JACK Audio Connection Kit

{{Short description|Professional sound server for Unix-like operating systems}}

{{Infobox software

| name = JACK Audio Connection Kit

| logo = LogoJack.png

| author = Paul Davis, Stéphane Letz

| developer = JACK team

| released = {{start date|2002}}

| repo = {{URL|https://github.com/jackaudio/jack2}}

| operating_system = BSD, Linux, macOS, Solaris, Windows, iOS

| programming language = C,{{cite web |url=https://www.openhub.net/p/jack |title=JACK |work=Analysis Summary |publisher=Ohloh |access-date=2012-01-08}} C++

| genre = Sound server

| license = Server: GPL-2.0-or-later
Library: LGPL-2.1-or-later{{cite web

| url = https://jackaudio.org/api/

| title = JACK Audio Connection Kit - License

| access-date = 2021-06-08

| archive-url = https://web.archive.org/web/20210503015727/https://jackaudio.org/api/

| archive-date = 2021-05-03

| url-status = live}}

| website = {{official URL}}

| latest release version = {{multiple releases

| branch1 = JACK1:

| version1 = v0.126.0

| date1 = {{Start date and age|2022|01|15}}

| branch2 = JACK2:

| version2 = v1.9.22

| date2 = {{Start date and age|2023|02|03}}

}}

JACK Audio Connection Kit (or JACK; a recursive acronym) is a professional sound server API and pair of daemon implementations to provide real-time, low-latency connections for both audio and MIDI data between applications. JACK was developed by a community of open-source developers led by Paul Davis (who won an Open Source Award in 2004 for this work){{cite web |url=http://www.techrepublic.com/article/open-source-awards-2004-paul-davis-for-jack/ |title=Open Source Awards 2004: Paul Davis for JACK |publisher=techrepublic.com.com |access-date=24 May 2016}} 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 GPL-2.0-or-later, while the library is licensed under LGPL-2.1-or-later.

Implementations

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++ originally led by Stéphane Letz, which introduced multi-processor scalability and support for operating systems other than Linux.{{cite web|title=What's new in JACK2? - Linux Audio Conference 2009 paper by primary JACK2 author Stephane Letz|url=http://lad.linuxaudio.org/events/2009_cdm/Thursday/01_Letz/|archive-url=https://archive.today/20120709233707/http://lad.linuxaudio.org/events/2009_cdm/Thursday/01_Letz/|url-status=dead|archive-date=July 9, 2012|access-date=17 February 2010|publisher=linuxaudio.org}}

JACK can be used with ALSA, PortAudio, CoreAudio, 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. One or both implementations can run on Linux, macOS, Solaris, Windows, iOS, FreeBSD, OpenBSD and NetBSD.

The JACK API is also implemented by PipeWire for backwards compatibility as a complete drop-in replacement provider for JACK clients, mapping JACK API calls to equivalent PipeWire calls.{{cite web |title=JACK - Wiki - PipeWire/pipewire |url=https://gitlab.freedesktop.org/pipewire/pipewire/-/wikis/JACK |website=PipeWire on GitLab |access-date=11 February 2021}} If used as a replacement for ALSA and PulseAudio as well, it can unify the different sound servers and APIs that might be typically found on a machine, and allow better integration between different software. PipeWire also claims to add a number of features and fix a number of limitations compared to JACK.{{cite web |title=FAQ - Wiki - PipeWire/pipewire |url=https://gitlab.freedesktop.org/pipewire/pipewire/-/wikis/FAQ#is-pipewire-another-jack-implementation |website=PipeWire on GitLab |access-date=11 February 2021}} The use of PipeWire as the default implementation of JACK is the default on Fedora 34 and newer.{{cite web |last1=Larabel |first1=Michael |title=Fedora 34 Gets Sign-Off For Trying To Default To PipeWire For Audio Needs |url=https://www.phoronix.com/scan.php?page=news_item&px=Fedora-34-PipeWire-Attempt |website=Phoronix |publisher=Phoronix Media |access-date=11 February 2021}}

Low-latency scheduling

File:Linux kernel and daemons with exclusive access.svg, JACK daemon is an "audio daemon", i.e. it does mixing of audio from applications via software. For this it assumes to have exclusive access to the kernel's audio sub-system.]]

The scheduling requirements of JACK to achieve sufficiently low latencies were one of the driving forces behind the real-time optimization effort for the Linux kernel 2.6 series,{{cite web |url=https://lkml.org/lkml/2004/7/9/138 |title=Original announcement of a voluntary pre-emption patch for the Linux 2.6 kernel series by Ingo Molnar, 2004 |publisher=lkml.org |access-date=17 February 2010}}{{cite web |url=https://lwn.net/images/conf/rtlws11/papers/proc/p02.pdf |title=Finding Origins of Latencies Using Ftrace, paper by Steven Rostedt from the Real-time Workshop 2009 |access-date=17 February 2010}} whose initial latency performance had been disappointing compared to the older 2.4 series.{{cite web |url=http://lac.zkm.de/2006/papers/lac2006_lee_revell.pdf |title=Real-time audio vs. 2.6, Linux Audio Conference 2006 paper by Lee Revell |access-date=17 February 2010 |archive-date=10 November 2020 |archive-url=https://web.archive.org/web/20201110045534/http://lac.zkm.de/2006/papers/lac2006_lee_revell.pdf |url-status=dead }} Real-time tuning work 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.{{cite web |url=http://rt.wiki.kernel.org/ |title=Real-Time Linux Wiki |publisher=Kernel.org (The Linux Kernel Archives) |access-date=8 June 2010}}