[LAU] Fluidsynth, soundfonts, jack, and latency

Jonathan E. Brickman jeb at joshuacorps.org
Mon Nov 2 08:17:59 EST 2009

Guru, do you know what was/is the CPU load during the episode? 

> Hello everyone,
>   So I've been trying out AVLinux. By the looks of it, quite impressive 
> - but I soon ran into a rather serious issue, but I doubt whether it has 
> anything to do with AVLinux or not. I need your help in this knowing for 
> sure.
> My usual setup involves a piano sample on Linuxsampler and a strings 
> soundfont on qsynth. I had an unusual gig last week that required no 
> piano sounds, but instead use of multiple layered samples. I therefore 
> used only qsynth, with 3 engines running concurrently. So in my brand 
> new AVLinux setup, I loaded up my samples, and had sooperlooper running 
> 2-3 loops concurrently, all on a core2-duo macbook.
> Initially, all was ok. No noticeable latency, no xruns whatsoever.But 
> during the rehearsals, this happened: after sometime, specially at some 
> point when sooperlooper was running full steam, suddenly there was this 
> HUGE latency, coupled with lots of dropped notes. As in, I could hold 
> down a dozen keys simultaneously on the midi controller, and not all 
> notes could be heard; those that did, would  be heard  at various 
> instants upto about half a second later. Completely unuseable.
> This would persist even after restarting the jack server, but dissappear 
> on rebooting the OS.
> To me, what is scary and irksome, is not (only) that this glitch 
> happened consistently, but that there were no error messages in the 
> qjackctl window. No xruns. Nothing that suggested that something had 
> gone terribly wrong somewhere (which it had).
> I actually compromised on my gig sound, by offloading a lot of samples 
> what I wanted layered. I don't know if it was because of this, but I 
> didn't notice this particular issue on the gig itself (but it gave me 
> sleepless nights prior). But then, 5 mins before the start of the 
> program, I was left with no audio out of my system! (again, no error 
> messages). Restarted jack server, and everything back to normal.
> Again, no error messages/warnings. Not so much as a by-your-leave. ;)
> I'm now intent on finding the source of the problem. I'm looking for 
> pointers... where do I begin? Where's the 'smoking gun'?
> Thanks in advance!
> Cheers,
> Guru
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