Jack2 Audio Connection Kit

Jack2 is the connector for audio within and between computers.  It connects your audio soundcard to the guts of your computer using a simple to visualize jackfield, where you connect audio paths from one output to any number of inputs.  You can also connect several computers’ audio together over ethernet!  It is available for Linux (Ubuntu Studio), MacOS, and Windows!  It does not know multi-channel audio natively, so you have to hook up the left and the right ‘cables’ independently.

My first exposure to Jack was back in Ubuntu 10.04 where I installed it manually in a system that had ALSA (Advanced Linux Sound Architecture) and an early version of Pulseaudio  installed.  It drove me crazy, no audio or audio that had dropouts.  Dozens of settings poorly documented.  AARRRRGH!

9/2019  Update:    Ubuntu 18.04 runs jacks quite nicely without problem when set up by KXStudio   (See Article)

No longer! Ubuntu Studio comes with Jack2 already installed so all that grief is mostly behind you.  Many web sources tell you to get rid of Pulseaudio, but the case is not so compelling as it once was, but if low latency or several sound cards are in your plan, dump it.  Check out my article “Use Pulseaudio with Jack Audio Connection Kit?”

You should have your final soundcard(s) installed when you install Ubuntu-Studio so that it can pick up the cards automatically.  Jack comes with a little utility called qjackctl that lets you set all the necessary configuration that lets you correct much of what might not work right away.  KXStudio cadence application (See below) is much prettier, and shows status in a much more easy to understand way and hooks up plugins and other features that I didn’t figure out Cadence’s tools are more robust than qjackctl, although it has no internal provision for saving patches in a patchbay.   No audio can usually be fixed with a command line utility called alsamixer because some sound card drivers set the volume to “0” not “11”.

There are packages from a site called KXStudio that make using Jack2 on Linux beautiful.  If you dive into KXStudio, you will not need  most of the Jack2 utilities like Patchage, qjackctl, etc.  I will have a script on this site soon that automates installing all these Uber Cool features.

Once you can hook up an audio editor like Audacity to the audio outputs and connect a parametric equalizer to the microphone inputs and the equalizer to Audacity inputs, along a  Jack meterbridge or spectrum analyzer you can see the power of this system. Jack can hook up Lapsda and .vst plugins for a multitude of effects.

NetJack is a way to hook up several computers’ audio  together via ethernet with one master computer connecting to another, or several others.  This can work over a typical quiet office network, but the NetJack audio should be on its own network with no competing uses of the bandwidth.  If there is too much audio flying around even a 1 GB network can get overloaded.

There are more convenient and higher fidelity options than NetJack, Such as Zita-NJBridge  the included zita-j2n and zita-n2j open audio ports to other jack instances on other networked computers.

So, the possibility of shipping audio around between workstations and a server is pretty easy, getting rid of lots of conventional cabling, and removing hundreds or thousands of places where the audio can get degraded.

One of the trickiest parts of Jack2 is making persistent setups and patchbay configurations that can automatically re-appear upon reboot or relogin, and understanding the relationships between applications started by different users and different sessions.  There is no standard command line tags for jack naming, and automatic jack connecting.  Auto-connecting a program’s output generally takes the form of

-<port tag>  Jack_Device_name:Jack_port_name

On some programs the Jack_Port_Name can be a regex, sometimes a complete name, or sometimes a port name less the variable part.  You have to play with the program to figure it out.