User:Tertl3/real-time

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. This test will scan your system and perform a number of checks. The checks are 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 first program was shown to me by Arnout Engelen. As far as I know, he wrote this program without any help.

(Note to the wary):This program will only scan your computer for optimized real time settings. It will not change anything on your computer.

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.

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

 su -c 'yum install mercurial'

1. Download the program:

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

2. 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.

3.So, type

./realTimeConfigQuickScan.pl

and hit enter.

Now, if the scan reports that something is not optimized, it will not only tell you, but it will give you a link to the linux musician's wiki which has detailed information about the many checks that are performed with this program. 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 checking out 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 shell scripting in general. 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 different 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.

• RTwiki Homepage
• IRQ Priorities
• Understanding the Linux Kernel:Chapter 10 Process Scheduling