[Jackit-devel] Re: [PD-announce] Re: [linux-audio-dev] ANN: k_jack v0.0.0.5 and Mammut v0.15

[Kai Vehmanen]

On Fri, 24 Jan 2003, Kjetil S. Matheussen wrote:

>> What does "cat /proc/asound/card0/pcm0[cp]/sub0/[hs]w_params" output
> I'm at work now, and we ~only have delta cards. At home I use a built-in
> sound-card on an nforce chipset. But I get nearly the same good
> performance in pd here as at home. So here is delta44 parameters:

Could you also send an output of pcm0[cp]/sub0/status...? 
Anyway, this is very good info.

> kjetism at hensten /proc/asound/card0/pcm0c/sub0 $ more hw_params
[...]
> period_size: 64
> buffer_size: 1728

So I guess this explains a lot. This equals to running jackd 
with "-p 64 -n 27" (and not as root or otherwise it will throw clients
out if they miss one 64 frame deadline). 

I'm quite sure you get much more reliable performance this way, although
JACK doesn't take advantage of multip-period buffer configurations very
well.  And this has its reasons. With a setup like shown above, you either
get a huge latency (64*1728/44100*1000=2500ms), or you get latency jitter
(latency varies between 1.45ms->2500ms). Both are something we'd _really_
want to avoid.

Because of the above reasons, JACK is designed for two or three
period operation (-n 2 or -n 3). This way we can achieve both low 
latency and avoid latency jitter. We could improve reliability by 
sacrificing one or both of these goals, but for many of the use scenarios 
we are aiming at, this is simply not acceptable.

--
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