[pulseaudio-discuss] Why does the USB headset show the Digital Output (S/PDIF) port?

[zhaochengyi at uniontech.com]

Hi guys,

I have a USB headset that the module is Edifier USB K800.
Plug it into the PC's usb port, and then I found "Digital Output 
(S/PDIF)" audio port as below.

Would you please tell me why the Digital Output (S/PDIF) port has been 
shown, and how to verify if this USB headset really have the output 
function of Digital Output (S/PDIF), and how to close this audio port.

Thanks a lot!

-------------------------------------------------------------------------

$ pacmd list-cards
     index: 3
         name: 
<alsa_card.usb-C-Media_Electronics_Inc._USB_PnP_Sound_Device-00>
         driver: <module-alsa-card.c>
         owner module: 27
         properties:
                 alsa.card = "2"
                 alsa.card_name = "USB PnP Sound Device"
                 alsa.long_card_name = "C-Media Electronics Inc. USB PnP 
Sound Device at usb-0000:03:00.3-2, full speed"
                 alsa.driver_name = "snd_usb_audio"
                 device.bus_path = "pci-0000:03:00.3-usb-0:2:1.0"
                 sysfs.path = 
"/devices/pci0000:00/0000:00:08.1/0000:03:00.3/usb1/1-2/1-2:1.0/sound/card2"
                 udev.id = 
"usb-C-Media_Electronics_Inc._USB_PnP_Sound_Device-00"
                 device.bus = "usb"
                 device.vendor.id = "0d8c"
                 device.vendor.name = "C-Media Electronics, Inc."
                 device.product.id = "013a"
                 device.product.name = "USB PnP Sound Device"
                 device.serial = 
"C-Media_Electronics_Inc._USB_PnP_Sound_Device"
                 device.string = "2"
                 device.description = "USB PnP Sound Device"
                 module-udev-detect.discovered = "1"
                 device.icon_name = "audio-card-usb"
         profiles:
                 input:analog-mono: Analog Mono Input (priority 7, 
available: unknown)
                 output:analog-stereo: Analog Stereo Output (priority 
6500, available: unknown)
                 output:analog-stereo+input:analog-mono: Analog Stereo 
Output + Analog Mono Input (priority 6507, available: unknown)
                 output:iec958-stereo: Digital Stereo (IEC958) Output 
(priority 5500, available: unknown)
                 output:iec958-stereo+input:analog-mono: Digital Stereo 
(IEC958) Output + Analog Mono Input (priority 5507, available: unknown)
                 output:iec958-ac3-surround-51: Digital Surround 5.1 
(IEC958/AC3) Output (priority 300, available: unknown)
                 output:iec958-ac3-surround-51+input:analog-mono: 
Digital Surround 5.1 (IEC958/AC3) Output + Analog Mono Input (priority 
307, available: unknown)
                 off: Off (priority 0, available: unknown)
         active profile: <output:iec958-stereo+input:analog-mono>
         sinks:
 
alsa_output.usb-C-Media_Electronics_Inc._USB_PnP_Sound_Device-00.iec958-stereo/#4: 
USB PnP Sound Device Digital Stereo (IEC958)
         sources:
 
alsa_output.usb-C-Media_Electronics_Inc._USB_PnP_Sound_Device-00.iec958-stereo.monitor/#6: 
Monitor of USB PnP Sound Device Digital Stereo (IEC958)
 
alsa_input.usb-C-Media_Electronics_Inc._USB_PnP_Sound_Device-00.analog-mono/#7: 
USB PnP Sound Device Analog Mono
         ports:
                 analog-input-mic: Microphone (priority 8700, latency 
offset 0 usec, available: unknown)
                         properties:
                                 device.icon_name = "audio-input-microphone"
                 analog-output-speaker: Speakers (priority 10000, 
latency offset 0 usec, available: unknown)
                         properties:
                                 device.icon_name = "audio-speakers"
                 iec958-stereo-output: Digital Output (S/PDIF) (priority 
0, latency offset 0 usec, available: unknown)
                         properties:

-------------------------------------------------------------------------
$ amixer -c 2 contents
numid=10,iface=CARD,name='Keep Interface'
   ; type=BOOLEAN,access=rw------,values=1
   : values=off
numid=3,iface=MIXER,name='Mic Playback Switch'
   ; type=BOOLEAN,access=rw------,values=1
   : values=off
numid=4,iface=MIXER,name='Mic Playback Volume'
   ; type=INTEGER,access=rw---R--,values=1,min=0,max=127,step=0
   : values=0
   | dBminmax-min=0.00dB,max=23.81dB
numid=7,iface=MIXER,name='Mic Capture Switch'
   ; type=BOOLEAN,access=rw------,values=1
   : values=on
numid=8,iface=MIXER,name='Mic Capture Volume'
   ; type=INTEGER,access=rw---R--,values=1,min=0,max=16,step=0
   : values=3
   | dBminmax-min=0.00dB,max=23.81dB
numid=9,iface=MIXER,name='Auto Gain Control'
   ; type=BOOLEAN,access=rw------,values=1
   : values=on
numid=5,iface=MIXER,name='Speaker Playback Switch'
   ; type=BOOLEAN,access=rw------,values=1
   : values=on
numid=6,iface=MIXER,name='Speaker Playback Volume'
   ; type=INTEGER,access=rw---R--,values=2,min=0,max=151,step=0
   : values=54,54
   | dBminmax-min=-28.37dB,max=-0.06dB
numid=2,iface=PCM,name='Capture Channel Map'
   ; type=INTEGER,access=r----R--,values=1,min=0,max=36,step=0
   : values=0
   | container
     | chmap-fixed=MONO

numid=1,iface=PCM,name='Playback Channel Map'
   ; type=INTEGER,access=r----R--,values=2,min=0,max=36,step=0
   : values=0,0
   | container
     | chmap-fixed=FL,FR

----------------------------------------------------------------

Best regards,
Chengyi