Pipewire pro audio

qk4-li3

Reporting my experiences.

pipewire-jack: installed.
configurations, regarding automatic switching to the appropriate sample rate for the project: done.
pavucontrol: installed, pro-audio profile selected for main USB-audio interface. Other soundcard profiles Off (Intel HDA, HDMI, etc).
other linux-audio related software installed: QjackCtl, jack-audio-connection-kit, jack-audio-connection-kit-server, pulseaudio-module-jack

With Guitarix, there's *x-runs even at default (1024) buffer size, which is way too large buffer to begin with.
*x-runs are buffer over or under runs which affects sound to stutter.
feel free to suggest something...

RegularJogger

Have you tried switching your CPU scaling governor to performance prior to running Guitarix?

I switched to PipeWire way before it became default in Solus specifically because I didn't want to bother myself with setting up JACK anymore and honestly it's been smooth sailing since then (so far no real issues or xruns even at buffer size 64, though I've been using 128 lately).

Frankly, I didn't even change any configuration nor do I switch any audio profiles (really just using my Yamaha THR as both audio interface and monitor for guitar playing/practice and stuff). Couple things I do before running any audio app though:

Change my CPU scaling governor to performance.
Run from terminal with PIPEWIRE_LATENCY="128/48000" (which is your desired buffersize/samplerate).

Regarding the CPU governor (personally have aliases for this stuff and the pipewire latency in my .bashrc):

To check which governor is your CPU set to currently: cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor

To actually change the governor use the cpupower utility which you can get by installing the linux-tools-cpupower package.

Then sudo cpupower frequency-set --governor performance to change the governor to performance mode.
And sudo cpupower frequency-set --governor powersave when you're done to set it back to powersave.

qk4-li3

RegularJogger Just quick reply just before I have to go.
Good suggestion otherwise, but my cpu is locked @2,4GHz from BIOS if I recall correctly. It's desktop not laptop. So cat /sys/devices/system/cpu/cpu/cpufreq/scaling_governor gives me cat: '/sys/devices/system/cpu/cpu/cpufreq/scaling_governor': No such file or directory
So It's four physical cores full on @2,4GHz all the time. I think there's no throttling issues then.
With laptop your instructions are very helpful for sure.

RegularJogger

qk4-li3 You're missing an asterisk from the command to check your CPU scaling governor, that's why you get that No such file or directory error (that asterisk is a substitute for core numbers, that way you check all of them).

My machine's also a desktop and there's noticeable difference when switching the governor. Not sure what my CPU settings in BIOS are right now regarding throttling (altough there's definitely some as HTOP shows my cores starting at around 800MHz under no significant load) etc. though and I'm too lazy to reboot and check now... 😅

qk4-li3

RegularJogger You're missing an asterisk from the command to check your CPU scaling governor, that's why you get that No such file or directory error (that asterisk is a substitute for core numbers, that way you check all of them).

This time with copy-paste. Same result.
when I copied text here it removed asterisk, but it was there.
No such directory, see:

RegularJogger

qk4-li3 Ah, so that's also ruled out... No other idea what may be the culprit to your issues with PipeWire then, sorry. 🙁

Hopefully someone more knowledgeable chimes in...

qk4-li3

RegularJogger This kind of troubleshooting requires ruling out things and checklists. We just ruled out one thing. Your contribution didn't go to waste and is appreciated. Making sure it's not cpu scaling/throttling will certainly help everyone with "modern" power management on their machine. Your advice wasn't outdated. It's more relevant today more than ever. Cheers!

qk4-li3

In the meantime let's see if next Solus update changes anything. There was something concerning linux-audio, didn't inspect them too much, let's see where it goes.

qk4-li3

Problem not solved, bad cracking in sound remains.
What would be next thing to check?

qk4-li3

I find this strange:
I launch QjackCtl, then I launch Guitarix. I strum guitar strings. Sound is crackling. I stop and quit QjackCtl. Guitarix remains running. Crackling sound stil comes through Guitarix, even if I just stopped and quit QjackCtl. I can't see anything jack related process from System Monitor while Guitarix is still showing appropriate jack ports ticked. Isn't something wrong with that? I would expect to see some jack process in System Monitor. Really confusing!

plutuplutu

Do you have realtime checked in qjackctl settings?
You don't see jackd because pipewire is the sound server.

qk4-li3

plutuplutu Yes, there's realtime tick box which is ticked in QjackCtl. Also QjackCtl's "display" indicates Active "RT" (flashing) and about 87% - 2000% DSP load.

qk4-li3

plutuplutu You don't see jackd because pipewire is the sound server

Ok, I thought pipewire should become jack's client.

qk4-li3

I managed to install this analysis software: https://codeberg.org/rtcqs/rtcqs
It gives me this error: Could not find kernel configuration.

What would that mean then? Their Wiki is empty. Anyone familiar with this tool?

plutuplutu

Apparently, jack can be started even if you have pw. Have you tried this?
https://discussion.fedoraproject.org/t/realtime-priorities-for-jack-vs-pipewire/105188/4

qk4-li3

plutuplutu Great find, thank you!
No I haven't tried that but I will try that next.
One thing I never remember: There are two tick box options in QjackCtl. 1. Enable D-Bus interface 2. Enable JACK D-Bus interface. Which one or both enabled? I'd guess nr.2 enabled in this case, and nr.1 is for QjackCtl itself (something like that?) and for other(?) reasons than starting jack server. Please correct me if I'm wrong.

qk4-li3

plutuplutu I can now report that, no, that didn't fix it.

Axios

Dunno if this is of any help https://medium.com/@margitai.i/how-to-set-up-an-open-source-guitar-rig-on-linux-5a5cce7bd916
Maybe you missed something

qk4-li3

Axios Thanks for suggestion. Unfortunately those instructions are outdated. They don't work anymore because of Pipewire. For example setting buffer size via QjackCtl is impossible. There's some info regarding D-Bus though, that could be relevant also with pipewire (like suggested in @plutuplutu 's link), I guess. I don't know!

qk4-li3

For anyone who may be interested in low-latency audio issues with Solus & pipewire, here's sequel to previous.

Things that I've tweaked since last post:

Set kernel parameters preempt=full threadirqs mitigations=off

I've added the parameters following these *instructions:
https://help.getsol.us/docs/user/quick-start/boot-management

*I happened to notice (!), that this procedure is little different in Solus, compared to usual GRUB modification instructions, which one can find for example at debian/ubuntu forums.

Sources of advice (for me to try these things):

https://gitlab.freedesktop.org/pipewire/pipewire/-/wikis/Performance-tuning#kernel
https://wiki.linuxaudio.org/wiki/system_configuration#:~:text=Using%20the%20threadirqs%20kernel%20option
https://wiki.linuxaudio.org/wiki/system_configuration#:~:text=Disabling%20Spectre%20and%20Meltdown%20mitigations

Results: There was notable improvements, but still not enough. For example, I don't notice broken sound anymore while watching/listening online content. With guitarix, I can now lower the latency to 256 and sound is borderlining broken/solid. Previously at 256 it was garbled mess.
Aim here would be under or no more than 10 ms round trip latency with pristine sound quality.
So, "Close, but no cigar". There must be some fundamental things still wrong with pipewire and I guess that makes waiting for updates like waiting for Christmas.