To listen to sound (["Ogg"], ?"MP3", .au files, !["CDs"] etc) on your sound card, you need to:

You can install too eg [http://freshmeat.net/browse/113/?topic_id=113 Sound/Audio apps] or [http://www.underbit.com/products/mad/#using wiki:?MAD apps using], 'xfreecd' (music CD playing software), 'mp3blaster' (full-screen console mp3-player), or 'saytime' (if you have no CD drive and no !["MP3s"]). Try to run them as root (it should work). With Debian, ordinary users lack permission to read the CD drive and write to the audio device (usually /dev/dsp), and they probably can't use these programs (yet; see next paragraph).

ALSA loads sound 'cards' in the order it finds them. The first card is always used as the 'default'. If you're unlucky, and a microphone gets selected first, then you're not going to be able to play sounds. You can check the order that ALSA has loaded card with:

  cat /proc/asound/cards

There are two ways to fix this problem.

1. Force the cards to load in a different order. I chose this route, and added the following to my /etc/modprobe.d/sound:

  options snd-trident index=0
  options snd-usb-audio index=1

This forces my Trident card to be the default (card 0) and my USB microphone to be card 1.

2. Change the default card by editing /etc/asound.conf or ~/.asound.conf

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