[LAU] xrun killer: --sync on jack2

[Jonathan E. Brickman]

To get jack2's sync mode through qjackctl, go to the Setup window, and 
add "-S" (capital S) to the end of the "Server Path" text.  It is 
important to not have extra spaces in that text, the server won't start 
if you do.

Your report is most interesting.  I am very glad to hear of ChickenSys 
Translator; if I ever need it, I'm buying it (I'll run it in a VM of 
course *grin*).  I do have to wonder about the crashing.  If the 
original SF2 was bad enough, it could crash fluidsynth quite easily, and 
at least in theory, the ChickenSys Translator could have translated the 
badness of the original SF2 over.  "Badness" could be many things; I 
have been lately studying a bit of what really can go into an SF2 (or a 
gig), and there's all sorts of transforms, effects, etc.  If the 
original SF2 was made with the wrong overabundance of that stuff, the 
process trying to play it (or the gig converted from it) would simply 
tie itself into a CPU-load knot and die, perhaps by trying to create too 
much simultaneity in reverb (for an oversimplified example).  And if 
anything Jackish fails in really the wrong way (CPU overload is often 
one way), it often takes Jack with it.  I would love to see an 
"auto-restart" in qjackctl :-)

But jack2 certainly is far more able to handle horsepower problems.  I 
am so happy it's in Debian Experimental!!!  I wonder if LinuxSampler is 
prepared to handle multi-CPU the way jack2 is?

J.E.B.

> Thanks Jonathan for the heads up on Jack2!
> A quick update:
> If you remember form my earlier posts (re: Fluidsynth, soundfonts, jack,
> and latency), I'd devised a "stress test", with the following results:
> (a) stable with a 1.6 GB piano sample in linuxsampler (b) promptly crash
> with a 8.2Mb string  soundfont with any fluidsynth-based  application.
> By crash, I mean jack requiring a restart, making things unusable for
> live performance.
>
> My strong suspicion was a bug with fluidsynth, to which I did receive
> helpful replies.
>
> Subsequently, I came across ChickenSys Translator, which can convert a
> soundfont to a gigastudio sample. I converted the same 8.2 Mb string sf2
> to a gig, and guess what - now with the same stress test, linuxsampler
> crashes jack!
>
> So the issue is not really with fluidsynth, but with jack itself. David
> had rightly suspected something to this effect, and Josh had suggested
> that Jack2 would be more resilient.
>
> I now believe the improved performance in my stress test when I upgraded
> jack was due to switching from jack to jack2. My system has subsequently
> become much more stable. I now need to try out the --synch mode in jack2.
>
> Quick question: How do I get into --synch mode using qjackctl?
> Looking forward to inputs/suggestions.
> Cheers,
>
> Guru
>
> [P.S. I hope I haven't hijacked the thread topic...]
>
>
> Jonathan E. Brickman wrote:
>    
>> I think I've got it :-)  Muchas gracias to Joakim Hernberg, who posted
>> the jack2 profiling document.  I read it about five times, trying to
>> ponder what my first step might be given that info.  It discusses two
>> major modes of jack2:  the default, which is asynchronous, and another,
>> which is synchronous.  Under asynch, my stress-test yields zero xruns
>> (or close) at 5.3 ms (as reported in Qjackctl); but under synch, my last
>> two tests say kosher at 0.667 ms *grin*  Shocking.  That synch makes a
>> whole lot of difference.  I can just imagine jack2 jockeying all four
>> CPUs to make that happen :-)  I'll be doing a lot more stress-testing to
>> prove it, but for right now, frames/period are 64, sample rate 192000,
>> two periods/buffer :-) :-)  I praise the Lord, and I thank everyone for
>> the help!
>>
>> J.E.B.
>> _______________________________________________
>> Linux-audio-user mailing list
>> Linux-audio-user at lists.linuxaudio.org
>> http://lists.linuxaudio.org/mailman/listinfo/linux-audio-user
>>
>>
>>      
>
>