[LAU] usb and jack

[Ray Rashif]

2009/10/25 <hollunder at gmx.at>

> On Sun, 25 Oct 2009 11:40:16 +0100
> rosea grammostola <rosea.grammostola at gmail.com> wrote:
>
> > Hi,
> >
> > I found this info:
> >
> >
> >       "USB and jack
> >
> > The USB interrupt period is 1 msec. To be able to get lower latency
> > with jack when using it with an USB device, you have to use a setting
> > as 48kHz and 3 period. It will makes the buffer time a multiple of 1
> > msec and you will get a much lower latency as with the default 2
> > period. Additionaly, loading the snd-usb-audio with the parameter
> > "nrpacks=1" will give you a much lower latency (for this to work take
> > care that CONFIG_USB_BANDWIDTH is not set and
> > CONFIG_USB_DYNAMIC_MINORS is not set in your running kernel)."
> >
> >
> >
> http://proaudio.tuxfamily.org/wiki/index.php?title=Howto_RT_Kernel#USB_and_jack
> >
> >
> > 1) is this info still up-to-date?
> > 2) how do I exactly take care of this:
> > "Additionaly, loading the snd-usb-audio with the parameter
> > "nrpacks=1" will give you a much lower latency (for this to work take
> > care that CONFIG_USB_BANDWIDTH is not set and
> > CONFIG_USB_DYNAMIC_MINORS is not set in your running kernel)"
> >
> > (Debian (based) systems)
> >
> > \r
>
> In my experience 48kHz/3 periods works a bit more stable, the possible
> latency settings in jack don't really change, 64 frames is still the
> lower boundary and unstable.
>
> But I haven't heard about  2)  and am very curious about this myself.
>
> Philipp


2) Edit /etc/modprobe.conf or /etc/modprobe.d/modprobe.conf with:

options snd-usb-audio nrpacks=1

And to "make sure". you have to have the kernel options changed. make
menuconfig, and press "/" to search for the two options.

Philipp: we already dealt with that one but _without_ substantial
cause-and-effect http://bugs.archaudio.org/task/5
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