A sound server is software that manages the use of and access to audio devices (usually a sound card). It commonly runs as a background process. Sound server in an operating system In a Unix-like operating system, a sound server mixes different data streams and sends out a single unified audio to an output device. The mixing is usually done by software, or by hardware if there is a supported sound card. Layers The "sound stack" can be visualized as follows, with programs in the upper layers calling elements in the lower layers: Applications (e.g. mp3 player, web video) Sound server (e.g. aRts, ESD, JACK, PulseAudio) Sound subsystem (described as kernel modules or drivers; e.g. OSS, ALSA) Operating system kernel (e.g. Linux, Unix) Motivation Sound servers appeared in Unix-like operating systems after limitations in Open Sound System were recognized. OSS is a basic sound interface that was incapable of playing multiple streams simultaneously, dealing with multiple sound cards, or streaming sound over the network. A sound server can provide these features by running as a daemon. It receives calls from different programs and sound flows, mixes the streams, and sends raw audio out to the audio device. With a sound server, users can also configure global and per-application sound preferences. Diversification and problems there are multiple sound servers; some focus on providing very low latency, while others concentrate on features suitable for general desktop systems. While diversification allows a user to choose just the features that are important to a particular application, it also forces developers to accommodate these options by necessitating code that is compatible with the various sound servers available. Consequently, this variety has resulted in a desire for a standard API to unify efforts. List of sound servers aRts Enlightened Sound Daemon JACK Network Audio System PipeWire PulseAudio sndio - OpenBSD audio and MIDI framework Streaming Icecast SHOUTcast References External links Introduction to Linux Audio RFC: GNOME 2.0 Multimedia strategy Servers (computing)