JACK Audio Connection Kit
 | |
| Original author(s) | Paul Davis, Stéphane Letz |
|---|---|
| Developer(s) | JACK team[1] |
| Stable release | 1.9.6
/ 18 October 2010 |
| Repository | |
| Written in | C[2], C++ |
| Operating system | Linux, FreeBSD, Mac OS X, Windows, Solaris |
| Type | Sound server |
| License | GNU GPL, GNU LGPL |
| Website | jackaudio.org |
JACK (a recursive acronym which expands to JACK Audio Connection Kit) is a professional sound server daemon that provides real-time, low latency connections for both audio and MIDI data between applications that implement its API. It is under constant development by a community of open source developers led by Paul Davis (who won an Open Source Award in 2004 for this work[3]) and has been a key piece of infrastructure and the de-facto standard for professional audio software on Linux since its inception in 2002. The server is free software, licensed under the GNU GPL, while the library is licensed under the more permissive GNU LGPL.
Design paradigms
The design focuses on two key areas: synchronous execution of all clients, and low latency operation.[4] To support JACK, an application has to register a process() callback that deals with incoming audio and computes audio for its output(s). It is not invoked by the application itself, but rather by the JACK daemon, which serves as a central instance in the audio signal graph. For simplicity and efficiency, JACK mandates the use of 32-bit float audio data, and a common (but user-configurable) sample rate.
JACK has brought the UNIX philosophy of small, specialized tools ("do one thing, and do it well") to real-time audio, which lends itself well to the open source programming methodology, as it fosters code re-use and creative flexibility. The JACK API is easier to implement than native hardware access and allows for cross-platform operation. These advantages have been powerful incentives to developers and have led to JACK's widespread success and rapid adoption in the free audio software community.
Implementations
JACK can use ALSA, PortAudio, CoreAudio, FreeBoB, FFADO and OSS as hardware back-ends. Additionally, a dummy driver (useful if no sound output is desired, e.g. for offline rendering) and an Audio-over-UDP driver exist. It runs on Linux, Mac OS X, Solaris, Windows, and FreeBSD. The JACK API is standardized by consensus, and two compatible implementations exist: jack1, which is implemented in plain C and has been in maintenance mode for a while, and jack2 (originally jackdmp), a re-implementation in C++ led by Stéphane Letz, which is under aggressive development and has introduced multi-processor scalability and support for operating systems other than Linux.[5]
Low latency scheduling
The scheduling requirements of JACK to achieve sufficiently low latencies have been one of the driving forces behind the real-time optimization effort for the current Linux 2.6 kernel series,[6][7] whose initial latency performance had been disappointing compared to the older 2.4 series.[8] Real-time tuning work has culminated in numerous scheduling improvements to the mainline kernel and the creation of an -rt branch for more intrusive optimizations in the release 2.6.24, and later the CONFIG_PREEMPT_RT patch.[9]
Applications with JACK support
See Category:Audio software with JACK support.
See also
References
- ^ "JACK Developer Information". jackaudio.org. Retrieved 2 January 2010.
- ^ "Ohloh Analysis Summary - JACK". Ohloh. Retrieved 2 January 2010.
- ^ "Open Source Awards 2004: Paul Davis for JACK". techrepublic.com.com. Retrieved 16 February 2010.
- ^ "JACK Connecting a world of audio". jackaudio.org. Retrieved 15 February 2010.
- ^ "What's new in JACK2? - Linux Audio Conference 2009 paper by primary JACK2 author Stephane Letz". linuxaudio.org. Retrieved 17 February 2010.
- ^ "Original annoucement of a voluntary pre-emption patch for the Linux 2.6 kernel series by Ingo Molnar, 2004". lkml.org. Retrieved 17 February 2010.
- ^ "Finding Origins of Latencies Using Ftrace, paper by Steven Rostedt from the Real-time Workshop 2009" (PDF). Retrieved 17 February 2010.
- ^ "Real-time audio vs. 2.6, Linux Audio Conference 2006 paper by Lee Revell" (PDF). Retrieved 17 February 2010.
- ^ "Real-Time Linux Wiki". Linux Kernel Organization. Retrieved 8 June 2010.