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diff --git a/share/man/man4/snd_uaudio.4 b/share/man/man4/snd_uaudio.4
--- a/share/man/man4/snd_uaudio.4
+++ b/share/man/man4/snd_uaudio.4
@@ -57,12 +57,76 @@
USB digital input), output terminals (e.g.\& speakers), and a number of units
in between (e.g.\& volume control).
.Pp
+If there are no user-supplied values through the
+.Xr sysctl 8
+interface, the driver will select the best matching configuration supported by
+the device during attach, that is, the configuration with the highest sample
+rate and most channels and bits, if the device supports multiple configurations
+in the first place.
+.Pp
Refer to the
.Ql USB Audio Class Specification
for more information.
+.Sh SYSCTL VARIABLES
+The following variables are available as both
+.Xr sysctl 8
+variables and
+.Xr loader 8
+tunables.
+For a change to take effect during runtime, the device has to be re-attached.
+.Pp
+All user-supplied values have to be supported by the device, otherwise they are
+ignored.
+.Bl -tag -width indent
+.It Va hw.usb.uaudio.buffer_ms
+Period of audio data processed at once, in milliseconds, from 1 to 8 (default
+is 4). Lower values mean less latency, but this can result in audible gaps due
+to frequent CPU wakeups.
+Some devices might need higher values to work proprely.
+.It Va hw.usb.uaudio.default_bits
+Default sample size in bits, from 0 to 32 (default is 0).
+A value of 0 sets the sample bits to the maximum supported value.
+.It Va hw.usb.uaudio.default_channels
+Default number of sample channels, from 0 to 64 (default is 0).
+USB 1.1 devices are limited to 4 channels due to bandwidth constraints,
+although higher values can be set.
+A value of 0 sets the sample channels to the maximum supported value.
+.It Va hw.usb.uaudio.default_rate
+Default sample rate in Hz.
+If set to 0, the device's defaults will be used.
+Note that if VCHANs are enabled, the sample rate will be overriden by
+.Pa dev.pcm.%d.[play|rec].vchanrate
+(see
+.Xr sound 4 ) ,
+which can also be used to adjust the sample rate during runtime.
+.It Va hw.usb.uaudio.handle_hid
+Let
+.Nm
+handle HID volume keys, if any (default is 1).
+.Bl -tag -width 2n
+.It 0
+Disabled.
+.It 1
+Enabled.
+.El
+.El
+.Pp
+If
+.Xr usb 4
+has been compiled with
+.Va USB_DEBUG
+on, the following
+.Xr sysctl 8
+variable is also available:
+.Bl -tag -width indent
+.It Va hw.usb.uaudio.debug
+Debug output level (default is 0).
+.El
.Sh SEE ALSO
.Xr sound 4 ,
-.Xr usb 4
+.Xr usb 4 ,
+.Xr loader 8 ,
+.Xr sysctl 8
.Rs
.%T "USB Audio Class Specifications"
.%U http://www.usb.org/developers/docs/devclass_docs/

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