如何使用外部USB声卡并将其设置为默认值？

 # Check ALSA modules
cat /proc/asound/modules

 0 snd_bcm2835
 1 snd_usb_audio

# Check sound hardware
cat /proc/asound/cards

 0 [ALSA           ]: bcm2835 - bcm2835 ALSA
                      bcm2835 ALSA
 1 [Set            ]: USB-Audio - C-Media USB Headphone Set
                      C-Media USB Headphone Set at usb-3f980000.usb-1.5, full speed

# Check info on card-1
amixer -c 1

Simple mixer control 'Headphone',0
  Capabilities: pvolume pswitch pswitch-joined
  Playback channels: Front Left - Front Right
  Limits: Playback 0 - 151
  Mono:
  Front Left: Playback 104 [69%] [-8.88dB] [on]
  Front Right: Playback 104 [69%] [-8.88dB] [on]
Simple mixer control 'Mic',0
  Capabilities: pvolume pvolume-joined cvolume cvolume-joined pswitch pswitch-joined cswitch cswitch-joined
  Playback channels: Mono
  Capture channels: Mono
  Limits: Playback 0 - 32 Capture 0 - 16
  Mono: Playback 23 [72%] [34.36dB] [off] Capture 0 [0%] [0.00dB] [on]
Simple mixer control 'Auto Gain Control',0
  Capabilities: pswitch pswitch-joined
  Playback channels: Mono
  Mono: Playback [on]
 

 sudo apt-get remove pulseaudio

# You can keep `jack*`, but make sure it is not running.
# If it is running you need to stop it, disble it or remove it.
service --status-all
# Disable the running service with:
sudo systemctl disable xxxxx
 

 # Edit boot config with:
sudo nano /boot/config.txt
# so that:
cat /boot/config.txt
...
# Enable audio (loads snd_bcm2835)
#dtparam=audio=on
dtparam=audio=off
...
# You need to reboot!
sudo reboot now
 

 cd /etc/modprobe.d/
# Manually edit a new file:  blacklist-snd_bcm2835.conf
#sudo nano blacklist-snd_bcm2835.conf
# And add the line: blacklist snd_bcm2835
## OR directly with:
sudo tee /etc/modprobe.d/blacklist-snd_bcm2835.conf <<EOF
blacklist snd_bcm2835
EOF
# You need to reboot!
sudo reboot now
 

 $ cat /proc/asound/modules
 1 snd_usb_audio

$ cat /proc/asound/cards
 1 [Set            ]: USB-Audio - C-Media USB Headphone Set
                      C-Media USB Headphone Set at usb-3f980000.usb-1.5, full speed
 

 #cat ~/.asoundrc
cat << EOF | tee ~/.asoundrc

pcm.!default {
        type hw
        card 1
}

ctl.!default {
        type hw
        card 1
}
EOF
 

 sudo nano /usr/share/alsa/alsa.conf
# then replace:
#defaults.ctl.card 0
#defaults.pcm.card 0
# with:
defaults.ctl.card 1
defaults.pcm.card 1
 

 # Check with:
vcgencmd codec_enabled MPG2
vcgencmd codec_enabled WVC1
 

 # get some demo sound and video files
cd ~/Music

wget -Lk http://rpf.io/lamp3 -O example_11k.mp3
wget -Lk http://www.kozco.com/tech/piano2-CoolEdit.mp3 -O pianoTest_48k.mp3
wget -Lk http://www.sample-videos.com/video/mp4/720/big_buck_bunny_720p_2mb.mp4 -O bbb_720p_2mb.mp4
wget -Lk https://raw.githubusercontent.com/mediaelement/mediaelement-files/master/big_buck_bunny.mp4 -O bbb_360_22k.mp4
 

 # Double-check! 
aplay -l && arecord -l

**** List of PLAYBACK Hardware Devices ****
card 1: Set [C-Media USB Headphone Set], device 0: USB Audio [USB Audio]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

**** List of CAPTURE Hardware Devices ****
card 1: Set [C-Media USB Headphone Set], device 0: USB Audio [USB Audio]
  Subdevices: 1/1
  Subdevice #0: subdevice #0


# Play white noise on 2-channels (L/R) on Card-1 
speaker-test -c2 -D hw:1,0

# Play a WAV sound file
speaker-test -c2 -D hw:1,0 --test=wav -w /usr/share/sounds/alsa/Front_Center.wav

# Once the correct default card+device is set, and after reboot, 
# then full left/right voice test (above) is performed, just by:
speaker-test -c2 -twav

# Record some sounds (with a VU bar):
arecord --device=hw:1,0 --format S16_LE --rate 44100 -c1 -V mono test.wav

# Play recorded sounds
aplay -D plughw:1,0 test.wav

# Play recorded sounds (sample rate have to be equal) 
speaker-test -c2 -D plughw:1,0 -r 44100 --test=wav -W $HOME -w test.wav

# Install an MP3 player
sudo apt-get install mpg123

# Play some MP3 file
mpg123 -v -r 44100 some.mp3

# Play an MP3 sound stream
mpg123 http://ice1.somafm.com/u80s-128-mp3


# This plays video, but no sound!
omxplayer -o alsa /opt/vc/src/hello_pi/hello_video/test.h264

# This plays video and sound!
omxplayer -o alsa bbb_720p_2mb.mp4

# The following plays sometimes (!?) and at the wrong speed!
omxplayer -o alsa some.mp3