Professional A/B Crossfader Mixing in Ardour with Mixxx


Stereo DJ X-fade LV2 plugin in Ardour3

After finding out that my cheap turntables suffer from a massive amount of wow and flutter I have had to abandon mixing vinyl entirely until I get a pair of “Super OEM” DJ turntables. These are the Hanpin based Original equipment manufacturer (OEM) turntables that many manufacturers have taken up for their own products. Like this DJ Tech SL-1300MK6 Turntable



Ain’t she beautiful ?

But until then I decided to go entirely over to digital mixing. I want to be able to play as live as possible but also be able to record in Ardour as much of the mix as I can. This is essentially an identical process to recording an acoustic session in a studio to a multi-track recording. However here we are recording the tracks, with crossfades that can be edited later, as well as all the samples and effects. I became frustrated with Mixxx’s implementation of mixing using Jack. This is still in development. For example only a master output contains cross-faded mixes. The crossfader does not change the volume of the separate Jack outputs for each deck, as it probably should do if you think about it. I started examining Jack Audio Connection Kit and Ardour. The entire point of Jack is to solve these kind of studio setup problems. Then I had a HUGE revelation ! Too many people seem to think of Ardour and even Jack Audio Connection Kit as a kind of glorified sound card output routing mechanism. They could probably be forgiven for this if they have not made practical use of Jack. This is not something that can be explained unless you have really worked with Linux audio. The entire system is one HUGE mixer and the Linux audio world has made huge breakthroughs in this area that are really revolutionary when it comes to digital audio mixing and studio work.

Ardour is really no different to a DJ mixer. There seems to be a number of myths and misconceptions that separate “DJ Mixing” from “Studio Mixing” like Ardour. They are really based on all the same principles. For example look at this Pioneer DJM-850 mixer …



Notice the A/Thru/B buttons. These determine which channels the Crossfader controls. A/B mixing should be familiar to any Studio Engineer and is the same concept that is used in vision mixing. What we can’t see is the “Bus” that’s under the front panel that routes the audio depending on the A/B settings. I managed to get an initial setup of this working in Ardour.

Linux Magazine called Ardour a “Super Mixer” in its June 2013 issue, so I’ll take up this term. Here is Mixxx doing its thing. However I am using Ardour to actually do the crossfading …

Mixxx with Super Cross Fader

The Super Crossfader

How is this achieved ? Well Ardour is using a Crossfader plugin. To get this working I needed to setup a Bus much like it is in the Pioneer mixer above …

Ardour Super Mixer Jack Connections

QJackCtl Connections

Notice how the Mixxx decks are routed into Ardour. Then they are routed into a 4 channel (2 x stereo channels) Bus. Here a LADSPA Crossfader plugin cross fades between these two sets of channels. The result goes straight to master out. Notice the monitor channel as well. This can be used to do what DJ’s usually do with headphones when they are mixing :) Here is the main Ardour window …

Ardour Super Mixer

Ardour Tracks

Here is the Ardour Mixer. Notice the 4 channels on the bus …

Ardour Super Mixer Faders Crossfader Plugin

Ardour Mixer

Here is the Crossfader plugin in action (animated GIF). Keep an eye on the channels in the bus as they switch from hard left (Mixx deck 1 is audible) to centered (both decks mixed together) and hard right (only Mixx deck 2 is audible). Of course the slider can be placed anywhere on its path just a like a normal DJ crossfader :)

Ardour Super Mixer Crossfader ANI

Ardour Super DJ Mixer

This is a major breakthrough for my DJ mixing as this means much better control over multi-channel mixing. Obviously we can pull in more than just the two channels from Mixxx here ! Plus, just as in a traditional studio, the mix can be recorded for later editing and fine adjustment, including the cross fades !

The next stage is to setup a quick way of switching the various channels into the crossfader plugin, just as is done with the Pioneer mixer A/B buttons (see above). The crossfader can also be controlled with MIDI and OSC.

But there is one small problem here. The plugin I have used is very simple and does not have any way of controlling the cross fader curve. There is noticeable fluctuation of volume as the channels are mixed together. So I’m gonna find a better plugin or contact the plugin author.

Bottom line here: Jack Audio Connection kit and Ardour are well worth learning as they open up HUGE possibilities to the 21st century DJ. Mixxx is a great way to start with digital DJ’ing, however it’s worth understanding that Jack and Ardour are not just for traditional studio or music composing and recording work, although they do that very well. Combinations of Mixxx, Jack and Ardour can create what is a Super Mixer. We are now entering the age of the Linux audio SUPER MIXER !!! Ma ha ha !

UPDATE May 6th 2013: Got talking to a guy on the #ardour freenode channel. Went back there a couple of hours later and this guy had *written a plugin for me* ! Here: … Turns out he is a lecturer at the University of Paris in Media-Art – – He contributes to many projects and co-organises the Linux Audio Conference. He really seems to have “got” what I’m innovating here, or at least that I’m doing something practical and worthwhile :) What a guy ! So, on with the set up !

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