JACK Audio Connection Kit


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 use its API. JACK has been developed by a community of open-source developers led by Paul Davis 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.

Implementations

JACK can use ALSA, PortAudio, CoreAudio, FFADO and OSS as hardware back-ends. Additionally, a dummy driver and an Audio-over-UDP driver exist. It runs on Linux, macOS, Solaris, Windows, iOS, FreeBSD, OpenBSD and NetBSD. 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, a re-implementation in C++ led by Stéphane Letz, which is under development and has introduced multi-processor scalability and support for operating systems other than Linux.

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 Linux kernel 2.6 series, whose initial latency performance had been disappointing compared to the older 2.4 series. 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.

Applications with JACK support