The Linux Experiment

At home, my setup consists of three machines -  a laptop, a PC, and an XBOX 360. The latter two share a set of speakers, but I hate having to climb under the desk to switch the cables around, and wanted a better way to switch them back and forth. My good friend Tyler B suggested that I run the line out from the XBOX into the line-in on my sound card, and just let my computer handle the audio in the same way that it handles music and movies. In theory, this works great. In practice, I had one hell of a time figuring out how to force the GNOME sound manager applet into doing my bidding.

After quite a bit of googling, I found the answer on the Ubuntu forums. It turns out that the secret lies in a pulse audio module that isn’t enabled by default. Open up a terminal and use the following commands to permanently enable this behaviour. As always, make sure that you understand what’s up before running random commands that you find on the internet as root:

pactl load-module module-loopback
sudo sh -c ' echo "load-module module-loopback" >>  /etc/pulse/default.pa '

The first line instructs PulseAudio (one of the many ways that your system talks with the underlying sound hardware) to load a module called loopback, which unsurprisingly, loops incoming audio back through your outputs. This means that you can hear everything that comes into your line-in port in real time. Note that this behaviour does not extend to your microphone input by design. The second line simply tells PulseAudio to load this module whenever the system starts.

Now if you’ll excuse me, I have jerks to run over in GTA…

        

Just a heads up: This isn’t the kind of post that contains answers to your problems. It is, unfortunately, the kind of post that contains a lot of the steps that I took to fix a problem, without much information about the order in which I performed them, why I performed them, or what they did. All that I can tell you is that after doing some or all of these things in an arbitrary order, stuff seemed to work better than it did before.

It’s funny how these posts often seem to come about when trying to get hardware related things working. I distinctly remember writing one of these about getting hardware compositing working on Debian. This one is about getting reliable audio on Kubuntu 9.10.

You see, I have recently been experiencing some odd behaviour from my audio stack in Kubuntu. My machine almost always plays the startup/shutdown noises, Banshee usually provides audio by way of GStreamer, videos playing in VLC are sometimes accompanied by audio, and Flash videos almost never have working sound. Generally speaking, restarting the machine will change one or all of these items, and sometimes none. The system is usuable, but frustrating (although I might be forgiven for saying that having no audio in Flash prevents me from wasting so much time watching youtube videos when I ought to be working).

Tonight, after some time on the #kubuntu IRC channel and the #pulseaudio channel on freenode, I managed to fix all of that, and my system now supports full 5.1 surround audio, at all times, and from all applications. Cool, no? Basically, the fix was to install some PulseAudio apps:

sudo apt-get install pulseaudio pavucontrol padevchooser

Next, go to System Settings > Multimedia, and set PulseAudio as the preferred audio device in each of the categories on the left. Finally, restart the machine a couple of times. If you’re lucky, once you restart and run pavucontrol from the terminal, you’ll see a dialog box called Volume Control. Head over to the Configuration tab, and start choosing different profiles until you can hear some audio from your system. Also, I found that most of these profiles were muted by default – you can change that on the Output Devices tab. If one of the profiles works for  you, congratulations! If not, well, I guess you’re no worse off than you were before. I warned you that this was that kind of post.

Also, while attempting to fix my audio problems, I found some neat sites:

• Colin Guthrie – I spoke to this guy on IRC, and he was really helpful. He also seems to write a lot of stuff for the PulseAudio/Phonon stack in KDE. His site is a wealth of information about the stack that I really don’t understand, but makes for good reading.
• Musings on Maintaining Ubuntu – Some guy named Dan who seems to be a lead audio developer for the Ubuntu project. Also a very interesting read, and full of interesting information about audio support in Karmic.
• A Script that Profiles your Audio Setup – This bash script compiles a readout of what your machine thinks is going on with your audio hardware, and automatically hosts it on the web so that you can share it with people trying to help you out.
• A Handy Diagram of the Linux Audio Stack – This really explains a lot about what the hell is going on when an application tries to play audio in the Linux.
• What the Linux Audio Stack Seems Like – This diagram reflects my level of understanding of Linux audio. It also reminds me of XKCD.
• Ardour – The Digital Audio Workstation – In the classic tradition of running before walking, I just have to try this app out.

        

Short answer: IRC and #fedora

Long answer:

As you may recall I have been without sound for quite some time now. Finally getting sick and tired of it I ventured into the official Fedora IRC channel to try and get some help. Thankfully the people over there are very helpful. After about an hour of trying this, that and the other thing I finally found success by doing the following:

yum install pavucontrol padevchooser

This installed some very easy to use tools for PulseAudio, the component that I long thought was the cause of my problems.

PulseAudio made easy!

After pulling this up I noticed that it was sending the master audio stream to my ATi HDMI port for some reason. A quick switch of this to the “Internal Audio” and everything seemed to work fine! Not sure what caused my default audio stream to be switched to the HDMI port that I’m not even using but I’m just glad that after all of this time I have finally solved the problem!

        

Yup. Not sure why. It just happened. I have tried messing around in my audio settings and still nothing. In fact the only audio device I can get to play is not PulseAudio, or anything standard like that, but rather the Intel audio card that it found for my system. While this is all fine and promising it still doesn’t work right. When I tried to set it as my primary device and restarted my machine KDE threw a bunch of error messages my way saying that it couldn’t use the Intel device (really? because that was the only one that worked for me…) and instead fell back to PulseAudio (really? because that one doesn’t work for me…).

Why is it that Linux works great for a short while and then suddenly breaks itself?