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Alternatively, to load the driver as a module at boot time, place the following line in loader.conf(5):
snd_uaudio_load="YES"
A USB audio device consists of a number of components: input terminals (e.g.amp; USB digital input), output terminals (e.g.amp; speakers), and a number of units in between (e.g.amp; volume control).
If the device supports multiple configurations, and there have been no user-supplied values specified through the sysctl(8) interface, the driver will select the best matching configuration supported by the device during attach. "Best" means the configuration with the most channels and highest quality in sample rate and sample size.
Refer to the ‘USB Audio Class Specification’ for more information.
| 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. | |
| hw.usb.uaudio.default_bits | |
|
Preferred sample size in bits, from 0 to 32 (default is 0).
A value of 0 sets the sample size to the maximum supported sample size.
Set this to select a smaller sample size if the device supports multiple sample sizes. | |
| hw.usb.uaudio.default_channels | |
|
Preferred number of sample channels, from 0 to 64 (default is 0).
USB 1.1 devices are limited to 4 channels due to bandwidth constraints, unless
a higher value is explicitly requested.
A value of 0 sets the sample channels to the maximum supported channel number.
Set this to select a smaller channel number if the device supports multiple channel configurations. | |
| hw.usb.uaudio.default_rate | |
|
Preferred sample rate in Hz (default is 0).
If set to 0, the device's highest supported sample rate will be used.
Note that if VCHANs are enabled, the sample rate will be overridden by dev.pcm.%d.[play|rec].vchanrate (see sound(4)), which can also be used to adjust the sample rate during runtime. If hw.usb.uaudio.default_rate is non-zero, dev.pcm.%d.[play|rec].vchanrate will use it as its maximum allowed value. | |
| hw.usb.uaudio.handle_hid | |
| Let snd_uaudio handle HID volume keys, if any (default is 1). | |
| 0 | Disabled. |
| 1 | Enabled. |
If usb(4) has been compiled with USB_DEBUG on, the following setting is also available:
| hw.usb.uaudio.debug | |
| Debug output level (default is 0). | |
USB Audio Class Specifications,
| SND_UAUDIO (4) | February 15, 2025 |
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