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     snd_uaudio — USB audio and MIDI device driver


     To compile this driver into the kernel, place the following lines in your kernel
     configuration file:

           device sound
           device usb
           device snd_uaudio

     Alternatively, to load the driver as a module at boot time, place the following line in



     The snd_uaudio driver provides support for USB audio class devices and USB MIDI class

     A USB audio device consists of a number of components: input terminals (e.g. USB digital
     input), output terminals (e.g. speakers), and a number of units in between (e.g. volume

     Refer to the ‘USB Audio Class Specification’ for more information.


     sound(4), usb(4)

     USB Audio Class Specifications,


     The snd_uaudio driver first appeared in FreeBSD 4.7.


     This manual page was adopted from NetBSD 1.6 and modified for FreeBSD by Hiten Pandya


     The PCM framework in FreeBSD only supports synchronous device detach.  That means all mixer
     and DSP character devices belonging to a given USB audio device must be closed when
     receiving an error on a DSP read, a DSP write or a DSP IOCTL request.  Else the USB audio
     driver will wait for this to happen, preventing enumeration of new devices on the parenting
     USB controller.

     Some USB audio devices might refuse to work properly unless the sample rate is configured
     the same for both recording and playback, even if only simplex is used.  See the
     dev.pcm.%d.[play|rec].vchanrate sysctls.

     The PCM framework in FreeBSD currently doesn't support the full set of USB audio mixer
     controls.  Some mixer controls are only available as dev.pcm.%d.mixer sysctls.