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Ok, so you have installed the real time kernel form Planet CCRMA but you feel that something is still compromising your low latency objectives.  Well, this is touchy subject and it does have many variables, but with some research and some useful tools, you will gain the knowledge to have your Fedora machine running with acceptable latencies.
==Real Time Audio Production:Taking it a Step Further==


==Real Time Tests & Tools==
Ok, so you have installed a real time kernel and you are beginning to understand how it works, but you feel that something is still compromising your low latency objectives.  Maybe you are running JACK(JACK Audio Connection Kit) and you are experiencing an unusual amount of dropouts and inconsistencies.  Or, maybe you just want push the boundaries and determine the  lowest latency that is possible on your hardware.  Well, keep in mind that your latency is affected by everything from the cache in your CPU to the device driver for your sound card.  That said,  the following guide is intended to help you achieve minimal latencies with an acceptable amount of predictability.  This way, your computer will act as a tool for your audio production needs as opposed to a hindrance to your creativity.  
 
There are a two tools that I have found to use and further fine tune my system for real time audio use.


This first script was written and shown to me by raboof in the #opensourcemusicians channel on irc.freenode.net.
Note: If you are having trouble getting JACK Audio Connection Kit to start at all, try running it in Soft Mode.  Open JACK, look under Setup Parameters and put a check in the box to mark Soft Mode as being on.
This is the real time configuration quick scan.  You can download it here: http://code.google.com/p/realtimeconfigquickscan/  [http://code.google.com/p/realtimeconfigquickscan/]


Follow the instructions on the site.
==Checking Your Configuration==
 
This program was written by [http://arnout.engelen.eu/index.php/Main_Page Arnout Engelen].  


They are as follows
(Note to the wary):This program will '''only''' scan your computer for optimized real time settings.  It will '''not change''' anything on your computer.  It is also not necessary to have a real time kernel installed to run this script.   
   
You can download it from [http://code.google.com/p/realtimeconfigquickscan/ this link] and
follow the instructions on the site or you can use my instructions that are provided below.  Notice that my instructions will run the command line version as opposed to the GUI version and that the GUI version is still experimental. 
 
1. To install this program, you will need to install mercurial. So, from a terminal, do
<pre> su -c 'yum install mercurial'</pre>
 
2. Download the program:
<pre>hg clone https://realtimeconfigquickscan.googlecode.com/hg/ realtimeconfigquickscan</pre>
<pre>hg clone https://realtimeconfigquickscan.googlecode.com/hg/ realtimeconfigquickscan</pre>


simply navigate to the directory  
3. Navigate to the ~/realtimeconfigquickscan directory  
<pre>cd realtimeconfigquickscan</pre>  
<pre>cd realtimeconfigquickscan/</pre>  
for the last part I choose to run the command line version as I have had better luck with it.  Luck being results.
for the last part I choose to run the command line version as I have had better results with it.   
type <pre>./realTimeConfigQuickScan.pl</pre>  
 
4. So, type <pre>perl realTimeConfigQuickScan.pl</pre>  
and hit enter.
and hit enter.


Now, if the scan reports that something is not optimized, it will not only tell you what is wrong, but it will tell you how to fix it.  Upon running the script again, you will be able to tell if you made the changes correctly or not.  I encourage you to learn as much as you can about the things you choose to alter.  The more you understand, the more comfortable you will be while playing and composing music with your computer.
Granted, all of the tests in this scan may not apply to you and your hardware, but this is where the real fun begins.  And we all know that real fun can only happen in real time.
The very last thing you will likely see from the output of this scan is something like this <pre>** Set $SOUND_CARD_IRQ to the IRQ of your soundcard to enable more checks.
  Find your sound card's IRQ by looking at '/proc/interrupts' and lspci.</pre>
Do not be perturbed!
According to [http://arnout.engelen.eu/index.php/Main_Page Arnout Engelen], the writer of this script, this last part of the scan has only proved beneficial in one case and is not worth worrying about.  If you are interested in continuing in this direction, there is a nice script by the name of [http://ccrma.stanford.edu/planetccrma/mirror/fedora/linux/planetcore/13/x86_64/repoview/rtirq.html rtirq] that you can get from the Planet CCRMA repositories.  For more information on how that script works, I suggest visiting [http://subversion.ffado.org/wiki/IrqPriorities this website].
==On Benchmarking==
As I became more interested in the concepts of real time computing , I experimented with a few simple, yet interesting benchmark tests.  You may want to do the same.  However, be warned that the average benchmark test only tests the benchmark program itself, and our goal here is to make and/or record music using our computer.  These tests are super interesting, and you can find plenty of information about them at the  [https://rt.wiki.kernel.org/index.php/RT:Benchmarks RTwiki ].  For the most part, these tests are short and sweet and are a great way to begin learning about real time preemption.  I find the idea of splitting time up into nanoseconds very interesting and slightly incomprehensible.  But, to avoid digressing into another topic completely, your best benchmarking tool for audio purposes may be the JACK Audio Connection Kit using your preferred settings and applications.
==Real Time Computing Links==


As you can imagine, there are many uses for real time computing.  And let's face it, the computer doesn't care if it is processing music or not.  So, it becomes an issue of understanding how the kernel, the hardware, and the applications interact at the nanosecond level.  To save space and time, and to avoid repeating another wiki word for word, I will leave you with some links that further elaborate on the topic of a low latency performance objective.  After all, I am just the messenger.


Now, if the scan reports that something is not optimized, it will not only tell you, but it will give you a link to
* [https://rt.wiki.kernel.org/index.php/Main_Page RTwiki Homepage]
http://wiki.linuxmusicians.com/doku.php?id=system_configuration
* [http://subversion.ffado.org/wiki/IrqPriorities IRQ Priorities]
[http://wiki.linuxmusicians.com/doku.php?id=system_configuration]  
* [http://oreilly.com/catalog/linuxkernel/chapter/ch10.html Understanding the Linux Kernel:Chapter 10 Process Scheduling]


==Update==


Granted, all of the tests in this scan may not apply to you and your hardware, but this is where the real fun beginsAnd we all know that real fun can only happen in real time.
Lately, I have gone back to using nothing but guitar and amp.  I will reserve my knowledge of this genre for future uses and recordingi.e., my guitar playing needs improvement.

Latest revision as of 22:42, 9 March 2011

Real Time Audio Production:Taking it a Step Further

Ok, so you have installed a real time kernel and you are beginning to understand how it works, but you feel that something is still compromising your low latency objectives. Maybe you are running JACK(JACK Audio Connection Kit) and you are experiencing an unusual amount of dropouts and inconsistencies. Or, maybe you just want push the boundaries and determine the lowest latency that is possible on your hardware. Well, keep in mind that your latency is affected by everything from the cache in your CPU to the device driver for your sound card. That said, the following guide is intended to help you achieve minimal latencies with an acceptable amount of predictability. This way, your computer will act as a tool for your audio production needs as opposed to a hindrance to your creativity.

Note: If you are having trouble getting JACK Audio Connection Kit to start at all, try running it in Soft Mode. Open JACK, look under Setup Parameters and put a check in the box to mark Soft Mode as being on.

Checking Your Configuration

This program was written by Arnout Engelen.

(Note to the wary):This program will only scan your computer for optimized real time settings. It will not change anything on your computer. It is also not necessary to have a real time kernel installed to run this script.

You can download it from this link and follow the instructions on the site or you can use my instructions that are provided below. Notice that my instructions will run the command line version as opposed to the GUI version and that the GUI version is still experimental.

1. To install this program, you will need to install mercurial. So, from a terminal, do

 su -c 'yum install mercurial'

2. Download the program:

hg clone https://realtimeconfigquickscan.googlecode.com/hg/ realtimeconfigquickscan

3. Navigate to the ~/realtimeconfigquickscan directory

cd realtimeconfigquickscan/

for the last part I choose to run the command line version as I have had better results with it.

4. So, type

perl realTimeConfigQuickScan.pl

and hit enter.

Now, if the scan reports that something is not optimized, it will not only tell you what is wrong, but it will tell you how to fix it. Upon running the script again, you will be able to tell if you made the changes correctly or not. I encourage you to learn as much as you can about the things you choose to alter. The more you understand, the more comfortable you will be while playing and composing music with your computer.

Granted, all of the tests in this scan may not apply to you and your hardware, but this is where the real fun begins. And we all know that real fun can only happen in real time.

The very last thing you will likely see from the output of this scan is something like this

** Set $SOUND_CARD_IRQ to the IRQ of your soundcard to enable more checks.
   Find your sound card's IRQ by looking at '/proc/interrupts' and lspci.

Do not be perturbed! According to Arnout Engelen, the writer of this script, this last part of the scan has only proved beneficial in one case and is not worth worrying about. If you are interested in continuing in this direction, there is a nice script by the name of rtirq that you can get from the Planet CCRMA repositories. For more information on how that script works, I suggest visiting this website.

On Benchmarking

As I became more interested in the concepts of real time computing , I experimented with a few simple, yet interesting benchmark tests. You may want to do the same. However, be warned that the average benchmark test only tests the benchmark program itself, and our goal here is to make and/or record music using our computer. These tests are super interesting, and you can find plenty of information about them at the RTwiki . For the most part, these tests are short and sweet and are a great way to begin learning about real time preemption. I find the idea of splitting time up into nanoseconds very interesting and slightly incomprehensible. But, to avoid digressing into another topic completely, your best benchmarking tool for audio purposes may be the JACK Audio Connection Kit using your preferred settings and applications.

Real Time Computing Links

As you can imagine, there are many uses for real time computing. And let's face it, the computer doesn't care if it is processing music or not. So, it becomes an issue of understanding how the kernel, the hardware, and the applications interact at the nanosecond level. To save space and time, and to avoid repeating another wiki word for word, I will leave you with some links that further elaborate on the topic of a low latency performance objective. After all, I am just the messenger.

Update

Lately, I have gone back to using nothing but guitar and amp. I will reserve my knowledge of this genre for future uses and recording. i.e., my guitar playing needs improvement.