[PlanetCCRMA] Fedora 20 3.12.12-300.rt19.1 with Focusrite Saffire Pro40

Donald Steven t6sn7gt at aim.com
Thu Aug 28 04:29:33 PDT 2014

Thanks Tony.  This is great!



On 08/23/2014 11:56 AM, Tony White wrote:
> Hi Don,
> You should use 48000 sample rate. It is jack's default rate, the 
> recording studio standard and the most tested.
> Starting with 256 frames 48000 and 2 periods is a good starting 
> setting. If using that produces no xruns then try 128 frames 48000 and 
> 2 or 3 periods next. Then if that produces no xruns, you can go lower.
> Preempt (low latency)... False
> realTimeConfigQuickScan does this too. I guess that it is because the 
> script is being run by a user that does not have the access level 
> required to probe for that. Best not run that test script as root 
> though. If you have booted kernel-rt (uname -a in a console) then you 
> have low latency. The script just does not try to detect it correctly.
> You should add your user account to both the audio and jackuser 
> groups.  (su -c 'yum install system-config-users') The program 
> system-config-users will appear in the desktop menu under the 
> administration section afterwards allowing you to do so easily.
> Be sure to add the threadirqs kernel parameter to the kernel-rt boot 
> entry option in grub.cfg.
> Install the package rtirq and enable it with: su -c 'yum install rtirq 
> && sytemctl enable rtirq'
> Edit rtirq so that  your sound card's irq is a high priority and not 
> threaded by adding it to RTIRQ_NAME_LIST and RTIRQ_NON_THREADED in 
> rtirq, set limits for the audio and jackuser groups in 
> /etc/security/limits.d/. You set the jackuser group to have a slightly 
> lower rtprio set than the rtprio set for the audio group. 
> http://subversion.ffado.org/wiki/IrqPriorities
> Set the cpupower governor to performance: su -c 'cpupower 
> frequency-set --governor performance' You need to do this every boot. 
> You could create a systemd unit to do this for you along with any 
> other real time settings you want to be set every boot. (Otherwise 
> create a script and run it by hand.)
> Install and run realTimeConfigQuickScan
> su -c 'yum install realTimeConfigQuickScan'
> Run /usr/bin/realTimeConfigQuickScan in a console and fix any issues 
> it exposes. Run it again after you have fixed any issues to be sure.
> Disable any services you do not require but be careful not to disable 
> any important system services su -c 'yum install 
> system-config-services' to monitor and manipulate services (Referred 
> to as systemd units.)
> Having looked into systemd quite deeply, systemd units which run from 
> the timer targets can cause random xruns if they are not set to a low 
> priority. Nice=19 IOSchedulingClass=idle IOSchedulingPriority=7 
> CPUSchedulingPolicy=idle is the kind of stuff I am trying out in 
> systemd units that I have created and I have added to the timers 
> target. Might be over kill. Completely disabling them and manually 
> running them may be a better solution.
> Consider turning off the wireless card on your laptop if it has one. 
> They are notorious for causing xruns. Alternatively, set's the 
> wireless card's driver irq to a priority just below your sound card 
> driver in rtirq and also add it to the RTIRQ_NON_THREADED list.
> I don't have any experience of firewire interfaces but if you set the 
> things mentioned above, you should hopefully achieve some level of 
> success. Zero xruns is definitely possible.
> Hope this helps.
> Kind Regards,
> Tony
> --
> Tony White
> twhite at operamail.com <mailto:twhite at operamail.com>
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