8 Aug
2008
8 Aug
'08
4:12 p.m.
Hi there!,
I want to optimize JACK capabilities in running Linux PCs.
What JACK configuration parameters do I have to vary (and in what way) to
achieve that?
(by "that" I mean: minimum latency, zero noise and zero xruns).
I'm looking for something like a "standard procedure"...
...not just trying all the possible configurations of JACK and picking up
the most convenient.
(... maybe an "autoJACKtuning" program can be done for this purpose, but
there MUST be a procedure to follow)
Maybe you just can't tune the best of every system by following the same
pattern, but making the average best is what i'm looking for.
I'm working in a program that's a metronome that reacts to human
synchronization errors (to the very same metronome).
That errors are just some milliseconds, and a further advance in the program
would need reacting as quickly as that - Fast!.
In some ways, the program is similar to a tap-tempo thing, but it's meant
for synchronization experiments.
That experiments are aimed at researching how do people sync themselves to
outer stimuli, like... the beat of a song.
Results of that can end up in cool stuff - e.g., the possibility of making
the sync of drum-machines REALLY human-like.
Well...
This program should be as "portable" as it can be.... but I'm having trouble
with some audio cards.
I don't think powerful sound cards are needed for this task... the
bottleneck seems much more of a OS scheduling thing.
I turned to JACK because of the promised low latencies and throughput (and
an easy API)...
... but sometimes the audio crackles, has xruns, can't get it to work even
with high latency, etc... and I don't have a clue about what to vary to fix
that.
Besides that, I'm kind of a musician too and it seems everybody who uses
JACK wants low low low latency and good sound, so a "guide" to tune up that
would be a step forward to the self promotion of JACK-based software.
Sorry for my Neanderthal-ish English
and cheers from Argentina,
Trece.
9 Aug
9 Aug
2:18 p.m.
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trece ocho wrote:
Hi there!,
I want to optimize JACK capabilities in running Linux
PCs.
Welcome Trece ;)
What JACK configuration parameters do I have to vary
(and in what way) to
achieve that?
(by "that" I mean: minimum latency, zero noise and zero xruns).
read `man jackd` - you want to set "-p <num> -n <num>"
-n: usually 2 or 3 - mostly depends on your sound-card
-p: 32,64,128,... 4096 "the period" defines buffer-size and latency
There's no "best" latency settings.
For recording you probably want to use a small period size for low
latency monitoring. But when you master, mix or edit: raise it up to
=1024 (many postprocessing effects are very CPU
intense, and you do not
need low latency to listen). Most versions of JACK allow
the period to
be changed during runtime: `man jack_bufsize`
Latency and Xruns are related: The higher the latency the less chance of
xruns. To get a 'zero-xrun' system you want to run jackd with
/realtime-priority/ on a realtime-patched linux kernel and lock the it's
pages into memory (no swap):
1. get or compile a realtime kernel
2. set up IRQs
3. permit audio users to use realtime capabilities
4. start jackd as user with realtime capabilities
For (1) I suggest to get a binary for your gnu/Linux distribution.
64studio, musix, ubuntu-studio, gentoo-pro-audio-overlay, CCRMA..
(2) 64studio offers a debian package rtirq for a great script from Rui:
http://www.linuxaudio.org/mailarchive/lau/2006/6/26/127914
There's probably other packages as well.
(3) that's the /etc/security/limits.conf part
http://tapas.affenbande.org/wordpress/?page_id=73
(4) /usr/bin/jackd -R -P 70 -T -d alsa -n 3 -r 48000 -p 128 -d hw:1,0
or use the "Realtime" checkbox in qjackctl's Setup dialog.
zero noise: N/A - check your cables ;)
I'm looking for something like a "standard
procedure"...
use qjackctl.
...but sometimes the audio crackles, has xruns,
can't get it to work
even with high latency, etc... and I don't have a clue about what to
vary to fix that.
aah, although this sound can be described as /noisy/, x-runs are no
*noise* ;) and are not only correlated to latency.
They're normal: Unix is //fair// to all users and sometimes does not
see a reason why it should keep playing your sound or even keep it in
memory UNLESS you tell it to do so. (steps 1-4 above)
There's a lot of background-jobs on a default gnu/Linux; fi. `updatedb`
may get in your way..
I'm working..
[..]
That sounds interesting. - I think you should post that to the
Linux-Audio-Users mailing list (or if you have questions about
program-code to linux-audio-dev). Here it is a little off-topic and you
may get more feedback there.
HTH,
robin
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11 Aug
11 Aug
12:53 p.m.
Thanks Robin, although you over-explained lots of stuff (and sometimes you
misunderstood me), the trick that made it work well in this particular PC
was:
/usr/bin/jackd -R -P 70 -T -d alsa -n 3 -r 48000 -p 128 -d
I always used qjackctl... I prefer the mouse to the keyboard, I'm just
trying to figure out what stuff in Qjackctl I configured different from that
console command.
(I already had done the rest of the stuff - the linux-rt kernel, etc, etc -
)
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linux-audio-tuning@lists.linuxaudio.org
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participants (2)
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Robin Gareus -
trece ocho