Southend Linux User Group

Jack

Jack an Audio Mixer for your Desktop

jackapp

Introduction

From time to time you may need more than one audio application running simultaneously, the trouble is ALSA doesn’t support multiple devices using the audio driver at the same time and even if it did for an audio technician this is not entirely what they need. Enter an application called Jack it stacks itself between your audio hardware driver and audio applications installed with a suitable jack plugin. On it’s own Jack does nothing you need other applications that highlight it’s function. Consider “Jack Connection Kit” as a background server and applications such as:

  • Hydrogen
  • Muse
  • ReZound
  • Ardour
  • Audacity
  • Jamin
  • Rosegarden
  • Audacious
  • Pure Data
  • Super Collider

These to name but a few are all examples client applications that can use Jack Server. The question is how, I have personally searched the internet for someone who could answer my questions on how to use Jack and could find none, as it turns out Gary (Tailzer) a regular contributor to this Linux wiki site gave me some of the answers I needed to have some understanding on how Jack server and it’s client applications function together we hope you find them useful.

Assumptions

We assume your audio hardware is functioning and that jack is installed and running

Testing Jack

This is not as hard as you might imagine, with jack started it should look something like the example above find an audio application that uses a Jack Plugin connector Audacious will do for a start. If this is not already installed we recommend you install it, as an audio player it is a close facsimile of the old Xmms player which seems to have been dropped from further development. A jack plugin is available for Audacious but this needs to be selected.

audacious.preview

You need to use your right hand mouse button on “Audacious” a bit to locate it’s preferences we found them on the top left hand corner just above the display.

Select Audio >> Current output plugin: Jack Output Plugin 0.17

Lets go back to the Jack audio connector for a moment and confirm a few aspects of the preferences in setup. Click with your mouse on the Setup check your settings with the one displayed below they need not be exactly the same but it will give you a base line for your own settings.

jack01

jack02

jack03

jack04

Play a selected tune and if you can hear the audio you have a pretty good indication that jack it is working.

Now to familiarise yourself with other options available in jack Messages is self explanatory but is still a very useful tool to have at ones disposal. Status offers a glimpse of the current settings as determined by preferences in Jack Control.

The remaining two options are very similar in operation we will concentrate on Connect as perhaps this is the easiest of the two to understand, lets first look at this option with no additional applications installed. To accomplish this exit from “Audacious” if this is still open, you should now if you click on “Connect” option it should look like the example below if not you need to find out what application you have running and exit from it.

jack05

Now lets run Audacious again without a song running you will see exactly the same output even when refresh button is pressed. However run a song, any mp3 file will do and expand the option by clicking the ”'”+””’ sign you should see a display similar to that below.

jack06

This in itself shows little, however even from this simple diagram one can transform the connection displayed, swapping for example left to right and right to left.

Select out_0 and playback_1 then click disconnect repeat this sequence for out_1 and playback_2 you can then swap the outputs.

jack07

jack08

jack09

jack10

jack11

This is but a small component of what can be achieved, in the next step we will add to our applications and incorporate some additional functionality using ”'”Jamin””’ an application we can set between “Audacious” and jack.

jack12

jack13

jack16

jack14

jack15

Jamin again on it’s own will do absolutely nothing it only works when other program applications are attached to it. At first sight it is very confusing but to put you straight the input is on the left and the output is on the right. There are some 20 possible scene alterations “Jamin”call’s scenes at the top that you can switch between, the middle has a variety of selectable wave shapers equalisers and peak meters and if that was not enough you have some filter that alter gain and threshold options on the bottom.

Jamin is all about manipulating frequencies and amplitude both on the input and the output these settings can alter the tone and quality of the music processed through it. If the amplitude is to low for example this can boosted if the amplitude is to high these can be normalised to acceptable levels. As you change to a new scene any alteration is memorised so that when you return to this scene all settings are restored to those you last left them. Most of the time your scenes are in Red by setting them these change to Green you can then alter the settings under each scene and the settings will be remembered. You can set a new scene by right clicking on the scene button and clicking set, in addition you can name the scenes in a similar manner.

Author: Alan Campion - Page reference: 2928
Last modified: Alan Campion - 2015-01-22