Pops and crackles when recording live from LMMS

Having trouble with LMMS? Ask about it here.
I've also posted this to linuxmusicians.com as well, but I thought I'd post here too as this seems to be LMMS specific - although it could be Carla, but the guys there are probably way too busy to respond to my weird problems.

I'm recording LMMS live (a number of a reasons why, not least of which the Stochas sequencer won't render out notes in LMMS for some reason, which is also unknown to the developers).

I'm getting the occasional loud pop or crackle randomly during playback. I'm assuming that it's the CPU, but it could be something else too which is why I'm asking here. Unfortunately, I'm not going for the lofi sound :D

I have set the LMMS buffer to its very maximum.
I'm resisting using any synths that might be heavier on the processor (Vital, Surge, Odin2)
i have set the CPU governor to performance on all 8 cores.

I'm running two instances of Stochas in Carla within LMMS, six instances of Synth1 (obviously using the Wine bridge), one instance of Decent Sampler and two instances of Valhalla Supermassive (again, wine bridge).

The machine I'm running it on is a little "mature", but should still be quite capable:

HP z240 Workstation; 7th Generation core i7; 16GB RAM; NVMe SSD with plenty of space.
The audio is going through an nvidia K620 card (I realise this probably makes no difference but I thought I'd mention it).
I'm running stock Kubuntu 22.04 minimal install (compositor is OFF) with nothing else installed but LMMS and associated plugins/synths/effects. ALL background services are switched off.

When playing back, the CPU is running somewhere between 30%-40%

I'm recording through sox, but the popping happens whether I'm recording or not.

Does anyone have any ideas if there's anything I can do to fix this? This is driving me insane. Thousands of gamers livestream stuff way more processor intensive than this and often on lesser hardware. What am I do wrong?
Stochas wont run through Vestige ? (The windows version)

Install it with wine, and then search the .dll file.

I had ample guitar working like that.

The path had home/.wine/ in it,
Stochas is a VST3 which LMMS doesn't natively support. Additionally I've tried various sequencers in LMMS and there's simply no way to drive an instrument like that.
DaveAmbient wrote:
Sat Feb 11, 2023 7:13 am
I'm getting the occasional loud pop or crackle randomly during playback
You ned to isolate it, and that is unfortunately not a simple task.
The reason is that even though a track is muted, it will still put the same load on the CPU, as when t was unmuted.
So you can try to work with two instances of lmms, and see if you can isolate the issue, if not you have to go through a painstaking process where you remove parts and reinstall them for then removing yet an other part...
It is horrible to do, but alas only way..
But you should be able to shortcut this path..
Synth1 is ridiculous lean on the cpu, there is almost no influence, so it would be odd if synth1 is the reason -Unless! You have added effects on the FX-tab!
effects are often the reason for having issues, and they can be subtracted from lmms by a mute!
That would be the first thing i would go through: All effect on FX-tabs either in instruments, or in mixer.
After that i would look at the heaviest VST, that could be that Stochas-thing..
I have created pieces that use very heavy synths and effects and they do end up stuttering with processor overload. But just using very light synths still produces the popping. The only success I had was where I was using one LMMS track hosting carla patchbay containing 3 instances of synth1. That produced no popping, but I couldn't do much with that for this project.

So I think, yes, we can discount Synth1 as being the problem here.

I never use the FX tab. All effects are either in the mixer or, more recently, I've been adding them in Carla patchbay itself where I can control them a bit better. Generally my use of effects is quite low - usually Valhalla Supermassive, a simple delay like the one from Kilohearts, and a couple of filters, also from Kilohearts.

The issues seem to begin when I add a second Carla patchbay track in LMMS. But, like you say, that might be a red herring and it could be down to what i've got running in those tracks and there may be plugins that don't like each other. And I do need to go through them painstakingly one by one to see if removing any solves the problem *sigh*.

Unfortunately, if it does turn out to be Stochas that brings this entire project to a stop. The probability element is essential.