Alex's Slip-box

These are my org-mode notes in sort of Zettelkasten style

Mixxx, Ardour, JACK and MIDI

Created on May 30, 2022

Updated on June 21, 2022

Tags: midi, linux, audio

:ID: abbff1aa-b163-4f08-ba2c-c7ed8ca8ef12

Do crazy shit with Mixxx, JACK server routing, DAWs with VST plugins and MIDI control on Linux (Ubuntu/Pop_OS).

This is what I want to do:

  • Send each of Mixxx’s 4 deck’s audio streams to a track in Ardour.
  • Add Windows VST plugins as FX on those Ardour tracks.
  • Control the VST plugin FX parameters from a MIDI controller (Xone K2 in my case).
  • WIP Send MIDI clock from Mixxx to Ardour to for the FX (like delay) that can use tempo and beat syncing.
  • Send the 4 Ardour deck tracks out of two audio interfaces (each with 4 outputs) and into a 4 channel hardware mixer (Xone 43 in my case).
  • Send the master mix out of the hardware mixer to an audio interface input to be recorded in Mixxx or Ardour

Here’s how I am doing it:

# My Setup

But first, an explanation of my hardware setup:

See My audio setup

# The software

I use Linux. This is the software I use. Some of the software mentioned here isn’t directly used for this particular project, but I mention here since it’s good to know about it in general for Linux audio production.

# Mixxx

https://mixxx.org/

Free, open source DJ software. Stands up to paid versions and works on Linux. It really is great.

# Developer mode

You can start Mixxx with the --developer flag. In addition to extra logging and a developer menu in the GUI, it also adds the Midi Through Port-0 as an option under Controllers. This is key for sending out MIDI time code from Mixxx without having to depending on a sound card. 

pasuspender -- mixxx --developer

# MIDI for light

The MIDI for light can to send MIDI timecode from Mixxx to wherever you want (like a DAW, FX box, drum machine, lighting rig, etc.)

# Ardour

https://ardour.org/

Full-on DAW that works on Linux. It’s not free (unless you build from source), but it’s a kind of pay what you want model as of writing this. It’s great software and it can be a slave to an external MIDI clock source.

# MIDI Control

  • MIDI sync

# Using Windows VSTs in Linux

Yes, this can be done, although I was only able to get VST3 (not VST 2) to work. I was probably doing something wrong, but I didn’t care, only interested in VST3 anyhow. Doing this requires Wine (see VST plugins section) and yabridge.

# Jack Audio Connection Kit

https://jackaudio.org/

A Sound server. Lets you route audio and MIDI all over the place.

# QjackCtl

https://github.com/rncbc/qjackctl This is a GUI for managing the Jack server.

# MIDI routing

Need to install a2jmidid. This somehow bridges the jack server MIDI port to ALSA MIDI. 

sudo apt-get install a2jmidid

In QjackCtl…

  • add a2jmidid -e & as a execute after startup script. This kicks off a2jmidid and will automatically map your midi controller to jack where it can be routed to a midi input.
  • I also added killall a2jmidid as a shutdown script to clean up after.

Here’s an example from Qjackctl, where I am routing MIDI from my Xone K2 to Reaper. The midi controller will now show up in Reaper in the midi device settings where it can be enabled for input and control.

# Multiple audio interfaces

JACK is designed to support a single audio interface. There are several work-arounds for those of us with several audio interfaces. See also https://jackaudio.org/faq/multiple_devices.html

  • alsa_in / alsa_out

    The alsa_in / alsa_out programs can expose additional audio interfaces to JACK and sync their clocks. It basically works like this:

    1. Get a list of sound cards by cat /proc/asound/cards
    2. Find the name of the sound card
    3. If you need outputs: alsa_out -d hw:NAME_OF_CARD
    4. Just use alsa_in -d to enable inputs
  • zita-ajbridge

    https://kokkinizita.linuxaudio.org/linuxaudio/zita-ajbridge-doc/quickguide.html

    The two CLI tools this provides do the same thing as alsa_in / alsa_out but claims to have better sound quality. I did have better luck with using this to add a second audio interface to JACK.

# Enable Realtime (Optional)

Enabling this can help performance / latency. Most Linux distros have permissions around Realtime scheduling. See https://jackaudio.org/faq/linux_rt_config.html for how to enable it (it’s really not hard).

Then you can check the box “Realtime” in the Jack settings to use it.

# Jack scripting (Optional)

This is just here for reference. It can be useful to do some things via scripts, like make connections between ports in order to automate repetitive tasks. See making connection in jack on the command line.

# snd_virmidi

This is Linux kernel module that can create virtual midi interfaces that appear as sound cards to the system. This isn’t needed for this project, but it’s good to know about.

# snd-seq-dummy

This is a Linux kernel module that can create midi through ports. This is only needed if you don’t already have an ALSA midi through port or you need an extra one for some reason.

# To start it

n = how many ports you want 

sudo modprobe snd-seq-dummy ports=n
  • To make it available after reboots

    Edit /etc/modprobe.d/midi.conf and add line options snd-seq-dummy ports=n

# To unload it

sudo modprobe -r snd-seq-dummy

# Putting it all together

# JACK

# Ardour

# Mixxx

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