[LAU] [SOLVED] "Skewed" Audio with JACK

[David Jones]

On Dec 7, 2016 10:52, termtech <termtech at rogers.com> wrote:
>
> On Wednesday, December 7, 2016 10:43:22 AM EST David Jones wrote: 
> > On Dec 7, 2016 06:48, termtech <termtech at rogers.com> wrote: 
> > > On Wednesday, December 7, 2016 7:34:25 AM EST David Klann wrote: 
> > > > On 12/03/2016 01:50 PM, termtech wrote: 
> > > > > On Saturday, December 3, 2016 1:20:09 PM EST David Klann wrote: 
> > > > >> Greetings, 
> > > > >> 
> > > > >> Long-time Linux user, and relatively new JACK user here. I have built 
> > > > >> ... 
> > > > > 
> > > > > Hello, this might be a long shot, but maybe not. 
> > > > > You mentioned it did this when Jack was disabled, 
> > > > > 
> > > > >  so it seems Jack is not the problem. 
> > > > > 
> > > > > Look for the LAU thread on Wednesday titled: 
> > > > > "[LAU] [SOLVED] Crackles in audio, drifting intermittent noise etc." 
> > > > > I was having very strange phasing problems, although I didn't notice 
> > > > > 
> > > > >  from channel to channel but I wasn't really listening for that. 
> > > > > 
> > > > > I knew it was hardware related, only that could cause it. 
> > > > > 
> > > > > My ONLY solution was changing the number of enabled CPU cores, 
> > > > > 
> > > > >  either through my BIOS or through Linux commands such as: 
> > > > > echo 0| sudo tee /sys/devices/system/cpu/cpu3/online 
> > > > > cat /sys/devices/system/cpu/cpu3/online 
> > > > > 
> > > > > I found that I must run with just ONE core for the most stability. 
> > > > > (I had posted that I found TWO cores were OK but actually 
> > > > > 
> > > > >  further test revealed it was not OK.) 
> > > > > 
> > > > > So try: 
> > > > > echo 0| sudo tee /sys/devices/system/cpu/cpu1/online 
> > > > > echo 0| sudo tee /sys/devices/system/cpu/cpu2/online 
> > > > > echo 0| sudo tee /sys/devices/system/cpu/cpu3/online 
> > > > > 
> > > > > cpu0 will always be online. 
> > > > > 
> > > > > Tim. 
> > > > 
> > > > Hi Tim! 
> > > > 
> > > > Thanks for this tip! I probably never would have considered this even 
> > > > though it was a vague, nagging thought in the back of my head. 
> > > > 
> > > > Disabling three of the four cores (or hyperthreads?) on the CPU fixed 
> > > > the problem for us! 
> > > > 
> > > > Specifically (and to tweak your command set), I placed the following in 
> > > > /etc/rc.local to ensure the CPU disabling survives a reboot: 
> > > > 
> > > > <code> 
> > > > for c in 1 2 3; do echo 0 > /sys/devices/system/cpu/cpu${c}/online; done 
> > > > </code> 
> > > > 
> > > > In reading the "Crackles in audio..." thread, I am curious to know why 
> > > > this happens with some CPUs and not with others. My understanding is 
> > > > that this is fundamentally a timing issue between processes that are 
> > > > running on different CPUs (or cores). So, while it's not specifically a 
> > > > JACK issue, if the jackd process is running on CPU0 and the audacity 
> > > > process is running on CPU3 then a timing error may be introduced between 
> > > > those two CPU's. Is that a reasonable summary of the effect? 
> > > > 
> > > > And for my next trick, I will experiment with the taskset(1) command to 
> > > > set processor affinity for the audio processes. Maybe we can leave all 
> > > > four CPU's enabled and still avoid the "left-right channel skew" 
> > > > problem. 
> > > 
> > > Ah thanks, I was looking for something like taskset. 
> > > I wondered if the entire audio chain, from driver to application, 
> > > should somehow be set to one CPU even if all four are enabled. 
> > > Please let us know how it works out for you. 
> > > 
> > > I am very late to this multi-core party. It's my first such PC. 
> > > I am sure this episode has been repeated before in other threads. 
> > > It's hard to dig through the confusion and misinformation. 
> > > Even though I did research these CPUs before buying, I didn't 
> > > expect it would affect things in this manner. 
> > > 
> > > Tim. 
> > > 
> > > > Thank you everyone who weighed in on this, and especially Paul for 
> > > > pointing out that it cannot be an issue introduced by JACK. 
> > > > 
> > > > Best regards, 
> > > > 
> > > >   ~David Klann 
> > 
> > Well, I have 2 PCs I do audio on. One has 4-core AMD Phenom II (no 
> > hyperthreading). Other has Intel i7 (4 cores + hyperthreading). Have never 
> > tweaked anything like what you're talking about and have never had any such 
> > problem as you had. 
> > 
> > I do not have Pulseaudio installed on either of them. 
> > 
> > My final guess at root of problem: hardware issue with CPU itself. Maybe 
> > some manufacturing defect that only manifests when all cores are in use? 
>
> It appears to be something related to certain (older?) PCI audio cards. 
> Although, I think Len said he's running a similar card as mine 
> and hasn't seen any problems. 
>
> An older SBLive! PCI card appeared to work fine. Maybe I should test again... 
>
> Tim. 

Never had it when I used an AudioPhile 2496 PCI card, either, on the AMD machine. The i7's in a laptop, so limited only to internal audio or external USB audio.

David W. Jones
gnome at hawaii.rr.com
authenticity, honesty, community
http://dancingtreefrog.com