Improve audio quality free ($0)

[dpaws]

At the moment I have Vortexbox installed on my new server and all is well, the VB wiki walk through guides have proven fairly fool proof and reliable so far. Unfortunately I still have to switch between the Vortexbox player and Squeezeplay depending on what I want to do (gapless/hirez/sync) but no great hardship involved.

I am now interested in optimising the playback from both of these applications to achieve a quality comparable with the Jplay plugins that I've used previously. I had a look at the guide above and its complication switched me off - I don't wish to download from another repository let alone write long scripts to ensure that the settings boot up from start up each time - this is the 21st century after all, I'd left all that behind with my TRS-80!

Is there no way that these latency and real time kernels can be built in to the set up options of the two aforementioned players? Even into the control panel of vortexbox itself? The Chrome interface for VB is excellent, this would appear to be the optimal place for such a control panel option....

Please guys?

[andrew]

Our testing has shown that real time kernels do not improve the sound so you can save yourself the trouble. Also there should be no reason to use squeezeplay now that VortexBox Player can do gapless playback.

[wvanbakel]

I am now interested in optimising the playback from both of these applications to achieve a quality comparable with the Jplay plugins that I've used previously.

Just the other day I found information that suggests that the current kernel, used by VortexBox, offers the realtime features that were not available in older kernels:

Kernels >= 2.6.31 seem to work pretty good without RT patch, also for real-time pro audio usage. It's not strictly necessary anymore to install a real-time ('rt') kernel to get good results. Although the best results are still expected when using a real-time kernel. Try it, test it and decide for yourself.
In the pre-2.6.39 kernel era rt kernels were indeed necessary in some cases where sound devices were sharing IRQ's with other peripherals. With the rt kernel and the rtirq script you could prioritize IRQ threads but since 2.6.39 it is possible to use the rtirq kernel with a generic kernel and the threadirqs kernel option.

Source : http://wiki.linuxmusicians.com/doku....210dcdf2cc362c

However, I do notice a difference when I apply a few modifications:

/etc/sysctl.conf:

vm.swappiness = 10
fs.inotify.max_user_watches = 524288

/etc/security/limits.conf:

@audio - rtprio      90
@audio - memlock     512000
@audio - nice        -19

/usr/local/sbin/network_up.sh:

/usr/bin/chrt -f -p 99 $(/usr/bin/pgrep softirq)

These are only a few lines to edit.

[andrew]

Yes VortexBox has been using the newer kernel for about 2 years. So RT is not necessary.

Do you have the source for what your other tweaks do for audio? I can't imagine how they would help. For example setting vm.swappiness = 10 changes how the kernel swaps to disk. ANY swapping to disc is really bad and will effect many things including audio. VortexBox is designed never to swap to disk unless there is a problem with your system.

fs.inotify.max_user_watches change the max files that can be watched. If your system is watching that many you will have a system slowdown. Your other tweak seems to give the soft irq process more priority. But this process already has a very high priority so I'm not sure how this will help.

[wvanbakel]

Do you have the source for what your other tweaks do for audio?

vm.swappiness = 10:

This setting changes the so-called swappiness of your system, or in other words, the moment when your system starts to use its swap partition. You can check the current value with cat /proc/sys/vm/swappiness, in most cases it is set to 60. This is too high, it will make your system start using swap too fast which might influence the overall performance.

Source: http://wiki.linuxmusicians.com/doku....al-time_kernel

inotify max_user_watches = 524288:

There are references on the net on adjusting the fs.inotify.max_user_watches value also for enhanced performance. But it remains very unclear where these references come from and if adjusting this value actually does anything at all.

Source: http://wiki.linuxmusicians.com/doku....al-time_kernel

I ran the perl script realtimeconfigquickscan and adjusted the settings according to the output

I also mount the file systems with noatime:

Setting the noatime parameter in your /etc/fstab file reduces the amount of disk I/O (the inode access times are not updated each time a file is read) which could improve the overall performance of your system.

Source: http://wiki.linuxmusicians.com/doku....al-time_kernel

Also: http://fedoraproject.org/wiki/Docume...Time_Utilities