ECE497 Notes on Rakarrack

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Rakarrack is an open source effects processor that emulates a guitar effects pedal board. It can be run easily in Ubuntu on the BeagleBone. Below is the installation process for use with the BeagleBone Audio Cape.

  • Note: The following is tested on Ubuntu 12.10 running version 3.2.33-psp26 of the kernel.

Ubuntu Installation

To install Ubuntu on the BeagleBone follow the instructions found on the BeagleBoardUbuntu elinux site.

 login: ubuntu
 password: temppwd

Run `sudo apt-get update` and `sudo apt-get upgrade` until there are no more updates/upgrades to install.


In Ubuntu, to get ALSA to work with the BeagleBone Audio cape, the following modules need to be specified in '/etc/modules'


You can test the audio by running `speaker-test`. Also running `aplay -l` will show a list of available sound cards. If the sound card is not shown, run `lsmod` and `dmesg` and make sure the kernel modules above have loaded without errors.

Rakarrack Installation

Rakarrack uses the Jack Audio Connection Kit to route audio between applications.


Start by installing jackd2. This requires a patch for the current version (jackd-1.9.10) on ARM (see this forum post). Run the recipe below (copied from that post with a couple modifications).

 apt-get source jackd2
 cd jackd2-1.9.8~dfsg.4+20120529git007cdc37 
 patch -p1 -i ../jack2_armel.diff 
 dpkg-buildpackage -rfakeroot -uc -b 
 cd .. 
 sudo dpkg -i libjack-jackd2-0_1.9.8~dfsg.4+20120529git007cdc37-2ubuntu1_armhf.deb jackd2_1.9.8~dfsg.4+20120529git007cdc37-2ubuntu1_armhf.deb


Then install Rakarrack by running the following:

 sudo apt-get install rakarrack

The installation should install jackd as a dependency. To check the installed jack packages run the following:

 dpkg --get-selections | grep jack

You should see something like this:

 ubuntu@arm:~$ dpkg --get-selections | grep jack
 jack                                            deinstall
 jackd                                           install
 jackd1                                          deinstall
 jackd2                                          install
 libjack-jackd2-0:armhf                          install
 libjack0:armhf                                  deinstall
 qjackctl                                        deinstall

System Configuration

Before running anything we need to make sure that the BeagleBone is running at its maximum clock speed. To do this run the following:

 sudo cpufreq-set -f 720MHz
 sudo cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq

The output of that last command should be '720000'

  • Note: The BeagleBone needs to be running off the wall adapter to reach maximum clock rate


Next, start JACK by running the following:

 jackd -d alsa -p 256 -n 16 -S

This tells JACK that we wan to use alsa with a 16 period 256 samples/period buffer in 16-bit mode. This should be enough delay to not cause too many XRuns in JACK but not too big to be noticeable. The output should look somethings like the following:

 ubuntu@arm:~$ jackd -d alsa -p 256 -n 16 -S
 jackdmp 1.9.10
 Copyright 2001-2005 Paul Davis and others.
 Copyright 2004-2013 Grame.
 jackdmp comes with ABSOLUTELY NO WARRANTY
 This is free software, and you are welcome to redistribute it
 under certain conditions; see the file COPYING for details
 JACK server starting in realtime mode with priority 10
 creating alsa driver ... hw:0|hw:0|256|16|48000|0|0|nomon|swmeter|-|16bit
 control device hw:0
 configuring for 48000Hz, period = 256 frames (5.3 ms), buffer = 16 periods
 ALSA: final selected sample format for capture: 16bit little-endian
 ALSA: use 16 periods for capture
 ALSA: final selected sample format for playback: 16bit little-endian
 ALSA: use 16 periods for playback


Now you should be able to run the rakarrack GUI. Use `ssh -X ubuntu@192.168.0.XXX` to connect to the BeagleBone with X11 forwarding and then run `rakarrack`.

  • Note: This version of the kernel does not have a working USB gadget module so ethernet over USB does not work so the BeagleBone needs to be connected to the network.

The program should be able to find jackd by itself. If not kill the JACK processes and rerun the configuration. One way to do this is run `ps -AL | grep jack`, and then run `kill -9` with the pid number.

When Rakarrack opens, it may warn you that your CPU is not fast enough to run some of the audio effects (e.g. convolutron). Don't worry about this too much.

In Rakarrack go to 'Settings->Preferences->Audio' and lower all the downsample rates to '4000' and change all the down and up sampling types to 'Linear'. We could get a little more performance out of 'Zero Order', but this sampling does not interpolate so the quality isn't great.


With these settings we are able to run any single effect in Rakarrack without causing XRuns in JACK. Some effects can be chained together, but others are just too computationally complex.

Future Work

An interesting follow up project would be to see if another embedded Linux board (e.g. BeagleBoard xM, PandaBoard, etc.) could run Rakarrack at its default settings (or maybe its maximum settings?).