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Midi Crash Course
MIDI (Musical Instrument Digital Interface) is a standard for electronic musical devices to communicate. This page is a brief introduction to MIDI that should explain what you need to know to map MIDI controllers to Mixxx.
MIDI is a widely used standard that a lot of hardware and software support. It dates back to the 1980s when it was used to make synthesizers, samplers, and sequencers communicate. These older devices used cables with 5-pin DIN connectors to carry MIDI signals. Most MIDI devices today send the MIDI signals over a USB cable. Some modern devices can also can use cables with the 5-pin DIN connectors. DJ controllers with these 5-pin DIN connectors do not ordinarily use them to send signals to the computer; they are used to communicate via MIDI with other gear and the ability to use MIDI without being plugged into a computer (although they need to be plugged into another power source without a USB cable supplying power).
Controllers that comply with the USB MIDI class standard (also called "class compliant" devices) do not require any special drivers. Most controllers are USB MIDI class compliant, but not all. See the Mixxx DJ Hardware Guide for information about particular controllers.
Mixxx displays the numbers in MIDI signals in hexidecimal. If you are unfamiliar with hexidecimal numbers, read this tutorial.
Most MIDI messages are three bytes long. The first byte of any MIDI
message is called the Status byte. The first nybble (hex digit) is
the op-code and the second is the MIDI channel number. So if you have
0x90
the op-code is 0x9
and the channel number is 0x0
(Ch 1.) The
full list of MIDI messages is below, where n represents the channel
number (0..F inclusive):
Status | Function | Data bytes | |
---|---|---|---|
0x8n | Note off | Note number | Note velocity |
0x9n | Note on | Note number | Note velocity |
0xAn | Polyphonic after-touch | Note number | Amount |
0xBn | Control/mode change | Control number | Value |
0xCn | Program change | Program number | (n/a) |
0xDn | Channel after-touch | Amount | (n/a) |
0xEn | Pitch wheel | LSB | MSB |
0xF0 | System Exclusive message | Vendor ID | (data) |
0xF1 | MIDI Time Code Qtr. Frame | (see spec) | |
0xF2 | Song Position Pointer | LSB | MSB |
0xF3 | Song Select | Song number | (n/a) |
0xF4 | Undefined | ||
0xF5 | Undefined | ||
0xF6 | Tune request | (n/a) | |
0xF7 | End of SysEx (EOX) | (n/a) | |
0xF8 | Timing clock | (n/a) | |
0xF9 | Undefined | (n/a) | |
0xFA | Start | (n/a) | |
0xFB | Continue | (n/a) | |
0xFC | Stop | (n/a) | |
0xFD | Undefined | (n/a) | |
0xFE | Active Sensing | (n/a) | |
0xFF | System Reset | (n/a) |
The boldface entries in the table above are the messages we are most concerned with since most DJ controllers use only these for all functions. You'll need to consult the MIDI spec for the DJ controller you're working with to determine which messages and note/control numbers correspond to the DJ controller functions & LEDs. If your controller's MIDI spec gives only note names and not numbers, use this table to convert them. To convert from decimal to hex, use this.
(Note that in order to use System Exclusive messages, you will need MIDI Scripting.)
First, try using the MIDI Learn functionality in the Preferences->MIDI Devices window at the bottom. It will help you get many of the essential functions mapped quickly without having to manually edit XML.
An explanation of the MIDI signals that your controller sends to computers and how it reacts to MIDI signals that computers send to it should be available from the controller manufacturer. This is likely in a document on the product page for your controller on the manufacturer's website or in the support section of the website. If it is not in a separate document, it is likely at the end of the manual.
Unfortunately, some manufacturers do not provide this information. In that case, you have to see what signals the controller sends to be able to map it, which you can do with Mixxx. Even if the manufacturer does provide MIDI documentation, it may be easier to sniff your controller with Mixxx than keep looking up numbers in the documentation.
- Start Mixxx from a command prompt using the
--midiDebug
option like so:
- Linux:
user@machine:~$ mixxx --midiDebug
- Windows:
C:\Program Files\Mixxx>mixxx --midiDebug
- Mac OSX:
$ open -a mixxx --args --midiDebug
- Look at the output
- Watch the console output or look at the Mixxx.log file which will contain all of the MIDI messages Mixxx receives. As you manipulate the controller, the MIDI commands it sends will be printed to the screen/logged to the file. Compare the status (first) byte in each line with the table above and note which button/slider/control sends what message.
- For example, when you move a slider, you might see
Debug: [...]: "MIDI ch 1: opcode: B0, ctrl: 2, val: 3D" Debug: [...]: "MIDI ch 1: opcode: B0, ctrl: 2, val: 3A" Debug: [...]: "MIDI ch 1: opcode: B0, ctrl: 2, val: 3D" Debug: [...]: "MIDI ch 1: opcode: B0, ctrl: 2, val: 3B" Debug: [...]: "MIDI ch 1: opcode: B0, ctrl: 2, val: 3C"
In this instance, it's sending 0xB0 (which when we look at the table above, we see that it's a Control Change message on channel 1) We also see that the second byte, 0x02 in this case, is the control number that was moved, and the third is the value or position of that control, which you can ignore for the purposes of mapping.
- Add the byte values to a
<control>
block in the XML file
- Just plug the first two bytes into a
<control>
XML block for<status>
and<midino>
respectively. This is detailed in the next section.
Open a console and issue amidi -l
. This will list the attached MIDI
device(s) like so:
Dir Device Name
IO hw:1,0,0 SCS.3d MIDI 1
Then, to dump the data, you just issue amidi -p hw:1,0,0 -d
(Replace
hw:1,0,0 with whatever device ID your controller shows in the list.)
You'll get output like this:
B0 02 3D
B0 02 3A
B0 02 3D
B0 02 3B
B0 02 3C
See above for how to interpret this data.
The program aseqdump
works similarly, but is a bit more verbose than a
series of hexidecimal numbers:
$ aseqdump -l
Port Client name Port name
0:0 System Timer
0:1 System Announce
14:0 Midi Through Midi Through Port-0
20:0 Tweaker Tweaker MIDI 1
20:1 Tweaker Tweaker MIDI 2
$ aseqdump -p 20:0
Waiting for data. Press Ctrl+C to end.
Source Event Ch Data
20:0 Note on 0, note 1, velocity 127
20:0 Note off 0, note 1
20:0 Note on 0, note 2, velocity 127
20:0 Note off 0, note 2
20:0 Note on 0, note 3, velocity 127
20:0 Note off 0, note 3
You can download tail.exe to
watch mixxx.log as
new messages are added or build Mixxx with
scons msvcdebug=1
and run it with the --midiDebug
option. This will
cause it to pop up a console window when you run it and the MIDI
messages received by your controller will be displayed there.
Download the free MIDI Monitor utility and run it. MIDI Monitor is a utility for Mac OS X which displays MIDI signals in a variety of formats. It can watch both incoming and outgoing MIDI streams, and can filter them by message type and channel.
Download the free MIDISimulator utility and run it. MidiSimulator is a tool to test midi devices like pianos or dj controllers. It allows you to receive and send midi events.
Mixxx is a free and open-source DJ software.
Manual
Hardware Compatibility
Reporting Bugs
Getting Involved
Contribution Guidelines
Coding Guidelines
Using Git
Developer Guide
Contributing Mappings
Mixxx Controls
MIDI Scripting
Components JS