ReRe: [linux-audio-user] Demudi looking good, soundcard advice? (tweaking jack?)

tim hall tech at glastonburymusic.org.uk
Sat Oct 16 11:55:29 EDT 2004


Last Friday 15 October 2004 21:08, MarC was like:
> Emiliano Grilli wrote:
> >venerdì, 15 ottobre 2004 alle 00:01:21, MarC ha scritto:
[snip]
> >>Now I'm ""working"" with a Creative Audigy card and I want to buy a new
> >>one basically because Audigy doesn't allow realtime monitoring through
> >>jack (the latency is at least 45ms and for me is too much) and because
> >>I want to have a good dynamic response to record my acoustic guitar
> >>(now it saturates the input or I must record at a low volume with a lot
> >>of noise).
> >
> >Very strange that you cannot achieve better performance... I don't know
> > the audigy, but with a crappy sb128 on athlon 800 w 256Mb ram I can get
> > with "reasonably few" xruns to 23 ms and even to 11 (i speak of the
> > values reported by qjackctl) - I suspect that your problem comes from not
> > having an external mixer for conveniently routing of inputs and outputs
> > and for monitoring what you are playing.
> >
> >Could also be a problem of a not enough powerful pc?
>
> it's not a problem of the pc: 2.6Ghz, 512Mb ram
> it's a problem of *me* configuring it... :(
> as Free knows, I already suspected that I had some problems with my jack
> configuration so this comments are the definite proof of it.
>
> Indeed, I *could* configure qjackctl with a latency of 23ms(periods: 2,
> frames: 512 ): but I when I used Ardour I got some problems like the
> sound getting cut sometimes, it hanged often, strange inicialization
> errors, etc.

You may want to use a different configuration for different situations. For 
multitrack recording, obviously go as low as poss without xruns (256 
Frames/Period - x2 works for me on a Celeron 600 + 256M). For dsp and mixing 
it's worth allowing a longer period (1024 works for me).

> Also I though that I shouldn't allow any "xrun" and I disabled "Soft
> Mode". Now I see I "must" allow "xruns" but what criteria do I follow?
> how much "xruns" can be allowed?

It's not really how much xruns, it's more where they occur. Right in the 
middle of an important take is bad. If they only happen when you're messing 
about onscreen then you just have to discipline yourself to keep your hands 
off the mouse. Really you don't want any [ha!], but having Jack exit every 
single time you hit an xrun can be equally annoying.

> And finally, to tweak jack configuration, I ignore if it can be useful
> to change other parameters.
> Now I only play with "periods" and "frames", and I don't know the exact
> influence of the parameters: "Start Delay"(why jack has an initial
> delay?) and "Timeout"(of what? it sounds the same than latency...). I
> didn't found docs about jack about these issues... Does anybody know?
> Should I try the jackit user list or it is too technical?

I have a start delay of 2 secs and a timeout of 500ms. The former gives Jack 
longer to start up - I assume it allows the prefilling of buffers or somesuch 
[?]. The latter means it waits longer before giving up. AFIU

> If there isn't documents on these questions, when I'll finish, I'll try
> to write it down and make a "beginner's" doc.
> Also I think that it should be a place where the people could post their
> experiences in different sound cards in linux and their jack
> configurations under different environments. This should make our life
> easier...

I assume you're familiar with:
http://www.agnula.org/download/demudi/1.2.0-FAQ
http://wiki.agnula.org/ is a good place to start work on additional 
information that is needed. It would be brilliant if more people used it ;)

cheers

tim hall



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