View source for USB mic on Linux

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 <tt>Audio</tt> and <tt>Control Device</tt> 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 <tt>usbcore, snd_usb_audio, snd_usb_lib</tt>. 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
     .
     .
     Mixers:
     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

or
     $ 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 <tt>/dev/snd/</tt>, depending on the system and devices installed. An example may include:

* PCM interface: <tt>/dev/snd/pcmC1D0c</tt> (Pulse Code Modulation - Card #1 Device #0 - capture)
* Control interface : <tt>/dev/snd/controlC1</tt> (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 <tt>aumix</tt> which is a more elaborate tool than the native Gnome mixer.

For the hardcore people out there, there is always the <tt>amixer</tt>, which is a text-based tool to set recording levels, muting and unmuting channels and so on. Some help may be found [http://dsl.org/cookbook/cookbook_27.html 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 <b><tt>arecord</tt></b> 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 <tt>test.wav</tt> issue the command:

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

The result can be played using the <tt>aplay</tt> 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:

* [http://www.w140.com/audio/c01u_usb_old.html First post] (although with not entirely correct assumptions under the "Bad news" heading)
* [http://www.w140.com/audio/c01u_usb.html Follow-up]




-

== See also ... ==

... [http://audacityteam.org/forum/thread/312;nocount this Forum thread] for further discussion.