External C-Media USB speakers on Ubuntu 11.10

I have a small-but-spiffy set of USB speakers, handy for travel. Here's how I got them to work.

First of all, there are a *lot* of moving pieces, and eliminating many potential sources of the problem (no sound emerges from the speakers) is critical to success.

For example, the speakers work on another system, so they aren't broken.

Other USB devices work in the port, so there's not a hardware defect.

Sound in general works on the laptop.

dmesg shows the speakers recognized appropriately when plugged in:

$ dmesg
[245788.608422] usb 1-1: ath9k_htc: USB layer initialized
[245789.124045] usb 3-1: new full speed USB device number 7 using ohci_hcd
[245789.261042] ADDRCONF(NETDEV_UP): wlan1: link is not ready
[245789.331223] input: C-Media USB Headphone Set   as /devices/pci0000:00/0000:00:13.1/usb3/3-1/3-1:1.3/input/input11
[245789.331380] generic-usb 0003:0D8C:000C.0003: input,hidraw0: USB HID v1.00 Device [C-Media USB Headphone Set  ] on usb-0000:00:13.1-1/input3

( If the hardware were not recognized, that would be a driver [kernel module] issue)

alsa shows the hardware properly recognized and configured. Alsa also creates a GUI mixer for the USB "card" when it's plugged in:

$ aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: SB [HDA ATI SB], device 0: ALC272X Analog [ALC272X Analog]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: Set [C-Media USB Headphone Set], device 0: USB Audio [USB Audio]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

Pulseaudio offers a good clue. It shows the USB card, but there is no sink for the USB card's output. Aha!

$ pacmd list-cards
Welcome to PulseAudio! Use "help" for usage information.
>>> 2 card(s) available.
    index: 0
 name: 
 driver: 
 owner module: 4
 properties:
               # It's the onboard audio
               # ...
 active profile: 
 sinks:
  alsa_output.pci-0000_00_14.2.analog-stereo/#0: Internal Audio Analog Stereo
 sources:
  alsa_output.pci-0000_00_14.2.analog-stereo.monitor/#0: Monitor of Internal Audio Analog Stereo
               # ...
    index: 7
 name: 
 driver: 
 owner module: 35
 properties:
  alsa.card = "1"
  alsa.card_name = "C-Media USB Headphone Set"
  alsa.long_card_name = "C-Media USB Headphone Set at usb-0000:00:13.1-1, full speed"
  alsa.driver_name = "snd_usb_audio"
  device.bus_path = "pci-0000:00:13.1-usb-0:1:1.0"
  sysfs.path = "/devices/pci0000:00/0000:00:13.1/usb3/3-1/3-1:1.0/sound/card1"
  udev.id = "usb-0d8c_C-Media_USB_Headphone_Set-00-Set"
  device.bus = "usb"
  device.vendor.id = "0d8c"
  device.vendor.name = "C-Media Electronics, Inc."
  device.product.id = "000c"
  device.product.name = "Audio Adapter"
  device.serial = "0d8c_C-Media_USB_Headphone_Set"
  device.form_factor = "headphone"
  device.string = "1"
  device.description = "Audio Adapter"
  module-udev-detect.discovered = "1"
  device.icon_name = "audio-headphones-usb"
 profiles:
  output:analog-stereo: Analog Stereo Output (priority 6000)
  output:analog-stereo+input:analog-mono: Analog Stereo Output + Analog Mono Input (priority 6001)
  input:analog-mono: Analog Mono Input (priority 1)
  off: Off (priority 0)
 active profile: 
 ports:
  analog-output-speaker: Analog Speakers (priority 10000, available: unknown)
  analog-input-microphone: Analog Microphone (priority 8700, available: unknown)

                # See? No output sink. 

There is probably a way out of this using output profiles, but I don't understand those yet. Instead, what appears to be needed is a udev rule that creates an output sink for the USB card, then redirects the default stream to use the USB card.

Upon plugging in the USB speakers, that udev rule should make the speakers the default sound device. Upon unplugging the speakers, the card and sink's disappearance will automatically force Pulseaudio to reroute the stream defaults to the onboard audio card and speakers.

Figure out the Pulseaudio index number of the USB card:

$ pacmd list-cards \
   | grep 'alsa.card_name = "C-Media USB Headphone Set"' --before-context=6 \
   | grep index \
   | cut -d' ' -f6

7

Figure out the alsa hardware number:

$ aplay -l | grep C-Media | cut -d' ' -f2 | cut -d: -f1

1

Add an alsa sink for the USB Card:

$ pacmd load-module module-alsa-sink device=hw:1,0

Figure out the Pulseaudio index number of the new alsa sink:

$ pacmd list-sinks | grep 'alsa.card_name = "C-Media USB Headphone Set"' --before-context=37 | grep index | cut -d' ' -f6

2

Change the default to the new sink

$ pacmd set-default-sink 2

Since the USB speakers are MUCH LOUDER than the onboard speakers, start them at a much lower level!

amixer -c 1 sset "Speaker" 5

So the final script should look something like:

#!/bin/sh
# This script makes the C-Media external USB speakers the
# default audio output. It should be run by udev.

# Figure out the Pulseaudio index number of the USB card
card_index=$( pacmd list-cards \
              | grep 'alsa.card_name = "C-Media USB Headphone Set"' \
              --before-context=6 | grep index | cut -d' ' -f6 )
echo "The USB card index is $card_index"

# Figure out the alsa hardware number
alsa_hardware=$( aplay -l | grep C-Media | cut -d' ' -f2 | cut -d: -f1 )
echo "The alsa hardware number is $alsa_hardware"

# Test if a USB sink already exists. If not, create one
if [ $( pacmd list-sinks | grep -q C-Media ) ]; then
   # Add an alsa sink for the USB Card
   pacmd load-module module-alsa-sink device=hw:${alsa_hardware},0
   echo "New alsa sink added"
fi

# Figure out the Pulseaudio index number of the alsa sink
alsa_sink_index=$( pacmd list-sinks \
                  | grep 'alsa.card_name = "C-Media USB Headphone Set"' \
                  --before-context=50 | grep index | cut -d' ' -f6 )
echo "Alsa sink index is $alsa_sink_index"

# If the current default sink is not the USB, change it
current_sink_index=$(pacmd list-sinks | grep '*' | cut -d' ' -f5)
if [ $current_sink_index -ne $alsa_sink_index ]; then
   # Change the default to the alsa sink
   pacmd set-default-sink ${alsa_sink_index}
   echo "Default sink changed from $current_sink_index to $alsa_sink_index"
else
   echo "Default sink not changed - it is already $current_sink_index"
fi

# Set the USB speaker levels very low to start
amixer -c ${card_index} sset "Speaker" 5
echo "Speaker volume changed"

exit 0

Save the script (newspeaker.sh), and remember to make it executable with chmod +x newspeaker.sh. Test it a bit. When the speakers are plugged in and the script run manually, the audio from the USB speakers is excellent. After unplugging, sound reverts to the onboard speakers. This is not a headphone jack - the audio must be stopped/started to use the changed