[LAU] USB audio interface and a buggy USB controller

[Philipp Überbacher]

Excerpts from david's message of 2010-09-17 10:32:05 +0200:
> Philipp Überbacher wrote:
> > Excerpts from david's message of 2010-09-15 19:32:44 +0200:
> >> Monty Montgomery wrote:
> >>> Oh, I should say I've also just recently seen similar problems (for no
> >>> apparent reason) when an XHCI (3.0) controller hands off a full-speed
> >>> (1.1) isochronous device.  Is the port this is being plugged into a
> >>> USB 3.0 port ('SuperSpeed')?
> >> Someone said something earlier about hubs. I have a USB2 hub plugged 
> >> into a USB2 port on my laptop. When I tried using a Behringer UCA-202 
> >> (USB1.1) device through the hub, it could barely play, and not record at 
> >> all. Connected directly to a USB2 port, it plays and records fine.
> >>
> >> So original poster just might be dealing with an internal hub.
> > 
> > That usb hub stuff seems to be really strange. I do have an external
> > hub, but I only use it for HDs.
> > The USB interface is connected directly to one of the laptops ports.
> > 
> > The laptop seems to have an internal hub, or two?
> > Anyway, it works just fine, as far as I can tell. Some jack2 test I ran
> > showed quite immense jitter, but I guess that's normal with USB devices.
> > 
> > $ lsusb
> > Bus 007 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
> > Bus 006 Device 002: ID 0582:0074 Roland Corp. EDIROL UA-25
> > Bus 006 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
> > Bus 005 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
> > Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
> > Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
> > Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
> > Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
> 
> jack2 on my non-RT kernel laptop has no jitter at all working with 
> UCA-202 connected to a USB2 port on the laptop.
> 
> Lower signal levels and noise when connected via my self-powered 9-port 
> USB2 hub. Cheap hub, probably very bad ground or poor shielding.

It's not audible for me, but jack2 contains some tests, one of which
shows jitter as a graph. There's a paper by Stephane Letz that explains
all this stuff, but I don't have a link ready.
-- 
Philipp

--
"Wir stehen selbst enttäuscht und sehn betroffen / Den Vorhang zu
und alle Fragen offen." Bertolt Brecht, Der gute Mensch von Sezuan