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

[David Jones]

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?

Glad you found a solution!

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