Focusrite Scarlett 2i2 working flawlessly on Ubuntu with JACK

I needed a new sound card for Ubuntu that would allow me to do some recording and playback easily. After a bit of searching and testing, I figured I would go with the Focusrite Scarlett 2i2, which is a USB sound card with 2 XLR + jack inputs, stereo monitor output and a headphone jack. It also supports +48V phantom power if you need to connect a condenser microphone.

In addition it appears to be well-tested on Linux, with several user reporting that the device just works.

Popping trouble

However, the device seemed to have some trouble with PulseAudio, which is the default audio library used in Ubuntu. Everything works, meaning that any audio application was able to output sound, and recording in Audacity gave good sound quality, but whenever I started playback or recording after switching between applications, the sound card would hang for 2 seconds and make 4 popping sounds before returning to normal operation.

The solution: JACK + PulseAudio JACK Sink

If you are going to do any serious recording in Ubuntu, or Linux in general, you should get to know JACK. It is an awesome audio library for Ubuntu that aims to make life easy for musicians, audio engineers or the occasional amateur that wants to do recordings. It runs on top of ALSA, meaning it will support almost any sound card you can think of, but does so in a way that gives you extremely low latency and doesn’t mess with sound quality. The downside? JACK doesn’t allow PulseAudio to play side-by-side with it. And every Ubuntu application tries to play through PulseAudio by default.

The solution is to install the pulseaudio-module-jack package, which will allow applications to connect to JACK, even when they have no support for JACK:

sudo apt-get install pulseaudio-module-jack

In addition, you should install a nice GUI that will allow you to control JACK easily. This is named QjackCtl:

sudo apt-get install qjackctl

After installing, just run QjackCtl from the command line or the Dash and start + connect to the JACK server.

qjackctlAfter this is done, you may check the Connect window to see if PulseAudio JACK Sink is also running, which it should do by default.

pulseaudiojacksinkThen you may open Ubuntu’s Sound Settings and set PulseAudio JACK Sink to be your Output device. From now on, all applications should work even though JACK is running.

ubuntu-soundIf you wish to, you may change QjackCtl’s settings to make JACK start whenever QjackCtl is started, and afterwards add QjackCtl to your Startup Applications in Ubuntu. This way JACK will start whenever you start your computer.

No more popping

After installing PulseAudio JACK Sink and QjackCtl, I no longer experience any popping, and the FocusRite Scarlett 2i2 works flawlessly. The sound quality is great and the latency minimal, so I would definitely recommend this sound card to any Linux user wanting to do some recording at home or on the go.

Even though I wish it would work right out of the box, installing two packages to get everything perfect is that much work, and I assume that someone figures out a good solution to merge PulseAudio and JACK in a way similar to the one I use by default sometime in the future.

Using Qt3D today

Qt3D is an amazing library for Qt that gives you the ability to render your own 3D stuff together with your existing widget or QML based GUI. The library was started by the Qt developers a few years back, but has not yet been released with the official Qt SDK. It was announced that it would be bundled with Qt5.0, but because of the state of the library at the time, its release was postponed. Even so, the library is still very mature and appears to work very well in my opinion. So I would urge you to test it out.

Simple install on Ubuntu

To use the library you have a couple of different choices. If you are running Ubuntu, you may just run the following commands:

sudo apt-get install qt3d5-dev qtdeclarative5-qt3d-plugin

And you should be good to go. Look for examples in the Qt3D documentation.

Note that Ubuntu currently doesn’t have QtQuick.Controls available, so you will have to follow the instructions below to combine Qt3D with QtQuick.Controls.

Install Qt3D into the newest Qt release

Currently Qt5.1.1 is the newest stable release of Qt and is the version I’d recommend that you use with Qt3D.

  1. Download and install Qt5.1.1.
  2. Clone Qt3D from Gitorious:
    git clone git:// qt3d
  3. Open QtCreator from your new Qt installation.
  4. Open the file from the cloned repository and configure it to use the platforms on which you want to use Qt3D (desktop, Android, etc.).
  5. Build for each platform you want to use. Set the build to Release instead of Debug mode while building. You should receive about one hundred warnings if you are building for Android. As always, ignore these.
  6. Open the build folder in a terminal and run
    make install

    This will not install to your system, but to your Qt installation, so that it gets the ability to do awesome 3D stuff.

You should now have Qt3D installed in your Qt installation and be ready to run projects that are using Qt3D.

Monitoring your unit tests without lifting a finger

I love unit testing. First of all, I think it is a good idea to test separate units of the code, but after doing so for some time, I’ve come to realize that unit tests are great for managing the software development cycle too. It all boils down to the idea that you should write tests before you write your code.

Now, this is something that I and others apparently struggle a lot with. How do you write a test for some code that doesn’t even exist yet? Even worse, how do you write a test for a piece of software that you’re not yet sure how will be used?

In computational physics, this problem arises often because we are writing code at the same time as we are trying to understand the physics, mathematics and algorithms at hand. And this is a good thing. You might want to think that one should structure all code before it is written, but this is generally a bad approach in computational physics. Especially if you’re working on something new. The reason is that you will often understand the problem and algorithms better while developing, rather than just reading about them and trying to analyze them blindly.

Keeping the tests and code healthy

But enough with the talk, let’s just assume that you are convinced that you should (or have to) implement some unit tests. At one point you are likely to be in a position where you find it tiresome to have to go into that folder where the tests are defined and run them manually. This is where Jenkins comes in to play.

Continue reading Monitoring your unit tests without lifting a finger

Setting up UnitTest++ with Qt Creator in a nice project structure

Note: I’ve found a better way to visually verify that all tests are running. Check out this post on Jenkins to see how I’m now working with my tests. The below post is still useful as a reference on how to set up UnitTest++ in Qt Creator, also when using Jenkins.

Note 2: A new and, in my opinion, better project structure is shown in this new post.

Note 3: See this post for the same project structure using the even better Catch testing framework.

When you want to make sure that your code is working properly, it is a good idea to divide it into smaller, independent pieces that may be tested individually. A unit test is a short  code that tests a smallest possible portion of your application. It is a good idea to write tests as you go and it can even be useful to write a test before you even implement the function that will be tested.

With the combination of UnitTest++ and Qt Creator, I’m now able to write unit tests while working on the code and also have some nice visual indication about failed tests during the build step of my project:


During my search for a good setup for testing my applications I realized there were a few needs that I wanted to satisfy:

  1. Creating new unit tests should be dead-easy to do. I want to spend as little time as possible on reading documentation about the testing framework.
  2. Tests should be run immediately after a new build of the source code, automatically and without the extra hassle to remember to run the tests.
  3. Tests should provide visual feedback with an easy way to get to where the tests fail. This should show up in the IDE or some other useful GUI tool.
  4. The testing framework should be fairly easy to install, especially on Ubuntu. This is because I want to be able to promote it to my fellow students.

Continue reading Setting up UnitTest++ with Qt Creator in a nice project structure

Setting up Ubuntu SDK on Kubuntu with backports enabled

Gah… So once again my temptation to install the latest and greatest causes a conflicting system setup. This time it was my attempt at installing the Ubuntu SDK on a Kubuntu system with backports enabled that conflicted. Backports are packages that are only available to newer versions of Ubuntu rebuilt for older versions, like when you want to use KDE 4.10 for Ubuntu 12.04. Although rare, when you want to install newer versions of other software you might end up with conflicts.

The result this time was the following error message upon installing the ubuntu-sdk package:

Unpacking qtchooser (from .../qtchooser_0.0.1~git20121229.g8f08405-0ubuntu1~precise1~test6_amd64.deb) ...
dpkg: error processing /var/cache/apt/archives/qtchooser_0.0.1~git20121229.g8f08405-0ubuntu1~precise1~test6_amd64.deb (--unpack):
 trying to overwrite '/usr/bin/qdbuscpp2xml', which is also in package libqt4-dev-bin 4:4.8.2+dfsg-2ubuntu1~precise1~ppa2
Processing triggers for man-db ...
Errors were encountered while processing:
E: Sub-process /usr/bin/dpkg returned an error code (1)

Trying to fix the error by removing libqt4-dev-bin only resulted in a long line of dependencies that will eventually conflict with the kde-workspace package, and you really don’t want to remove that (unless you want to get rid of KDE altogether).

To fix this, I tried a multitude of other options, only to realize that I could install all other packages in ubuntu-sdk to get what was needed to start developing apps for Ubuntu Phone and Tablet. These were installed by the single command:

sudo apt-get install qtdeclarative5-dev libqt5xmlpatterns5-dev qtscript5-dev qttools5-dev libqt5webkit5-dev qt3d5-dev qtmultimedia5-dev libqt5svg5-dev libqt5graphicaleffects5 qmlscene qtdeclarative5-dev-tools qttools5-dev-tools qtlocation5-dev qtsensors5-dev qtpim5-dev qtcreator ubuntu-qtcreator-qt5libs ubuntu-qtcreator-plugins qt-components-ubuntu qt-components-ubuntu-demos qt-components-ubuntu-examples

After this, you may launch ubuntu-qtcreator from terminal. It won’t find the Qt5 installation however, but you can point it to it by going to Tools > Options > Build & Run > Qt Versions and adding /usr/lib/x86_64-linux-gnu/qt5/bin/qmake:


Now you just need to add a new Kit pointing to the new Qt version. Before you do this, click OK and then open Options again to refresh your Qt versions available for Kits.

That’s it. Now you should be able to add a new Ubuntu UI project in Qt Creator and get started!

Getting the latest version of Ovito for Ubuntu

Ovito is a great tool to visualize atoms from molecular dynamics simulations and to perform some statistical analysis on the data. The tool is an alternative to other similar tools such as VMD and ParaView.

The main window of Ovito in the newest version.

The current version of Ovito in the Ubuntu repositories (version 0.9.2) is sadly very outdated. Even though you of course may download the latest version from Ovito’s webpages and install it locally in your home folder, I often find it better to get a newer package version.

At the Computational Physics group’s PPA I have now uploaded the latest build of Ovito for Ubuntu in a package that will automatically replace the current Ovito version. Note that this is not a release version of Ovito, but the latest version fetched from Ovito’s sources (currently nicknamed The reason is that Ovito’s creator, Alexander Stukowski, was kind enough to implement a suggestion we proposed to change the default input handler for the viewports to be the orbit input handler. This behavior feels so much more natural and makes the already great Ovito application even better.

To install the latest version of Ovito, all you need to do is to open up a terminal and type these lines:

sudo apt-add-repository ppa:comp-phys/stable
sudo apt-get install ovito

Note that the Computational Physics repository also contains newer versions of the Armadillo package, which will automatically be updated if you do not remove the repository after installing Ovito.

Set “Open containing folder” to use Dolphin and PDF files to use Okular in Firefox on Kubuntu

If you, like me, are tired of having Firefox open up Nautilus for folders and Evince for PDFs in KDE on Ubuntu, you might want to change your default application settings. To fix this once and for all, open up /usr/share/applications/defaults.list and change the line with




Then, to set up Dolphin, change




And there you are! Courtesy of Jeremy’s comment on this post.