SND_UAUDIO(4FREEBSD) - Linux man page online | Special files

USB audio and MIDI device driver.

November 12, 2016
SND_UAUDIO(4) BSD Kernel Interfaces Manual SND_UAUDIO(4)


snd_uaudio — USB audio and MIDI device driver


To compile this driver into the kernel, place the following lines in your kernel configura‐ tion file: device sound device usb device snd_uaudio Alternatively, to load the driver as a module at boot time, place the following line in loader.conf(5): snd_uaudio_load="YES"


The snd_uaudio driver provides support for USB audio class devices and USB MIDI class devices. 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 con‐ trol). 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 receiv‐ ing 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 con‐ trols. Some mixer controls are only available as dev.pcm.%d.mixer sysctls.
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snd_uaudio(4freebsd) referred by pcm(4freebsd) | snd(4freebsd) | sound(4freebsd)
refer to sound(4freebsd) | usb(4freebsd)
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