USB mic on Linux

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USB-microphones are usually setup as /dev/dsp1 under Linux.

The stable version of Audacity will not find /dev/dsp1 unless there is also a device called /dev/dsp0. (This is a bug in PortAudio that should be fixed in a future version.)

To work around this bug, try setting the AUDIODEV environment variable (at a terminal):

    $ AUDIODEV=/dev/dsp1 audacity

or try running

    # ln -s /dev/dsp /dev/dsp0

as root. Please let us know whether this helps or not.

It is also possible to run Audacity through an ALSA emulation layer, with:

    $ aoss audacity

which should enable audacity to use ALSA-devices natively.

USB-microphone in ALSA

Detecting the device

Displaying a thorough list of USB-devices is done by issuing the command

    $ lsusb --verbose | less

Search for the lines which contains Audio and Control Device like in the screendump below:

    Bus 001 Device 004: ID 17a0:0001  
    Device Descriptor:
    bLength                18
    bDescriptorType         1
    bcdUSB               1.10
    bDeviceClass            0 (Defined at Interface level)
    bDeviceSubClass         0 
    bDeviceProtocol         0 
    bMaxPacketSize0         8
    idVendor           0x17a0 
    idProduct          0x0001 
    bcdDevice            0.01
    iManufacturer           1 Samson Technologies      
    iProduct                2 Samson C01U              
    iSerial                 0 
    bNumConfigurations      1
    Configuration Descriptor:
      bLength                 9
      bDescriptorType         2
      wTotalLength          177
      bNumInterfaces          2
      bConfigurationValue     1
      iConfiguration          0 
      bmAttributes         0x80
        (Bus Powered)
      MaxPower               90mA
      Interface Descriptor:
        bLength                 9
        bDescriptorType         4
        bInterfaceNumber        0
        bAlternateSetting       0
        bNumEndpoints           0
        bInterfaceClass         1 Audio
        bInterfaceSubClass      1 Control Device
        bInterfaceProtocol      0 
        iInterface              0 
        AudioControl Interface Descriptor:
          bLength                 9
          bDescriptorType        36
          bDescriptorSubtype      1 (HEADER)
          bcdADC               1.00
          wTotalLength           40
          bInCollection           1
          baInterfaceNr( 0)       1
          AudioControl Interface Descriptor:
          bLength                12
          bDescriptorType        36
          bDescriptorSubtype      2 (INPUT_TERMINAL)
          bTerminalID             1
          wTerminalType      0x0201 Microphone
          bAssocTerminal          2
          bNrChannels             2
          wChannelConfig     0x0003
            Left Front (L)
            Right Front (R)
         iChannelNames           0 
         iTerminal               0 

In the top row, (Bus 001 Device 004: ID 17a0:0001) is the USB bus number. In the listing there are many noteworthy preferences for the microphone, samplerates and the like.

To look for installed modules regarding the soundsystem, do a:

   $ lsmod | grep snd
   snd_intel8x0           33692  3
   snd_ac97_codec         92704  1 snd_intel8x0
   snd_ac97_bus            2304  1 snd_ac97_codec
   snd_usb_audio          78784  0
   snd_pcm_oss            53664  0
   snd_mixer_oss          18688  1 snd_pcm_oss
   snd_usb_lib            16640  1 snd_usb_audio
   snd_rawmidi            25504  1 snd_usb_lib
   snd_seq_device          8716  1 snd_rawmidi
   snd_hwdep               9376  1 snd_usb_audio
   snd_pcm                89864  5 snd_intel8x0,snd_ac97_codec,snd_usb_audio,snd_pcm_oss
   snd_timer              25220  2 snd_pcm
   snd                    55268  14 snd_intel8x0,snd_ac97_codec,snd_usb_audio,snd_pcm_oss,snd_mixer_oss,snd_rawmidi,snd_seq_device,snd_hwdep,snd_pcm,snd_timer
   soundcore              10208  1 snd
   snd_page_alloc         10632  2 snd_intel8x0,snd_pcm
   usbcore               130692  5 snd_usb_audio,snd_usb_lib,ehci_hcd,uhci_hcd

and look for the modules usbcore, snd_usb_audio, snd_usb_lib. If they are loaded, the USB sound should work.

To really make sure that ALSA has detected your USB microphone, do a:

    $ cat /dev/sndstat
    Audio Devices:
    0: Intel 82801DB-ICH4 (DUPLEX)
    1: Samson C01U
    0: Analog Devices AD1981B
    1: Samson C01U

To see if the USB-microphone is detected and installed, try:

    $ cat /proc/asound/pcm
    00-00: Intel ICH : Intel 82801DB-ICH4 : playback 1 : capture 1
    00-01: Intel ICH - MIC ADC : Intel 82801DB-ICH4 - MIC ADC : capture 1
    00-02: Intel ICH - MIC2 ADC : Intel 82801DB-ICH4 - MIC2 ADC : capture 1
    00-03: Intel ICH - ADC2 : Intel 82801DB-ICH4 - ADC2 : capture 1
    00-04: Intel ICH - IEC958 : Intel 82801DB-ICH4 - IEC958 : playback 1
    01-00: Samson C01U : capture 1


    $ arecord --list-devices
    card 0: I82801DBICH4 [Intel 82801DB-ICH4], device 0: Intel ICH [Intel 82801DB-ICH4]
      Subdevices: 1/1
      Subdevice #0: subdevice #0
    card 0: I82801DBICH4 [Intel 82801DB-ICH4], device 1: Intel ICH - MIC ADC [Intel 82801DB-ICH4 - MIC ADC]
      Subdevices: 1/1
      Subdevice #0: subdevice #0
    card 0: I82801DBICH4 [Intel 82801DB-ICH4], device 2: Intel ICH - MIC2 ADC [Intel 82801DB-ICH4 - MIC2 ADC]
      Subdevices: 1/1
      Subdevice #0: subdevice #0
    card 0: I82801DBICH4 [Intel 82801DB-ICH4], device 3: Intel ICH - ADC2 [Intel 82801DB-ICH4 - ADC2]
      Subdevices: 1/1
      Subdevice #0: subdevice #0
    card 1: default [Samson C01U              ], device 0: USB Audio [USB Audio]
      Subdevices: 1/1
      Subdevice #0: subdevice #0

There is also a couple of new devices in /dev/snd/, depending on the system and devices installed. An example may include:

  • PCM interface: /dev/snd/pcmC1D0c (Pulse Code Modulation - Card #1 Device #0 - capture)
  • Control interface : /dev/snd/controlC1 (Control Card #1)

To get a detailed list of all PCM's and their configuration, try:

     $ arecord --list-pcms

which will output all sound hardware on the system and its configuration. To most of us, its a heap of junk with no dicernible information, but it is good to know about how to get it on screen.

Setting the stage

To set the volume levels and other controls for your USB-mic, and get a nice Ncurses interface to do it in, do:

     $ alsamixer -c 1 # if your mic has card number 1 in the "arecord --list-devices" listing.

Be sure to unmute the capture channel, else no sound will be recorded anywhere.

Another mixer that can be used is aumix which is a more elaborate tool than the native Gnome mixer.

For the hardcore people out there, there is always the amixer, which is a text-based tool to set recording levels, muting and unmuting channels and so on. Some help may be found here.

Recording with ALSA

To test the recording capabilities of your USB-mic in Linux, there is a number of neat programs to try. However, since not all programs are especially designed for PlugNPlay with USB-mics, the ALSA development people has included a rather sluggish but usable recording utility that works without any fancy GUI and effect junk that could mess things up. It is called arecord and we have used its versatility above, to display devices and PCMs. It can also be used to record, hence the name.

The syntax for recording is:

    arecord -f [format] -D hw:card,device -d [duration]

and if one wishes to record in cd-quality for 20 seconds using the USB microphone detected as Card #1 Device #0 as in the listing above, and save it to test.wav issue the command:

    $ arecord -f cd -D hw:1,0 -d 20 test.wav

The result can be played using the aplay utility, also available in ALSA.

    $ aplay -f cd test.wav

If it works, then you will be able to use the microphone in any setting, even if you have to dabble a lot to get things working correctly.

Samson C01U USB-microphone

There are apparently some issues with using the Samson C01U USB-microphone under Linux. There are some documents outlining the problem:

  • First post (although with not entirely correct assumptions under the "Bad news" heading)
  • Follow-up


See also ...

... this Forum thread for further discussion.