On 02/09/18 12:47, Ert Retre via freebsd-usb wrote:

attached are the config descriptors and the device dump of two uaudio
devices. Both exhibit distorted audio output. It sounds a little bit
like clipping / not feeding enough samples fast enough...

I played around with dev.pcm.2.bitperfect=1, dev.pcm.2.play.vchans=0,
dev.pcm.2.play.vchanrate and hw.snd.latency=1...10.

At some point vchanrate doesn't work anymore, it always stays at 4.0
audio, even when trying to go back to 2.0. I have to usbconfig reset the

Sometimes (rarely) when playing around I get clear audio output, but
when I try to reproduce it (going back to default value for the last
sysctl setting and then going back again to the same setting again), the
audio is distorted again.

To me it sounds like some kind of buffer is not big enough or the data
is not delivered fast enough to the uaudio device. But this is a
dual-socket system with:
      CPU: Intel(R) Xeon(R) CPU           E5620  @ 2.40GHz (2133.36-MHz
K8-class CPU)
      FreeBSD/SMP: Multiprocessor System Detected: 16 CPUs
      FreeBSD/SMP: 2 package(s) x 4 core(s) x 2 hardware threads
And while playing around with uaudio the system has a load of around 1,
so I would expect CPU/RAM is not an issue here.


What version of FreeBSD is this?

Try to enable hw.usb.uaudio.debug=16 during playback.


If your device is FULL speed, you cannot connect it via an external HUB for more than 2 channels, recording and playback simultaneously. There is a capacity issue (except when using XHCI) and it will cause clipping.

Can you send the full output from usbconfig?

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