usb and jack

[rosea]

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


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[hollunder]

On Sun, 25 Oct 2009 11:40:16 +0100
rosea grammostola <rosea.grammostola@...> 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
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[Ray Rashif]

2009/10/25 <hollunder@...>

On Sun, 25 Oct 2009 11:40:16 +0100
rosea grammostola <rosea.grammostola@...> 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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[hollunder]

On Sun, 25 Oct 2009 18:03:09 +0800
Ray Rashif <schivmeister@...> wrote:

> 2009/10/25 <hollunder@...>
>
> > On Sun, 25 Oct 2009 11:40:16 +0100
> > rosea grammostola <rosea.grammostola@...> 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

Thanks, you're right, CONFIG_USB_DYNAMIC_MINORS is not set and CONFIG_USB_BANDWIDTH doesn't
even show up.

I'll try to load with that option tomorrow and see how it goes.

Philipp
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[Martin Homuth-Rosemann]

hollunder@... schrieb:

> On Sun, 25 Oct 2009 18:03:09 +0800
> Ray Rashif <schivmeister@...> wrote:
>
>  
>> 2009/10/25 <hollunder@...>
>>
>>    
>>> On Sun, 25 Oct 2009 11:40:16 +0100
>>> rosea grammostola <rosea.grammostola@...> 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
>>    
>
> Thanks, you're right, CONFIG_USB_DYNAMIC_MINORS is not set and CONFIG_USB_BANDWIDTH doesn't
> even show up.
>
> I'll try to load with that option tomorrow and see how it goes.
>
> Philipp
> _______________________________________________
> Linux-audio-user mailing list
> Linux-audio-user@...
> http://lists.linuxaudio.org/mailman/listinfo/linux-audio-user
>  

Hi,

don't know where I found this on the net that setting the buffer size
for usb audio a multiple of 1 ms duration, e.g. for 48000 kHz p=48 will
allow very low latencies. I tried this today with the latest rt kernel
and the cheap burr brown usb codec pcm2902 used in my behringer uca202:

options snd_usb_audio nrpacks=1

/usr/bin/jackd -R -P79 -dalsa -dhw:1,0 -r48000 -p48 -n2 -Xseq


It runs smoothly on a centrino laptop (pentium M, cpu freq stepping
between 0.6 and 1.6 GHz).
I built a plain vanilla 2.6.31.12 with the latest rt20 patch applied,
debs available my repo - read more:
http://www.sidux.com/index.php?name=PNphpBB2&file=viewtopic&t=9396&start=87
Imho the latest rt20 is much more robust than rt19 - I like it!

Maybe some of the jack and usb gurus (Paul?, Clemens?) can confirm the
-p48 -n2 setting.

Ciao Martin
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[Paul Davis]

On Sun, Jan 24, 2010 at 6:52 AM, Martin Homuth-Rosemann
<linuxaudio@...> wrote:
> Maybe some of the jack and usb gurus (Paul?, Clemens?) can confirm the
> -p48 -n2 setting.

clemens is the guru; i'm the USB hater ...

friends don't let friends do audio over USB, etc.
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[Clemens Ladisch]

Martin Homuth-Rosemann wrote:
> don't know where I found this on the net that setting the buffer size
> for usb audio a multiple of 1 ms duration, e.g. for 48000 kHz p=48 will
> allow very low latencies. I tried this today with the latest rt kernel
> and the cheap burr brown usb codec pcm2902 used in my behringer uca202:
>
> options snd_usb_audio nrpacks=1

You don't need this option; the driver was fixed to use sensible
values years ago.

> /usr/bin/jackd -R -P79 -dalsa -dhw:1,0 -r48000 -p48 -n2 -Xseq
>
> It runs smoothly on a centrino laptop (pentium M, cpu freq stepping
> between 0.6 and 1.6 GHz).
>
> Maybe some of the jack and usb gurus (Paul?, Clemens?) can confirm the
> -p48 -n2 setting.

For most USB audio devices, using period sizes that are an integer
multiple to the USB packet size (1 ms) will definitely help.  Some
devices like the SB Audigy 2 NX or UA-101 do not synchronize their
sample clock to the USB clock (and this has nothing to do with USB
2.0), and in those cases, the period size does not matter.

(I did not know that Jack now supports lengths that are not powers
of two.)


Best regards,
Clemens
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