DSP spikes no plugins Linux latest ardour Linux

Just wondering what could cause DSP spikes when just importing raw tracks with no plugins. I’m on 4096 buffer snd dsp is like 1 percent to 3 and then 16 then back down. It’s not a big issue just wondering what could cause that.

I’m using a lll my cpus in settings and high performance mode on my workstation.

Is there anything I can adjust in settings to make things more stable.

I was previously on a session at 96k with minimal plugins and dsp would go into the 60s etc snd I would be worried since when I start mixing if it will t worse even at higher buffer settings. Think it was 2084 at that time.

Did you try if you got the same kind or amount of peak with “all but one CPU” in settings?

That is a strong indication that every now and then some hardware devices hogs the bus for a long time, and prevents the CPU from using the soundcard.

Some WiFi chipsets are known to do that, or some system health checks (SMI) or power-management could be responsible.

Try turning off WiFi, ensure that IRQ priorities (rtirq) are set to prioritize the soundcard, perhaps try a realtime-kernel…

see also The Ardour Manual

Haven’t tried that, I may see how that turns out

Oh ok I’ll check the wifi as well

I had something similar which turned out to be because in Ardour’s ALSA settings I had accidentally selected ‘default’ for the ALSA interface. ‘default’ was / is actually not a real audio interface, but, instead Pulseaudio pretending to be an ALSA interface. Because of the way pulse does what it does this caused erratic latency variations and DSP demand spikes. Switching instead to the real audio interface solved the problem.

Interesting. This should not be possible, by default Ardour ALSA only lists hardware devices with a hw:<num>,<num> identifier.

Are you perhaps using Ardour/JACK + JACK/ALSA?

Interesting, I’ll check how it is with jack vs Alsa as well

Keep in mind that JACK report average load (and may smooth over short spikes).

Since Ardour 6.8 you can look at Menu > Window > Performance Meters for a reliable, backend independent report.

I wasn’t using JACK at all. Perhaps I’m mistaken, I was sure that was the reason. I definitely had DSP spikes with no plug-ins, just a basic audio track - in that case I can’t remember what was the cause, or, maybe I just reverted to an earlier version for the testing I wanted to do.

When I used jack the dsp in ardour was more stable. I tried with wifi off in alsa and it was acting the same. But with wifi on jack was still stable.

I will use jack if I have any issues with dsp. Still not sure why. Does jack smooth out the spikes, is that why it appears better.

Don’t yet yourself be fooled by the DSP load that JACK reports to Ardour. JACK just reports the average, it smoothes away, even ignores, outliers.

Yes. Check Window > Performance Meters for reliable comparison.

In general you’re better off without JACK, that has additional overhead and also timing issues with MIDI.

I didn’t know about the MIDI issues with JACK. What is it exactly? And do you know if that will be fixed by pipewire?

Oh ic, the DSP does look very convincing, I guess I’ll try to see how to see why alsa is acting up.

Jitter (inaccurate timing), it’s specific to jack2 (and ancient versions of jack1), see Ardour Manual | MIDI on Linux for details.

As far as I know, pipewire is not affected.

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