[ardour-users] Ardour DAW - Hardware advice please..

[Joel White]

John Anderson wrote:

>
>
> Stay away from Adaptec SCSI controllers. They (or their drivers) are
> greedy about the PCI bus and cause xruns. I don't know about other SCSI
> controllers though.
>  
>

I was having xrun troubles on my system running a RAID using an Adaptec 
SCSI controller (onboard 7890).  I was about to come to the conclusion 
that the controller was the problem (I posted to the linux-audio-user 
list several times about this).  Recording to the SCSI RAID using Ardour 
and a Delta 1010LT (8 channels) in duplex mode generated xruns no matter 
what period (more at shorter latency, of course).  I ended up getting a 
Maxtor ATA drive to do audio work with, where I could record with far 
fewer xruns (but they were not completely eliminated).

Joel Roth suggested using ecasound to "simplify" the problem for 
testing.  To make a long story short, I could record 8 channels duplex 
and write the output at least twice with no xruns:

ecasound -r -b:128 -a:1,2,3 -f:32,8,48000 -i alsa,default \
-a:1 -f:f32_le,8,48000 -o output1.wav \
-a:2 -f:f32_le,8,48000 -o output2.wav \
-a:3 -f:32,2,48000 -erm:1 -erc:1,2 -ea:400 -o alsa,default

I could do the same using jack:

ecasound -a:1,2,3 -f:32,8,48000 -i jack_auto \
-a:1 -f:32,8,48000 -o output1.wav \
-a:2 -f:32,8,48000 -o output2.wav \
-a:3 -f:32,8,48000 -erm:1 -erc:1,2 -ea:400 -o jack_auto

Right after this, I built a newer version of Ardour (0.9beta19, from 
0.9beta11), and the number of xruns dropped dramatically.  To make 
another long story short (thanks to help from Paul Davis and other folks 
on ardour-dev), I traced the "problem" to the updates to the display 
during recording (the pinkish boxes that grow to the right while 
recording).  By commenting out one line of Ardour code that drew those 
boxes, I have no xruns while recording to the SCSI RAID, even at short 
periods (-p 256, even -p128 although I haven't tested this rigorously).

So, it turns out that the graphics card is the problem!  I'm running an 
older mobo with no AGP, so I use a PCI graphics card (S3-based).  I can 
demonstrate the problem simply by running x11perf with a test like 
-shmput500 while running one of the ecasound examples above - xruns like 
crazy!  Even recording to the ATA drive.  It is far worse using MTRR - I 
can get gobs of xruns from qjackctl with no clients running (i.e., not 
recording).

Bottom line: The Adaptec SCSI controller seems to work fine for audio, 
but may be prone to problems when other devices don't play nice on the 
PCI bus.  I've never had a problem with playback from the SCSI RAID, 
only recording.

Hope someone finds this info useful.  BTW, I'm quite happy with my 
system now (dual 600MHz PIII, 0.5 GB RAM, the aforementioned drives and 
sound card, running the 2.4.23 kernel with low-latency patch) - I can 
record 8 channels, and playback >12 tracks with plugins, with clocks to 
spare.

Joel

(Sorry that you get this twice, John - I meant to send it to the list)