[LAU] Sound Devices USBPre2, UAC2 status

[shal at free.fr]

----- Mail original -----
> De: "Hans Wilmers" <hanswil at notam02.no>
> À: linux-audio-user at lists.linuxaudio.org
> Envoyé: Jeudi 10 Janvier 2013 13:23:57
> Objet: Re: [LAU] Sound Devices USBPre2, UAC2 status
> 
> On 01/07/2013 08:25 PM, shal at free.fr wrote:
> >
> > ----- Mail original -----
> >> De: "alexander" <axeldenstore at gmail.com>
> >> À: linux-audio-user at lists.linuxaudio.org
> >> Envoyé: Lundi 7 Janvier 2013 18:27:42
> >> Objet: Re: [LAU] Sound Devices USBPre2, UAC2 status
> >> I also own this interface, recently it has started to work in uac2
> >> mode,
> >> I still cant raise the samplerate, but it runs.. however, It still
> >> runs
> >> alot better in uac1.. when in uac2 jack mysteriously shuts down
> >> for
> >> no
> >> appearant reason. I run archlinux, allways uptodated with vanilla
> >> kernel.
> >>
> >> This is when I connect it without pressing 1. eg, uac2
> >> http://pastebin.com/BFJTwXnJ
> >> And as with pressing 1. http://pastebin.com/ZJ1jbPUK
> >
> >
> > Hi,
> >
> > In my understanding, you are not in UAC2 , you are in high-speed
> > mode but the usb audio protocol remains UAC1.
> >
> >
> > In the kernel source in the file include/uapi/linux/usb/audio.h is
> > defined two values:
> > /* bInterfaceProtocol values to denote the version of the standard
> > used */
> > #define UAC_VERSION_1			0x00
> > #define UAC_VERSION_2			0x20
> >
> > So if the card is in UAC2 , you should see bInterfaceProtocol at 32
> > (or 0x20)
> > By example, now the RME babyface is recognize as UAC2 device, you
> > can view its "lsub -v" here  : http://minilien.fr/a0m3kc
> >
> > But for the usbPre2 device with ou without pressing the "1" button,
> >  we have bInterfaceProtocol = 0. So we stays in UAC1, even the
> > speed increase to high-speed.
> >
> 
> I was also surprised to see that the USBPre2 now works duplex without
> pressing the "1" button while connecting.
> 
> This was tested on Fedora 17 with stock kernel 3.6.6-1.fc17.
> Jack was set to 512 Frames/period and 3 periods/buffer, and in a 24h
> recording I got no xruns.
> I did not manage to choose a sample rate unlike 48000, though.
> 
> With lsusb, I can see 2 configurations for the same device, and the
> second one has bInterfaceProtocol = 32 for all interfaces except HID:
> http://pastebin.com/zwq0VVbM


Hi Hans,

Thank you for provided information.

So, some usbPre2 have bNumConfigurations=2 when "1" is not pressed but not all usbPre2 (mine or alexander devices have only one "Configuration Descriptor").  Your device descriptor contains a UAC2 configuration descriptor, This sound good.

Perhaps there is different firmware ?
I have the 1.03 firmware. Can you provide your firmware level ?
Can you test 192khz value in jackd ?

Olivier