Re: [LAU] ACPI, HW and Jack issues? "[solved]"

On Thu, 14 May 2009 12:02:34 +0200
"Jostein Chr. Andersen" <jostein@email-addr-hidden> wrote:

> I', really sorry about the noise, but think I did it right this time:
>
> On Wednesday 13 May 2009 23.06.05 hollunder@email-addr-hidden wrote:
> ...
> >
> > The question is if this is a calculated or real (measured) value.
> > Consider measuring with jdelay.
>
> I physically connected a patch cable between the 1010's channel 3 out
> an in and then in qjackctrl connected jack_delay's out to system
> playback_3 and system capture_3 to jack_delay's in. Now, the picture
> changed totally:

Yep, that's the way to do it.
I did it wrong at first as well..

> With latencies 2.9 according to qjackctl:
> capture latency = 64
> playback_latency = 128
> 262.197 frames 5.946 ms
> 262.190 frames 5.945 ms
> 262.190 frames 5.945 ms
> 262.190 frames 5.945 ms
> 262.191 frames 5.945 ms
>
> and with latency 0.726 according to qjackctl:
> capture latency = 16
> playback_latency = 32
> 117.187 frames 2.657 ms
> 117.190 frames 2.657 ms
> 117.191 frames 2.657 ms
> 117.191 frames 2.657 ms
> 117.191 frames 2.657 ms

These values look good to me, just remember that the nicest values
won't help you unless you can get them under heavy load without xruns.
Expect worse numbers from your usb device. I have some measurements
from mine and some other people were so kind to provide some as well,
just need to put them together for a comparison some day.

> But this just mean that latency because the soundcard is at the best
> 2.7 ms when sending sound from it's out to it's in and it is better
> when just recording, right?

Yes, this is round-trip latency, just in or just out will be faster
(take half(?) the time).

> And apps that is jack only connected
> still have 0.4 ms latency?

From which measurement do you conclude that?
Jack itself shouldn't really add latency afaik but I'm no expert.

> Thanks for pointing me to jack_delay.
>
> Jostein

You're welcome, it's a really handy tool (if you are interested in
real, not just low, numbers).

Regards,
Philipp
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Received on Thu, 14 May 2009 15:52:10 +0200