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LADSPA support


Note that LADSPA support is experimental currently so this page is intended mainly for developers.

A GSoC '2010 Project is using LADSPA as a backend for an EffectsUnit Project. Check it out!

Compiling with LADSPA support enabled

Required packages: ladspa-sdk

Compiling Mixxx with LADSPA support:

scons ladspa=1


If you're updating from a previous version of Mixxx, you'll need to reinstall the skins (as root):

rm -Rf /usr/local/share/mixxx/skins
scons install

(the directory can be different, e.g. /usr/share/mixxx)

Presets are now in Trunk You'll also need some presets. Just download ladspa_presets.tar.bz2 and extract the directory ladspa_presets to your Mixxx share directory (as root): <code>tar -C /usr/local/share/mixxx/ -xjf ladspa_presets.tar.bz2</code>

Required plugins

I'm not sure if Debian package names are correct.

Preset Plugin(s) Library Debian package Gentoo package Homepage
Compressor Compress caps caps-plugins
PlateReverb Plate2x2 caps caps-plugins
Delay5s delay_5s or cmt ladspa-cmt
DJFlanger djFlanger swh-plugins swh-plugins
Karaoke karaoke swh-plugins swh-plugins


The LADSPA window is hidden by default. You can enable it by activating LADSPA > Show LADSPA window from the menu.

Currently the following skins are supported: outlineSmall, outline, outlineClose, traditional, hercules, nCut, Collusion (1280), Collusion (1280-WS).


All the LADSPA code is already in trunk, it just needs to be enabled by default. In order for us to do this “right”, here's the stuff that needs to be done:

  • Make LADSPA pane use QGridLayout (?)
  • Pick the default LADSPA plugins:
  • Make sure we have preset XML files for all of these.
  • Build them on OS X, recommend them on Linux, repack Audacity plugin build on Windows or have installer fetch them from Audacity's site.
  • Use pre-built plugins for Win32 (Audacity win32 LADSPA Plugins) and Linux (cmt, caps, swh-plugins).
  • Add LADSPA presets and plugins to trunk
  • Modify SConscript to install them on OS X, Linux (and move to dist dir on Win32)
  • Modify mixxx.nsi to install/uninstall them on Windows
  • Update src/debian/rules file (might not need editing, but doublecheck)
    • Figure out deployment strategy for Linux:
      • On Windows/OS X, we'll just bundle them
      • … but on Linux, we may only want to ship the presets files and require users to install their distro's LADSPA plugins package (Anyone have ideas here?)
  • the pane with the slots should have a scrollbar (ie. put it in a QScrollArea or whatever it's called). The 3 slots don't currently show up right on all OSes, so putting it in a scoll area will fix this plus maybe let us make more slots or something later.
  • the little “x” to remove an effect from a slot needs to be right-aligned, instead of just pasted where-ever.
  • someone should re-evaluate how the effects are layed out inside each slot, because all of that code was done before Qt 4 (and before QLayouts existed). We don't have to change it, but I think the “x” button is probably just hardcoded to be in some position. Would be good to know what work will be need to be done later.
  • Fix the text getting cut off. Some of the QLabels in the slots get cut off. Needs to word wrap or something smart.
  • Fix the duplicate wet/dry knobs for some plugins.
  • and/or either remove our non-working wet/dry knob or make it work. :)
  • The delay time knob in the delay plugin is hard to use because it's not tempo synced. There is a reasonable solution to this, which is to add some sort of “tempo synced control” declaration in the LADSPA xml format, and gives a conversion ratio from BPM to whatever the knob is in (millisec probably). Then our LADSPA code would see this, and make the knob increment/decrements dependent on the detected BPM of whatever's playing.

At the very least, all the GUI problems and knobs-not-working need to be resolved before LADSPA is ready.


LADSPA: How is it loaded into Mixxx?

LADSPA: How does Mixxx activate and process a LADSPA effect?

LADSPA Classes


  • Has all the LADSPAInstances, configurations, knobs, connections, everything.
  • Will update the value for every control port (ControlObject → LADSPAControl)
  • Will process the samples.


  • Handles display/ui, instantiates LADSPAPresetManager.


  • Will load all plugins available (uses LADSPALibrary)
  • Returns LADSPAPlugins by slot # or label.


  • Given a file, load every plugin this file has.
  • LADSPA plugins may be bundled inside one library (small variations of each other, usually)


  • Holds the descriptor, has few operations to interface with the descriptor.
  • Has the instantiate method, to create a LADSPAInstance.



  • Has the process method to process samples.
  • Has the connect method to bind the ports of the plugins to LADSPAControl variables.
  • Creates ConfigKeys and ControlObjects for Enable/Disable and for the Wet&Dry.
  • LADSPAInstanceStereo/Mono: If a Plugin is Mono, Mixxx makes 2 instances to process Right/Left signals separetely.


  • Holds a pointer to a LADSPA_Data.
  • Has operation to get a value and put into the buffer for LADSPA_Data smoothly.


  • Load XML into LADSPAPresets, instantiates LADSPALoader. An example of a LADSPA preset xml for DJFlanger:
 <Plugin ID="0">djFlanger</Plugin>
  <Label>LFO sync</Label>
  <Label>LFO period</Label>
  <Label>LFO depth</Label>


  • Has the port names, knobs much like LADSPAPlugin.
  • Has the instantiate method that will
  • LADSPAPlugin::instantiate() → LADSPAInstance
  • LADSPAPreset::instantiate() → LADSPAPresetInstance


  • Instantiates the LADSPAPlugin into LADSPAInstance
  • Run the connect method for every control port
  • Adds everything to the EngineLADSPA


  • Part of the UI, is where you drag the plugins to.
Translations of this page:
ladspa.1331345611.txt.gz · Last modified: 2012/03/09 21:13 by rryan