Bug#704305: more observations

[Daniel Pocock]

Here are some more observations about the problem and a hack that makes
it work.

The outright failure situation (e.g. the errors in the original bug
report) can often be resolved by unplugging the USB device and
reconnecting it and then restarting pulseaudio.

The system where the USB sound device was working well is a HP
Microserver, with no built in audio device.  If the Creative USB device
is connected to the Microserver, sound comes out on the analog ports by
default.  To force it to play sound via the optical port, I had to put
this in /etc/pulse/system.pa:

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

That is quite acceptable for a static server config.

Now, on to the laptop.  The typical use case for a laptop is plug and
play, so I am trying to avoid using any hacks like that in the config.
Nonetheless, I've found that I can make the sound come out of the
optical port with this entry in /etc/pulse/default.pa:

  load-module module-alsa-sink device=hw:1,2

This seems a little bit bizarre.  While the card number change from 0 to
1 is understandable when moving to different host, it is not clear why
the device number changes from 1 to 2.

Before trying these config hacks, I tried all the permutations of output
settings using the Gnome sound preferences panel and the pavucontrol
tool as well.  I had no luck with either of them (unless I give up on
using the optical output and just send sound to the analog port).  This
makes me feel that normal desktop/laptop users will struggle with this.

Here is the aplay output for the device connected to the laptop:


$ aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: PCH [HDA Intel PCH], device 0: CONEXANT Analog [CONEXANT Analog]
  Subdevices: 0/1
  Subdevice #0: subdevice #0
card 0: PCH [HDA Intel PCH], device 3: HDMI 0 [HDMI 0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: PCH [HDA Intel PCH], device 7: HDMI 1 [HDMI 1]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: PCH [HDA Intel PCH], device 8: HDMI 2 [HDMI 2]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: HD [USB Sound Blaster HD], device 0: USB Audio [USB Audio]
  Subdevices: 0/1
  Subdevice #0: subdevice #0
card 1: HD [USB Sound Blaster HD], device 1: USB Audio [USB Audio #1]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: HD [USB Sound Blaster HD], device 2: USB Audio [USB Audio #2]
  Subdevices: 0/1
  Subdevice #0: subdevice #0


$  aplay -L
null
    Discard all samples (playback) or generate zero samples (capture)
pulse
    PulseAudio Sound Server
default:CARD=PCH
    HDA Intel PCH, CONEXANT Analog
    Default Audio Device
sysdefault:CARD=PCH
    HDA Intel PCH, CONEXANT Analog
    Default Audio Device
front:CARD=PCH,DEV=0
    HDA Intel PCH, CONEXANT Analog
    Front speakers
surround40:CARD=PCH,DEV=0
    HDA Intel PCH, CONEXANT Analog
    4.0 Surround output to Front and Rear speakers
surround41:CARD=PCH,DEV=0
    HDA Intel PCH, CONEXANT Analog
    4.1 Surround output to Front, Rear and Subwoofer speakers
surround50:CARD=PCH,DEV=0
    HDA Intel PCH, CONEXANT Analog
    5.0 Surround output to Front, Center and Rear speakers
surround51:CARD=PCH,DEV=0
    HDA Intel PCH, CONEXANT Analog
    5.1 Surround output to Front, Center, Rear and Subwoofer speakers
surround71:CARD=PCH,DEV=0
    HDA Intel PCH, CONEXANT Analog
    7.1 Surround output to Front, Center, Side, Rear and Woofer speakers
hdmi:CARD=PCH,DEV=0
    HDA Intel PCH, HDMI 0
    HDMI Audio Output
hdmi:CARD=PCH,DEV=1
    HDA Intel PCH, HDMI 1
    HDMI Audio Output
hdmi:CARD=PCH,DEV=2
    HDA Intel PCH, HDMI 2
    HDMI Audio Output
default:CARD=HD
    USB Sound Blaster HD, USB Audio
    Default Audio Device
sysdefault:CARD=HD
    USB Sound Blaster HD, USB Audio
    Default Audio Device
front:CARD=HD,DEV=0
    USB Sound Blaster HD, USB Audio
    Front speakers
surround40:CARD=HD,DEV=0
    USB Sound Blaster HD, USB Audio
    4.0 Surround output to Front and Rear speakers
surround41:CARD=HD,DEV=0
    USB Sound Blaster HD, USB Audio
    4.1 Surround output to Front, Rear and Subwoofer speakers
surround50:CARD=HD,DEV=0
    USB Sound Blaster HD, USB Audio
    5.0 Surround output to Front, Center and Rear speakers
surround51:CARD=HD,DEV=0
    USB Sound Blaster HD, USB Audio
    5.1 Surround output to Front, Center, Rear and Subwoofer speakers
surround71:CARD=HD,DEV=0
    USB Sound Blaster HD, USB Audio
    7.1 Surround output to Front, Center, Side, Rear and Woofer speakers
iec958:CARD=HD,DEV=0
    USB Sound Blaster HD, USB Audio
    IEC958 (S/PDIF) Digital Audio Output