Have you ever wanted to take the audio output of one piece of software and send it to another? How about taking the output of that same program and send it to two others, then record the result in the first program? Or maybe you're a programmer who writes real-time audio and music applications and who is looking for a cross-platform API that enables not only device sharing but also inter-application audio routing, and is incredibly easy to learn and use? If so, JACK may be what you've been looking for.
JACK is system for handling real-time, low latency audio (and MIDI). It runs on GNU/Linux, Solaris, FreeBSD, OS X and Windows (and can be ported to other POSIX-conformant platforms). It can connect a number of different applications to an audio device, as well as allowing them to share audio between themselves. Its clients can run in their own processes (ie. as normal applications), or can they can run within the JACK server (ie. as a "plugin"). JACK also has support for distributing audio processing across a network, both fast & reliable LANs as well as slower, less reliable WANs.
JACK was designed from the ground up for professional audio work, and its design focuses on two key areas: synchronous execution of all clients, and low latency operation. More background information is available.
Understanding JACK in different ways
The term "JACK" doesn't really identify anything very precisely. What "JACK" means depends a little bit on your perspective. There are several ways of understanding the term, all equally valid:
- The JACK API
- The definition of the data structures, protocols and functions used by programs that use JACK
- An implementation of the API
- Actual software, including a server application, often called "jack", and a library used by clients. There are already two implementations of the API, known as "jack1" and "jack2" (formerly "jackmp"). Different implementations are (in almost every way) drop-in replacements for each other.
- A GUI control application
- The existing implementations do not come with any GUI at all. To make life easier for most users, GUI control apps exist that allow easy modification of JACK startup parameters, and ways to monitor the state of a running JACK system.
qjackctlis the most widely used GUI control application.
- A running instance of JACK with a variety of JACK-aware applications
- This will likely include the server application, the control GUI, and zero or more actual applications that use JACK, such as Ardour (a DAW), Hydrogen (a drum machine) or many, many more.
JACK has been released on iOS thanks to the hard work of Christian Schoenebeck at crudebyte for the GUI control application and server, and GRAME on the server part. The server code is embedded in a control application that will launch the server, allow to adjust settings, and manage connections between applications. The application is free and can be downloaded here.
Our web hosting service changed something on their servers that broke the Trac section of the website (trac.jackaudio.org). Work is in progress to migrate the content to github and provide forward links. If you are still reading this article, that work is not yet complete.
Jack 1.9.9 is API compatible with latest Jack 0.121.3 version.
What is new:
- Adrian Knoth fix in midiseq.c.
- Fix library symbols export issue.
- Cleanup drivers and internals loading code.
- jackctl_driver_params_parse API moved in public control.h.
- More general drivers/internals loading model on Windows.
- Factorize code the server/client request in JackRequestDecoder class.
- More robust server/client protocol. Implement shutdown for in server clients.
- Better time-out management in NetJack2.
- Experimental system port alias use in Windows JackRouter.
As of April 2012 there seems to be driver problem that affects the audio interface on the Macbook when it is used in 24 or 32 bit mode. To avoid the resulting distortion, use the -S flag to the ALSA backend to force it to use 16 bit sample data format.
Jack 1.9.8 is API compatible with latest Jack 0.121.3 version.
This is the first version that contains the new MIDI driver model developed by Devin Anderson in spring of this year. This includes the Linux FFADO driver, the Mac OSX CoreMIDI driver, the Windows WinMME driver, and a new Linux 'alsarawmidi' slave driver that can run alongside other master drivers (i.e. FFADO).
JACK 0.121.3 is a bug fix release containing (almost) no new functionality. It is required if you want to use JACK1 on OS X with any clients that use weak linkage for JACK feature detection (e.g. Ardour).
As on other platforms, JACK on Windows is a multi-purpose application that connects audio and MIDI using the Windows system drivers... It connects (OUTPUT) to those audio drivers using the PortAudio project (so Jack can connect using dsound, wmme, WDMKS, ASIO, WASAPI, and WaveRT) depending on what the soundcard's drivers support. Currently Jack for Windows only supports 32-bit applications, but a new version is currently being tested that supports both 32-bit and 64-bit audio applications.
JACK 0.121.2 has been released. This correctly includes changes made to jackd.py's device reservation handling. They were done before 0.121.0 was released but not included in that version. No functional changes to regular JACK functionality are present in this upgrade.