A sound server is

software Software consists of computer programs that instruct the Execution (computing), execution of a computer. Software also includes design documents and specifications. The history of software is closely tied to the development of digital comput ...

that manages the use of and access to

audio Audio most commonly refers to sound, as it is transmitted in signal form. It may also refer to: Sound *Audio signal, an electrical representation of sound *Audio frequency, a frequency in the audio spectrum *Digital audio, representation of sound ...

devices (usually a

sound card A sound card (also known as an audio card) is an internal expansion card that provides input and output of audio signals to and from a computer under the control of computer programs. The term ''sound card'' is also applied to external audio ...

). It commonly runs as a

background process A background process is a computer process that runs ''behind the scenes'' (i.e., in the background) and without user intervention. Typical tasks for these processes include logging, system monitoring, scheduling, and user notification. On a Wind ...

Sound server in an operating system

In a

Unix-like A Unix-like (sometimes referred to as UN*X, *nix or *NIX) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Uni ...

operating system, a sound server mixes different data streams (usually raw

PCM audio Pulse-code modulation (PCM) is a method used to digitally represent analog signals. It is the standard form of digital audio in computers, compact discs, digital telephony and other digital audio applications. In a PCM stream, the amplitude o ...

) 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

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 The arts or creative arts are a vast range of human practices involving creativity, creative expression, storytelling, and cultural participation. The arts encompass diverse and plural modes of thought, deeds, and existence in an extensive ...

, ESD, JACK,

PulseAudio PulseAudio is a network-capable sound server program distributed via the freedesktop.org project. It runs mainly on Linux, including Windows Subsystem for Linux on Microsoft Windows and Termux on Android; various BSD distributions such as ...

) * Sound subsystem (described as kernel modules or drivers; e.g.

OSS OSS or Oss may refer to: Places * Oss, a city and municipality in the Netherlands * Osh Airport, IATA code OSS People with the name * Oss (surname), a surname Arts and entertainment * ''O.S.S.'' (film), a 1946 World War II spy film about ...

, ALSA) * Operating system kernel (e.g.

Linux Linux ( ) is a family of open source Unix-like operating systems based on the Linux kernel, an kernel (operating system), operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically package manager, pac ...

Unix Unix (, ; trademarked as UNIX) is a family of multitasking, multi-user computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, a ...

)

Motivation

Sound servers appeared in Unix-like operating systems after limitations in

Open Sound System The Open Sound System (OSS) is an interface for making and capturing sound in Unix and Unix-like operating systems. It is based on standard Unix devices system calls (i.e. POSIX read, write, ioctl, etc.). The term also sometimes refers to ...

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 A demon is a malevolent supernatural being, evil spirit or fiend in religion, occultism, literature, fiction, mythology and folklore. Demon, daemon or dæmon may also refer to: Entertainment Fictional entities * Daemon (G.I. Joe), a character ...

. 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

{{As of , 2012 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

* Enlightened Sound Daemon * JACK * Network Audio System *

PipeWire PipeWire is a low-level server and multimedia framework for handling audio and video streams on Linux. Created by Wim Taymans at Red Hat, it aims to unify audio and video processing by providing low-latency capture and playback functionality. Pi ...

* sndio -

OpenBSD OpenBSD is a security-focused operating system, security-focused, free software, Unix-like operating system based on the Berkeley Software Distribution (BSD). Theo de Raadt created OpenBSD in 1995 by fork (software development), forking NetBSD ...

audio and MIDI framework

Streaming

Icecast Icecast is a streaming media project released as free software maintained by the Xiph.Org Foundation. It also refers specifically to the Server (computing), server program which is part of the project. Icecast was created in December 1998/Janua ...

* SHOUTcast

References

External links

Introduction to Linux Audio

Servers (computing)