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.
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, not every manufacturer provides this information.
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):
|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)|
|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)|
|0xF7||End of SysEx (EOX)||(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.)
Every controller works differently, but these are some typical patterns.
0x9, value of
0x9, value of
0x8, value of
If there's an LED behind the button, that is typically controlled by sending a message to the controller with the same first two bytes (status and note number) that the controller sends when the button is pressed. As for the value byte, for LEDs that can only be turned on or off, typically
0x00 turns it off and
0x7F turns it on. For multi-color LEDs, the color is typically controlled by sending different values. Which ones correspond to which colors should be in the MIDI specification document for your controller. If they are not, you will have to look at mappings for other DJ software, or just try a few different values.
These usually send messages with an op-code of
0xB and a value corresponding to the absolute position of the knob or slider (between
Endless knobs/encoders (that you can turn continuously) typically send messages with an op-code of
0xB and the value only indicates whether the encoder is being turned left or right (
These usually operate exactly like endless knobs/encoders above, and they usually also send messages just like buttons above when they're touched or released which is intended to mark when scratching begins and ends respectively.
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.
Unfortunately, some manufacturers do not provide information about the MIDI signals used by the controllers they make. 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 controller's documentation.
--controllerDebugoption like so:
[email protected]:~$ mixxx --controllerDebug
C:\Program Files\Mixxx>mixxx --controllerDebug
$ open -a mixxx --args --controllerDebug
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.
<control>block in the XML file
<control>XML block for
<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.
amidi can also be used to send MIDI messages to your controller with the -S option. Specify each byte as a hexadecimal number and separate the bytes by spaces. For example:
amidi -p hw:1,0,0 -S "b0 02 7f"
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
--controllerDebug 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.