Attach your usb sound card and see what your kernel says:
# dmesg | tail
[ 874.802892] usb 3-1: New USB device found, idVendor=0763, idProduct=2010
[ 874.802900] usb 3-: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[ 874.802907] usb 3-1: Product: Fast Track
[ 874.802911] usb 3-1: Manufacturer: M-Audio
[ 874.803093] usb 3-1: configuration #1 chosen from 1 choice
[ 875.442986] usbcore: registered new interface driver snd-usb-audio
Ok, you debian machine has recognized correctly your sound card. Make sure your snd-usb-audio module is loaded correctly
# modprobe snd-usb-audio
Now using aplay we can list out playback devices:
# aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: Intel [HDA Intel], device 0: ALC262 Analog [ALC262 Analog]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 1: HDMI [HDA ATI HDMI], device 3: ATI HDMI [ATI HDMI]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 2: Track [Fast Track], device 0: USB Audio [USB Audio]
Subdevices: 1/1
Subdevice #0: subdevice #0
As you can see card 2 is my usb audio card.
If your usb sound card comes with a microphone, you should test if the capture device is working correcty: use arecord for this test,
# arecord -l
**** List of CAPTURE Hardware Devices ****
card 0: Intel [HDA Intel], device 0: ALC262 Analog [ALC262 Analog]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 2: Track [Fast Track], device 0: USB Audio [USB Audio]
Subdevices: 1/1
Subdevice #0: subdevice #0
Yep! Looks like card 2 should be able to register my voice. But before testing if everything is working correctly, check your card's volume using alsamixer:
# alsamixer -c 2 -V all
In alsamixer the -c parameter is used to select what card do want to manage and the -V all isused to display all cards volumes.
Finally we can make a simple test by recording your voice and playing out.
To record:
#arecord -d 10 --device=hw:2,0 -f cd -t wav /tmp/tmp.wav
and to playback
# aplay --device hw:2,0 /tmp/card2.wav
Playing WAVE '/tmp/card2.wav' : Signed 16 bit Little Endian, Rate 44100 Hz, Stereo
Make sure you are testing the correct card through the parameter --device=hw:2,0.
hw: 2,0 means that you are using the Card 2 and the device 0: card 2: Track [Fast Track], device 0: USB Audio [USB Audio]