Improving playback performance??

I’m getting alot of clicks (dropped samples basically on playback) either when jack realtime setting is turned on or off. Recording (thou not thoroughly tested) seems to be unaffected.

My system is as follows:
M-Audio Delta 44
Athlon XP2000+, 1GB pc2700 ram, 2x133ATA HDD’s, Fedora Core 5, Vanilla Kernel with preemtive scheduling, jack 0.100.1, and ardour version 0.99 (not sure what sub version, but it’s the fc4 ccrma rpm).

I have just recently shifted from a cubase sx winxp system, to a purely open source system, so i have a vague idea of what sort of performance i can get out of my hardware. What I would do in cubase, would be kill everything (even explorer.exe) minus what was the bare minimum, kill all effects and/or plugins and i’d get glitch free playback and recording for (test up to) about 16 tracks, recording up to 4 at a time, at 88.2khz, 24bit. I’d then tend mix with processer heavy effects after all the recording was done, and i would get some glitches, but minor ones, and they wouldn’t be on a mixdown anyway.

What I’m getting at the moment, is alot of glitches on playing. Baring in mind i’ve only shutdown a few of the standard process/services in a fedora/gnome session. Gnome itself is still running. With jack realtime set, I’d also be getting glitches in the mixdowns, at a varying frequence depending what the latency was set to inside ardour. With realtime switched off, it mixes down perfectly, but playback hasn’t really changed.

I have only really tested this system doing mixing at the moment, recording a few seconds here and there to see if recording was working, and from what i can tell the recording is glitch free anyway. It’s just a audioable eyesaw to be mixing with so many glitches.

When i setup my system i had kept the original kernel (Fedora Core 3) and added the low latency kernel. One time i had booted from the stock kernel and started getting a ton of xruns (glitches/dropped data). For starters, you may want to apply the low latency patch to your kernel and see if that fixes things. ( see ).

Im currently running a Celeron 1 Ghz with 1.2 Gig RAM and can record 8 channels of 24/96 w/o any xruns, so im pretty sure that your gear is fast enough.

Another question, what type of Motherboard do you have? Does it use the VIA chipset?


did you set a shared memory for jack? it could be jack use the /tmp directory and this not good.

yeah, it is a asus avk777 (i think thats what it’s called), that uses the via chipset. is this a bad thing?

there are a lot of variable experiences with VIA chipsets, not all bad. I have a VIA chipset on my motherboard for an Athlon XP 1800 processor, and it works fine for me.

however, i’ve recently been having loads of xruns at 1 or 2 second intervals when under load (i.e. ardour with a session open). i eventually found out that a USB2 interface card i’d recently added was sharing IRQ 3 with my sound card.

after swapping the physical locations of the cards in the PCI slots, my sound card (a m-audio delta 66) regained sole use of IRQ 3 which fixed all my problems.

you can see what uses each IRQ by typing

cat /proc/interrupts

in a console.


i’ve vastly improved all aspects of my system. noting the via chipset problem, i have alot of hassle with that chip along with USB under windows, which was also on the same IRQ as the delta.

so i’ve recompiled removing some of the drivers i don’t need for audio creation (wireless - doesn’t work anyone, and firewire) to improve bus speed; patch the kernel with the realtime patch; and tweaked with pci latency a little (i don’t know how much good this actually does.

if i reset xrun count after opening everything i need, i (sometimes) can get a whole 16 mono channel mix without any xruns ported through jamin. bypassing jamin i get better results.

so i’m guessing this is the best performance i can get, at least with my system.