mea wrote:
Hello from Prague,
I bought the firewire soundcard Edirol FA-66. Yesterday morning I
compiled freebob, recompiled jack and within half an hour I already saw
all 6 inputs and outputs in qjackctl. What? Recording on linux is hard?
Pha! I thought but unfortunately my moment of victory didn't last long.
On all recordings there is a strange cracking sound, not all the time,
but every couple of seconds. No xruns though. Before I bought this
device I used to record through the internal soundcard of my thinkpad
R40, running all programs as root and this 'sort of' worked. So I
thought I should first of all make sure all my apps can run as user.
After a lot of reading (I spent all day on this yesterday before I
decided to consult this list) I figured the best approach for me would
be to use set_rlimits, because slackware doesn't have PAM, and I never
patched a kernel before. As I understand these are the 3 possibilities
for programs to run in realtime right? Well, in short I can now run
qjackctl, jack and ardour as user without xruns, but this weird cracking
is still on the recordings. To make sure it was not an ardour issue I
tried sooperlooper, and the noise is still there. I suspect the trouble
is probably freebob, because I didn't have this issue before and maybe I
should have written on their list, but I am not completely sure and I
found very useful information here before, so here I am, asking for any
advice, because I don't know what to do anymore. Here is some more
information about my setup>
The crackles you hear are due to libfreebob not being able to process
the firewire packets fast enough. This means lost packets and hence lost
audio data. You would expect xruns when this happens, but freebob-1.0
doesn't report dropped packets as xruns, this could be called a bug.
We'll fix this in the next version.
In order to use FreeBoB, it is really recommended to use a realtime
patched kernel. We are doing in userspace what is normally done in
kernel space, and hence we need to meet very strict deadlines to be able
to. When using a realtime patched kernel that is configured correctly
(see
http://freebob.sourceforge.net/index.php/System_Configuration_Hints), no
packets are dropped and this problem does not occur.
Having said this, you can probably improve things on a standard kernel
if you allow user processes to request SCHED_FIFO scheduling (realtime
scheduling). As a test you can run jackd+freebob as root and see if the
problem persists. Remember to start jackd in realtime mode:
e.g.
jackd -R -p60 -d freebob -p512
Thinkpad R40, Pentium4, 512MbRAM
You should check the brand of the firewire controller that you are
using. (some) Thinkpads have a Ricoh firewire controller built in, and
that is a very buggy piece of hardware. It will never work properly with
freebob because it fails on isochronous traffic. (check this using lspci -v)
The solution for that is to use a cardbus firewire controller. Chipsets
from Via, Texas Instruments and Nec are working fine for me.
Slackware 10.2
uname -r 2.6.13
Should it be possible, maybe consider switching to a more audio friendly
distro...
Greets,
Pieter Palmers
FreeBoB developer
