#nocomments y

In recent versions PulseAudio integrates the numerous mixer elements ALSA exposes into one single powerful slider which tries to make the best of the granularity and range of the hardware and extends that in software so that we can provide an equally powerful slider on all systems. That means if your hardware only supports a limited volume range (many integrated USB speakers for example cannot be completely muted with the hardware volume slider), limited granularity (some hardware sliders only have 8 steps or so), or no per-channel volumes (many sound cards have a single slider that covers all channels), then PulseAudio tries its best to make use of the next hardware volume slider in the pipeline to compensate for that, and so on, finally falling back to software for everything that cannot be done in hardware. This is explained in more detail here.

Now this algorithm depends on that we know the actual attenuation factors (factors like that are usually written in units of dB which is why I will call this the "dB data" from now on) of the hardware volume controls. Thankfully ALSA includes that information in its driver interfaces. However for some hardware this data is not reliable. For example, one of my own cards (a Terratec Aureon 5.1 MkII USB) contains invalid dB data in its USB descriptor and ALSA passes that on to PulseAudio. The effect of that is that the PulseAudio volume control behaves very weirdly for this card, in a way that the volume "jumps" and changes in unexpected ways (or doesn't change at all in some ranges!) when you slowly move the slider, or that the volume is completely muted over large ranges of the slider where it should not be. Also this breaks the flat volume logic in PulseAudo, to the result that playing one stream (let's say a music stream) and then adding a second one (let's say an event sound) might incorrectly attenuate the first one (i.e. whenever you play an event sound the music changes in volume).

Incorrect dB data is not a new problem. However PulseAudio is the first application that actually depends on the correctness of this data. Previously the dB info was shown as auxiliary information in some volume controls, and only noticed and understood by very few, technical people. It was not used for further calculations.

Now, the reasons I am writing this blog posting are firstly to inform you about this type of bug and the results it has on the logic PulseAudio implements, and secondly (and more importantly) to point you to this little Wiki page I wrote that explains how to verify if this is indeed a problem on your card (in case you are experiencing any of the symptoms mentioned above) and secondly what to do to improve the situation, and how to get correct dB data that can be included as quirk in your driver.

Thank you for your attention.

While tracking down some surround sound related bugs I was missing a speaker setup and testing utility. So I decided to do something about it and I present you gnome-speaker-setup:

The tool should be very robust and even deal with the weirdest channel mappings. OTOH the artwork is not really good and appropriate. But I hope it still shows some resemblance to other UIs of this type. If you are an artist wand want to contribute better artwork make sure to go through the Gnome Art Requests page, and more specifically this particular request.

This (or something like it) will hopefully and eventually end up in some way or another in gnome-media. Until that day comes I'll maintain this tool independently.

To compile this you need a recent Vala and libcanberra 0.23.

It's easy to get lost in /sys and not much fun typing long udevadm info command lines all the time. Today, when I had enough of that I sat down and spent an hour to write a little UI for exploring the udev/sysfs tree: udev-browse. I wrote it for my own use, but I am quite sure I am not the only one who wants a little bit simpler access to the device tree. So here you go.

And since everybody loves screenshots here you go:

Two usability hints: if you run udev-browse from a directory in /sys udev-browse will automatically present the device of that path on startup. And if you know the name of a device you can just type it into the device listbox (which is focussed by default). The usual Gtk+ live search will then find you the right entry right-away. It's pretty nifty.

It's written in Vala with minimal dependencies.

I want to keep the maintainership burden for this minimal. So no tarballs, no releases, and I won't reply to your emails regarding this tool, unless they include a good, clean, git formatted patch. Thank you for your understanding.

Anyone wants to package this for Fedora? I'd be very thankful if someone would pick it up.

Have fun.

Everyone and his dog seem to call libxml2's xmlCleanupParser() at inappropriate places. For example Empathy does it, and Abiword does it too. Google Code Search seems to reveal at least Inkscape and Dia do it as well.

So, please, if your project links against libxml2 verify that it calls xmlCleanupParser() only once, and right before exiting! And if it calls it more often or somewhere else, then please fix that!

For more information see my post on fedora-devel.

Thanks for your time.

Building on what Havoc wrote two years ago about the fallacies of OOM safety (Out Of Memory) in user code I'd like to point you to this little mail I just posted to jack-devel which tries to give you the bigger picture. Should be interesting for non-audio folks, too.

Say NO to OOM safety!

Folks! Since quite some time now the kernel exports the DMI machine information below /sys/class/dmi/id/. You may stop now parsing the output of dmidecode thus depending on external tools and privileged code.

For example, to read your BIOS vendor string all you need to do is this:

$ read bv < /sys/class/dmi/id/bios_vendor
$ echo $bv

Which is of course much simpler, and cleaner, and safer than anything involving dmidecode.

Thank you for your time!

#nocomments yes

<rant>

So in the past Ubuntu packaged PA in a way that, let's say, was not exactly optimal. I thought they'd gotten around fixing things since then. Turns out they didn't. Seems in their upcoming release they again did some genius thing to make PA on Ubuntu perform worse than it could. The Ubuntu kernel contains all kind of closed-source and other crap to no limits, but backporting a tiny patch that is blessed and merged upstream and in Fedora for ages, that they won't do. Gah.

And it doesn't stop there. This patch is an outright insult. This is disappointing.

Madness. Not good, Ubuntu, really not good! And I'll get all the complaints for this f**up again. Thanks!

/me is disappointed. Ubuntu, you really can do better than this.

</rant>

#nocomments y

Kinda fun watching this video. As it seems the big new features of the Windows 7 audio stack are the ability to move streams while they are live, to do role-based policy routing, and to pause streams during phone calls. Hah! That's so yesterday! A certain sound server I happen to know very well has been supporting this for a longer time already, and you can even buy that logic in various consumer products.

Nice to know that in some areas of the audio stack it's not us who need to play catch-up with them, but they are the ones who need to play catch-up with us.

CIO has an interview with me.

LWN covers Paul's and my talk at the Audio MC at LPC, Portland. (Subscribers only for now)

Update: Here's a free subscriber link.