front, Center and Rear speakers

surround51:CARD=nForce2,DEV=0

    NVidia nForce2, NVidia nForce2

    5.1 Surround output to Front, Center, Rear and Subwoofer speakers

surround71:CARD=nForce2,DEV=0

    NVidia nForce2, NVidia nForce2

    7.1 Surround output to Front, Center, Side, Rear and Woofer speakers

dmix:CARD=nForce2,DEV=0

    NVidia nForce2, NVidia nForce2

    Direct sample mixing device

dmix:CARD=nForce2,DEV=1

    NVidia nForce2, NVidia nForce2 - MIC ADC

    Direct sample mixing device

dsnoop:CARD=nForce2,DEV=0

    NVidia nForce2, NVidia nForce2

    Direct sample snooping device

dsnoop:CARD=nForce2,DEV=1

    NVidia nForce2, NVidia nForce2 - MIC ADC

    Direct sample snooping device

hw:CARD=nForce2,DEV=0

    NVidia nForce2, NVidia nForce2

    Direct hardware device without any conversions

hw:CARD=nForce2,DEV=1

    NVidia nForce2, NVidia nForce2 - MIC ADC

    Direct hardware device without any conversions

plughw:CARD=nForce2,DEV=0

    NVidia nForce2, NVidia nForce2

    Hardware device with all software conversions

plughw:CARD=nForce2,DEV=1

    NVidia nForce2, NVidia nForce2 - MIC ADC

    Hardware device with all software conversions

Changes made on the Input tab of the System Settings -> Sound dialog make no difference at all. No sound comes out of my speakers because of them, and Audacity records nothing as a result of changing any setting (either the connector or the input volume). There is only one "device for sound input" - the Internal Audio Analog Stereo.

Oddly, in Audacity, changing the recording source (say from default:Line:0 to default:Mic:0, or even Mono to Stereo) sets the mute checkbox on the aforementioned dialog.