[LAU] lowest usable latency from a USB 1 device?

[Rui Nuno Capela]

On 09/16/2011 06:33 PM, Paul Davis wrote:
> if you can run a USB 1 class compliant audio device on your linux
> system with lower latency than the current minimum so far posted to
> this thread, please post with the settings you use and the type of
> device. if your best performance has already been posted, no need to
> repeat it.
>
> i'll get the ball rolling with 2048 frames. note that we are assuming
> 2 channels only, but duplex mode (simultaneous capture+playback).
>

with my, now old but "semper fi", tascam us-224 i've been happy with 
-r48000 -p128 -n2, for ages (5y+). thanks to Karsten Wiese and me self 
on this old and rusty us-x2y alsa "rawusb" jackd backend ;) alas, it is 
not the world class compliant snd-usb-audio you're asking about but a 
formerly derived one, snd-usb-usx2y.

but then, years have turned, and some usb 1.1 crappy devices (read very 
cheap, like the ones fitting like a usb mini-dongle, with only one 
line-out and other in) it's been quite usable with -r48000 -p128 -n3. 
this time using that classy snd-usb-audio ;)

aha, it helps a lot having a full preempt_rt (or threadirqs enabled) 
kernel and then fine tuned irq service threads priorities (think of, 
yours truly rtirq:)

cheers
-- 
rncbc aka Rui Nuno Capela
rncbc at rncbc.org