Question about DSP and Xruns

Hello all.

Sorry if this is a dimwitted question but here it is; Whenever I go above about 65% DSP I start getting Xruns (this is when mixing once all recording is done). Some of the Xruns get marked on the display with the yellow marker of doom (but are’mt audible) and some noises/glitches appear but dont get marked. So, my questions:

  1. Why does it start to crack up at what seems like a modest DSP%? I would expect it if I was up near 90% but 65% seems kinda low. Is this something to do with the interface to my soundcard?

  2. Why do the non-audible Xruns get marked but not the audible ones? I should point out the audible ones dont appear in the same place each time - they appear randomly.

For info I am using an i5 2500K (not OC’d at the moment) and I have ardour set to use all but 1 core for DSP.

I suspect I know the advice people would recomend to solve the issue; (a) record tracks better so I dont need so many plugins to retrospectively try and tidy up; and (b) bounce tracks and remove the originals.

Both of these are good solutions if you have the skill (which I really dont). I’m a hobbyist with little musical or technical skill so I need all the options I can get during mixing :wink:


The reasons for xruns and other glitches are many and varied, and almost always system specific in some way, so its very difficult to advise any kind of ‘cure all’ solution without knowing the specifics of plugins, session, audio interface etc, and even then it may not be possible to pin it down to one cause, more likely its an interaction of several things, each of which on their own is not a problem. However, the general advice is, increase audio buffer sizes (in your JACK settings) - you can do this only when mixing if the added latency causes problems during recording. Increased buffer settings will also reduce your DSP usage. Select an appropriate sample rate, if for example you are using 96K you will have higher DSP usage, so you could try 44.1 or 48K (if you use properly designed plugins and processing, there is almost no audible benefit to using higher sample rates)
The DSP load is an average, poorly designed plugins - or a bug in the plugin processing - may “spike” the CPU usage at odd times and cause xruns, while the average still appears to be low.

Also make sure your system is set up for realtime preemption, not sure what OS you are on, but since you described A3 I assume Linux right now. Most systems are not set up properly out of the box to support this, but distributions intended for audio (Like AVLinux) can be. Since you are getting xruns at moderate DSP levels, this is where I would look first.



I forgot about my frames/periods - was still set to 256 for latency. Increasing to 512 has given me more room again. Thanks for the reminder linuxdsp! My main reason for asking was to see if there was anything obviously wrong with my set up that was causing it to happen at what appeared to be modest DSP usage. I guess it doesnt really matter why the xruns are happening as long as I can avoid them ruining my audio.

Seablade - I am using Tango Studio and I am fully set up for realtime (this OS install is separate from my normal OS and only used for audio).

To be fair to the system, I shouldnt really complain. I just did a quick tot up and I have 45 tracks in this session with at least 2 plugins on each (some have 5 plugins on). So I suppose it is being worked pretty hard.

Thanks for the info.

that is a lot of processing so i guess your system is coping very well.

Another thing you can dow is bounce tracks with processing to free up some system resources, though you have to be happy with any of the tracks you are bouncing.

im running a on an athlon 2ghz dual core and struggle with 8 tracks with plugins on every track (some just a few other with upto 5)

If your using pitchshifters, those i have found to really cause issues