The Useful Sound Daemon, or USound for short, is an audio I/O daemon for Unix systems, especially GNU/Linux. It provides low-latency mixing of multiple audio streams with resampling and limited format conversion, as well as audio recording. The package also includes a client library that communicates with this daemon, a libao plugin, and patches for madplay and MPlayer. USound is somewhat similar to the Enlightened Sound Daemon (EsounD), but as the name suggests, USound aims to be more useful, particularly for consumer desktop and multimedia applications. USound is free software, distributed under the GNU General Public License (GPL), except for the client library, which is in the public domain.
If you've been waiting for a better sound daemon for Unix, you can grab USound 0.2.0, which is the latest development release. This probably isn't ready for end-users yet, but I encourage other developers of applications that require audio I/O to check it out. Note that USound also requires GNU Pth.
I've decided to start posting plugins and patches for third-party applications as separate source packages, instead of including them in the USound release. For now, all I have here is a set of USound patches for Speak Freely 7.2.
I'm developing USound for Serotek Corporation, makers of FreedomBox. I'd like to thank Serotek for letting me contribute this software to the free software community.
USound uses GNU Pth to achieve portable multithreading without most of the usual headaches. Sample rate conversion is provided by the resampler from DUMB. I also got some ideas and pieces of code from Audiere. Lastly, USound uses the ring-buffer library from PortAudio. I don't know what I'd do without free software!