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The idea is to make PulseAudio the default sound system on Ubuntu, replacing the Esound Sound Daemon (esd) and ALSA dmix. PulseAudio is a drop-in replacement for Esound, but adds new features, opening it for many entirely new areas.


Apple managed to standardize on a single powerful sound system (CoreAudio) for MacOSX which makes almost all users happy, ranging from normal day-to-day desktop users to gamers, to professional audio people. We should be able to provide the same on Linux. PulseAudio can currently provide the functionality at least partially, with the only notable exception being pro audio. PulseAudio is a modular sound server, kind of an "application server" for audio. Beyond the obvious sound mixing functionality it offers advanced audio features like "desktop bling", hot-plug support, transparent network audio, hot moving of playback streams between audio devices, separate volume adjustments for all playback or record streams, very low latency, very precise latency estimation (even over the network), a modern zero-copy memory management, a wide range of extension modules, availability for many operating systems, and compatibility with 90% of all currently available audio applications for Linux in one way or another.

In the future it is expected that PulseAudio will extend to professional audio stuff, entering JACK's current application area. This however is not relevant for the implementation of this spec, at least at this time.

Use cases


This specification changes the default sound daemon for Ubuntu. The same is immediately applicable to Xubuntu, if desired.


Mode of operation

In order to provide the highest possible audio quality, use all features like hal support and dynamic stream handling, and not opening any potential attack vector, the upstream recommended mode of operation is to have a permanent pulse daemon running as the user, without automatic module unloading. The current version automatically releases the sound card if it is not used, and has hal/ConsoleKit integration, so that multiuser support works.

As long as nobody is using the sound card, OSS legacy apps continue to work.


PulseAudio emulates the OSS, ALSA, and esound API (amongst others), so that existing applications can be moved to Pulse without much effort. Just for the record, this emulation has nothing to do with ALSA's OSS emulation, Pulse will work even if these modules are loaded (but not used).

For fully transparent OSS emulation, we should check whether the FUSD userspace devices implementation is mature enough to replace the current LD_PRELOAD hacks.


PulseAudio offers three different graphical user interfaces for controlling audio (see a screenshot:

  1. pulseaudio volume control: Controls the volume of sinks, sources, and streams, and allows the user to move streams between sinks.
  2. pulseaudio preferences: configure network related services including multicast
  3. panel applet: notify about changes of sound hardware, choose default device, call the other pulseaudio tools.

The volume control and preferences applications are sufficient for all the use cases mentioned above. The panel applet is just "nice to have" for control freaks, so we should ship it, but not activate by default.

We will ship the pulseaudio volume control by default, since it is a very convenient interface to control the volume per stream. However, we will keep the default Gnome mixer applet (which controls the hardware mixer levels) for now.



Data preservation and migration

Upgrades will be handled through ubuntu-desktop introducing a dependency to pulseaudio-esound-compat, which C/R/P: esound.



DesktopTeam/Specs/CleanupAudioJumble (last edited 2008-08-06 16:22:41 by localhost)