[linux-audio-user] terrible soundwith jackd/pro audio apps

Matt Price matt.price at utoronto.ca
Fri Feb 2 14:43:33 EST 2007


Hi folks,

all this is on a laptop running ubuntu feisty with latest updates and a
few packages from offsite (e.g. ardour2, traverso).

I want to use my laptop to edit and produce rough cuts of audio
documentaries.  This whole project takes place in the digital domain --
clips are recorded to high-bitrate mp3 and dumped to my hd over usb, and
the final product is always either an mp3 or a wav file.  I only use my
sound card to listen to the piece as I'm working on it, so I'd hoped
that the fact that it's a cheap intel_hda sound card wouldn't matter
that much.

Up to now I've been using audacity 1.3b, and it works  ok but I find the
interface somewhat clumsy and inflexible.  ardour2 and traverso both
have much more powerful interfaces, in my opinion.  Unfortunately
neither of these apps seems to work right for me.  In particular, both
of them produce very choppy and static-ridden audio, especially ardour2.
traverso is also somewhat unstable -- too bad, since it's very fast and
I love the interface.  

traverso works somewhat better with the alsa driver than it does with
the jack driver, so naturally my suspicions turn to jackd, with which I
have little experience.  Here's my setup:

-normally run with a lightly-modified ubuntu 2.6.19 kernel, which uses
the 'voluntary preemption' switch and hz_250; I've also installed and
been trying out the stock 'lowlatency' kernel which enables full
preemption and hz_1000.  fyi, here's what grep says about the configs:

matt at gont:~$ grep -i hz /boot/config-2.6.19-7-ref-generic 
# CONFIG_HZ_100 is not set
CONFIG_HZ_250=y
# CONFIG_HZ_1000 is not set
CONFIG_HZ=250
CONFIG_MACHZ_WDT=m
matt at gont:~$ grep -i hz /boot/config-2.6.20
config-2.6.20-5-generic     config-2.6.20-6-lowlatency
config-2.6.20-6-generic     
matt at gont:~$ grep -i hz /boot/config-2.6.20-6-lowlatency 
# CONFIG_HZ_100 is not set
# CONFIG_HZ_250 is not set
# CONFIG_HZ_300 is not set
CONFIG_HZ_1000=y
CONFIG_HZ=1000
CONFIG_MACHZ_WDT=m
CONFIG_NO_IDLE_HZ=y
matt at gont:~$ grep -i preem /boot/config-2.6.20-6-lowlatency 
# CONFIG_PREEMPT_NONE is not set
# CONFIG_PREEMPT_VOLUNTARY is not set
CONFIG_PREEMPT=y
CONFIG_PREEMPT_BKL=y
CONFIG_DEBUG_PREEMPT=y

I usually run jackd from the commandline thus:

/usr/bin/jackd -R  -dalsa -dhw:0 

this is with the realtime-lsm module installed and loaded, running as
gid 29, so the user has access to the lowlatency stuff.  I have
definitely noticed some improvements usintg the lowlatency kernel, but
it's all still not very good.  This really does surprise, me, so I'm
wondering what adjustments I might try to make to my setup to improve
jack's performance, and with it, the performance of either traverso or
ardour2.  I've been messing around with jack options, esp. the --period
option (made it as high as I could, 4096) and the -s option (without it
I get lots and lots and LOTS of xruns).  I think that both of these help
a little, but in the end I still have audio which is at the very least
clipped and unclear.  the same clips sound way way better in audacity
running aoss -- so my hardware is clearly capable of handling the audio
itself, evne while processing multiple other signals from e.g. amarok or
aplay.  but with jack it's a no-go, and unfortunately iwth traverso as
well.  nor do I think my cpu is the issue here -- I have a dell latitude
d820, with a core-duo running at 1.83gHz.  

I really don't need very low latency since I'm not working with music,
but with fairly rough vocal tracks and ambient sounds.  But I do want a
well-funcitoning editor/mixer.  

I hope this is the right place to ask for help!  thanks,

matt

-- 
Matt Price
History Dept
University of Toronto
matt.price at utoronto.ca
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