Denon DJ Prime 4 - Research / Analysis

Tēnā koutou! This document is where you can find all my notes on reverse-engineering the Prime 4's protocols - particularly with the screens.

I'm currently working on a mapping to support the Prime 4 in Mixxx, which is going pretty well so far. However, there currently isn't a way to control the screens on the Prime 4 using MIDI messages. It should definitely be possible to control the screens somehow, as both Serato and Virtual DJ can do it. My goal is to try and figure out how it's done, and document my findings here so we don't have to worry about relying on closed-source solutions that will inevitably run out of support.

TODO list

• Main 10" touch-screen

Helpful Resources

This GitHub repo by TheKikGen contains a lot of useful information about various pieces of DJ hardware that run some form of Engine DJ OS.

This page in Virtual DJ's manual states that the Prime 4 first downloads a custom Virtual DJ skin from the internet when Virtual DJ is launched with the Prime 4 connected for the first time. This means the skin must be in the Prime 4's filesystem somewhere after download, and should be accessible on an SSH-enabled Engine DJ OS image for further analysis.

This GitHub repo by icedream explains how to extract the Engine OS software and enable SSH on it, so you can poke around on the Prime 4's filesystem as much as you like.

This wiki page on the Mixxx GitHub repo explains how to use Wireshark to sniff packets being sent to and from DJ hardware (e.g. the Prime 4), particularly when using proprietary DJ software on a Windows VM. (Yep, we're gonna MITM some DJ gear!)

How to MITM the Prime 4 using Wireshark

Admittedly, I had a bit of trouble figuring out how to do this, so I'm collating all the necessary information here to simplify the process for anyone else wanting to do this. For context: I'm using the Wireshark GUI on Arch Linux in conjunction with Virtual DJ and MIDI-OX running in a Windows virtual machine.

Instructions

• Install Wireshark (sudo pacman -S wireshark-cli wireshark-qt)
• Enable USB monitoring in the kernel (sudo modprobe usbmon)
• Run Wireshark with sudo priveleges (sudo wireshark)
• List connected USB devices (lsusb)
• Observe the Bus 00 and Device 00 prefixes before the Numark PRIME 4 devices. Mine says Bus 002 Device 006.
• Select the appropriate usbmon filter in Wireshark based on the Bus number you see. For me, this is usbmon2. Double-clicking will make Wireshark start capturing packets immediately.
• Launch/use any relevant application (e.g. Virtual DJ) to capture its packets to and from the Prime 4.
• Stop capturing by clicking the red square in the top-left of Wireshark's GUI.
• Add the following search filter: usb.src == "x.y.1" or usb.dst == "x.y.1" where x and y represent Bus 00x and Device 00y from the lsusb output.

SysEx Messages

Here, you can find all the information I could gather on the Prime 4's SysEx messages. There isn't a reference manual explaining these, so I'm finding them as I go.

• f0 00 02 0b 7f 08 60 00 04 04 01 02 00 f7 - Returns the position of all the knobs and faders on the Prime 4.

Send specific RGB values to multi-coloured LEDs

• f0 - SysEx header
• 00 02 0b - Denon ID
• 7f - Send message to main control surface
• 08 03 00 - Command to send RGB colour value
• 05 - Number of SysEx bytes left to send before the f7 footer
• <channel> - MIDI channel number of LED minus 1
• <index> - Index of LED
• <red> - Value between 00 and 7f
• <green> - Value between 00 and 7f
• <blue> - Value between 00 and 7f
• f7 - SysEx footer

Jog Wheel Displays

• Unlock left display for SysEx control - f0 00 02 0b 10 08 10 00 00 f7
• Unlock right display for SysEx control - f0 00 02 0b 30 08 10 00 00 f7

Change jog wheel backlight brightness

• f0 - SysEx header
• 00 02 0b - Denon ID
• 10 or 30 - Control the left or right screen respectively
• 08 7c 00 - Command for changing brightness
• 01 - Number of SysEx bytes left to send before the f7 footer
• <brightness> - Value between 00 and 7f
• f7 - SysEx footer

Change colour of jog wheel display element

• f0 - SysEx header
• 00 02 0b - Denon ID
• 10 or 30 - Control the left or right screen respectively
• 08 0b 00 - Command for changing colour of element
• 09 - Number of SysEx bytes left to send before the f7 footer
• <element> - Element to change (See list below for possible values)
• 0* 0* - Opacity level (between 00 00 and 0f 0f)
• 0* 0* - Red level (Same format as above)
• 0* 0* - Green level (Same format as above)
• 0* 0* - Blue level (Same format as above)
• f7 - SysEx footer

Change position of slip/wheel position indicator

• 0e - MIDI code for pitch shift
• e0 or e1 - Address for wheel position or slip position respectively
• <position LSB> - Least significant byte for 14-bit position precision
• <position MSB> - Most significant byte for 14-bit position precision

Possible elements to change

• 00 - Album Art (Cannot change colour, only opacity)
• 01 - Engine DJ OS Logo
• 02 - Platter Position Ring
• 03 - Platter Position Indicator
• 04 - Slip Position Ring
• 05 - Slip Position Indicator
• 06 - Track Progress Ring (No visible change at present)
• 07 - Track Progress Indicator (No visible change at present)
• 08 - Text

Messages used in Virtual DJ

• Show '3' on left wheel screen - f0 00 02 0b 10 08 0a 00 04 01 02 02 10 f7
• Clear left wheel text - f0 00 02 0b 10 08 0a 00 04 01 00 01 00 f7

Show specific elements / change text

• f0 - SysEx header
• 00 02 0b - Denon ID
• 10 or 30 - Control the left or right screen respectively
• 08 0a 00 - Command for changing text
• 04 - Number of SysEx bytes left to send before the f7 footer
• <visible elements A> - See table below
• <visible elements B> - See table below
• 00 - Album artwork index (Requires images to be loaded onto jog wheels, which hasn't been figured out yet)
• <text to display> - See list below for possible values
• f7 - SysEx footer

visible elements A

Value	Slip Ring	Slip Indicator
0* or 4*
1* or 5*	X
2* or 6*		X
3* or 7*	X	X

Value	Background Image	Engine DJ OS Logo	Wheel Position Ring
*0 or *8
*1 or *9	X
*2 or *a		X
*3 or *b	X	X
*4 or *c			X
*5 or *d	X		X
*6 or *e		X	X
*7 or *f	X	X	X

visible elements B

Value	Loop Symbol
0* or 2* or 4* or 6*
1* or 3* or 5* or 7*	X

Value	Overlay Graphic	Text	Beat Jump Symbol
*0 or *1
*2 or *3		X
*4 or *5	X
*6 or *7	X	X
*8 or *9			X
*a or *b		X	X
*c or *d	X		X
*e or *f	X	X	X

text to display

• 00 - 1/64
• 01 - 1/32
• 02 - 1/16
• 03 - 1/8
• 04 - 1/4
• 05 - 1/2
• 06 - 1
• 07 - 2
• 08 - 4
• 09 - 8
• 0a - 16
• 0b - 32
• 0c - 64
• 0d - --
• 0e - A
• 0f - B
• 10 - 3
• 11 - 6
• 12 - 12
• 13 - C
• 14 - D

FX OLED Screens

Messages used in Serato

• Sending f0 7e 00 06 01 f7 to the Prime 4 returns a long message. Not sure what this means yet.

Send progress bars to OLED screens

• f0 - SysEx header
• 00 02 0b - Denon ID
• 00 08 09 00 - Command to send progress bar
• 09 - Number of SysEx bytes left to send before the f7 footer
• <screen index> - Select screen to send message to (value between 0x00 and 0x07)
• <bar width> - Width of total bar to draw (value between 0x00 and 0x7f)
• <vertical size> - Height of total bar to draw (value between 0x00 and 0x03)
• 01 - (Haven't figured out this one yet)
• <primary brightness> - Brightness of filled bar section (0x00 = black, 0x01 = white, 0x02 = light grey, 0x03 = dark grey) [Needs more investigation]
• <background brightness> Brightness of unfilled bar section (same format as <primary brightness>)
• <vertical position> - Vertical position of bar from top to bottom (0x00 to 0x03 respectively)
• <progress A> - Where to start filling in the bar (between 0x00 (left side) and <bar width> (right side))
• <progress B> - Where to stop filling in the bar (same format as <progress A>)
• f7 - SysEx footer

Send text to OLED screens

• f0 - SysEx header
• 00 02 0b - Denon ID
• 00 08 08 00 - Command to send text
• <message length> - Number of SysEx bytes left to send before the f7 footer
• <screen index> - Select screen to send message to (value between 0x00 and 0x07)
• <text size> - Size of text to be drawn on screen (value between 0x00 and 0x03)
• <text alignment> - Align text to the left (0x00), centre (0x01), or right (0x02) of the screen
• <vertical position> - Vertical position of text from top to bottom (0x00 to 0x03 respectively)
• <text bytes> - Text is sent using ASCII bytes
• f7 - SysEx footer

VU Meters

After some packet-sniffing of the Prime 4 with Virtual DJ, I have found the MIDI messages that control the VU meters of the 4 channels.

b0 / b1 / b2 / b3

This first MIDI byte is a Control Change (CC) byte that determines which mixer strip's VU meter to control.

0a

This second MIDI byte is the address of the VU meters themselves.

The third MIDI byte controls the 'volume' displayed by the VU meters. Below is a visual representation of what each value shows on the VU meters.

• ^ = Blue LED (OFF)

• & = Blue LED (ON)

• = = White LED (OFF)

• # = White LED (ON)

• * = Green LED (OFF)

• $ = Green LED (ON)

• 00 - ^===****** 0

• 01 - ^===*****$ 1

• 02 - ^===****$* 2

• 03 - ^===***$** 3

• 04 - ^===**$*** 4

• 05 - ^===*$**** 5

• 06 - ^===$***** 6

• 07 - ^==#****** 7

• 08 - ^=#=****** 8

• 09 - ^#==****** 9

• 0A - &===****** 10

• 0B - ^===****** 11

• 0C - ^===****** 12

• 0D - ^===****** 13

• 0E - ^===*****$ 14

• 0F - ^===*****$ 15

• 10 - ^===****$$ 16

• 11 - ^===***$*$ 17

• 12 - ^===**$**$ 18

• 13 - ^===*$***$ 19

• 14 - ^===$****$ 20

• 15 - ^==#*****$ 21

• 16 - ^=#=*****$ 22

• 17 - ^#==*****$ 23

• 18 - &===*****$ 24

• 19 - ^===*****$ 25

• 1A - ^===*****$ 26

• 1B - ^===****$$ 27

• 1C - ^===****$$ 28

• 1D - ^===****$$ 29

• 1E - ^===***$$$ 30

• 1F - ^===**$*$$ 31

• 20 - ^===*$**$$ 32

• 21 - ^===$***$$ 33

• 22 - ^==#****$$ 34

• 23 - ^=#=****$$ 35

• 24 - ^#==****$$ 36

• 25 - &===****$$ 37

• 26 - ^===****$$ 38

• 27 - ^===****$$ 39

• 28 - ^===***$$$ 40

• 29 - ^===***$$$ 41

• 2A - ^===***$$$ 42

• 2B - ^===***$$$ 43

• 2C - ^===**$$$$ 44

• 2D - ^===*$*$$$ 45

• 2E - ^===$**$$$ 46

• 2F - ^==#***$$$ 47

• 30 - ^=#=***$$$ 48

• 31 - ^#==***$$$ 49

• 32 - &===***$$$ 50

• 33 - ^===***$$$ 51

• 34 - ^===***$$$ 52

• 35 - ^===**$$$$ 53

• 36 - ^===**$$$$ 54

• 37 - ^===**$$$$ 55

• 38 - ^===**$$$$ 56

• 39 - ^===**$$$$ 57

• 3A - ^===*$$$$$ 58

• 3B - ^===$*$$$$ 59

• 3C - ^==#**$$$$ 60

• 3D - ^=#=**$$$$ 61

• 3E - ^#==**$$$$ 62

• 3F - &===**$$$$ 63

• 40 - ^===**$$$$ 64

• 41 - ^===**$$$$ 65

• 42 - ^===*$$$$$ 66

• 43 - ^===*$$$$$ 67

• 44 - ^===*$$$$$ 68

• 45 - ^===*$$$$$ 69

• 46 - ^===*$$$$$ 70

• 47 - ^===*$$$$$ 71

• 48 - ^===$$$$$$ 72

• 49 - ^==#*$$$$$ 73

• 4A - ^=#=*$$$$$ 74

• 4B - ^#==*$$$$$ 75

• 4C - &===*$$$$$ 76

• 4D - ^===*$$$$$ 77

• 4E - ^===*$$$$$ 78

• 4F - ^===$$$$$$ 79

• 50 - ^===$$$$$$ 80

• 51 - ^===$$$$$$ 81

• 52 - ^===$$$$$$ 82

• 53 - ^===$$$$$$ 83

• 54 - ^===$$$$$$ 84

• 55 - ^===$$$$$$ 85

• 56 - ^==#$$$$$$ 86

• 57 - ^=#=$$$$$$ 87

• 58 - ^#==$$$$$$ 88

• 59 - &===$$$$$$ 89

• 5A - ^===$$$$$$ 90

• 5B - ^===$$$$$$ 91

• 5C - ^==#$$$$$$ 92

• 5D - ^==#$$$$$$ 93

• 5E - ^==#$$$$$$ 94

• 5F - ^==#$$$$$$ 95

• 60 - ^==#$$$$$$ 96

• 61 - ^==#$$$$$$ 97

• 62 - ^==#$$$$$$ 98

• 63 - ^==#$$$$$$ 99

• 64 - ^=##$$$$$$ 100

• 65 - ^#=#$$$$$$ 101

• 66 - &==#$$$$$$ 102

• 67 - ^==#$$$$$$ 103

• 68 - ^==#$$$$$$ 104

• 69 - ^=##$$$$$$ 105

• 6A - ^=##$$$$$$ 106

• 6B - ^=##$$$$$$ 107

• 6C - ^=##$$$$$$ 108

• 6D - ^=##$$$$$$ 109

• 6E - ^=##$$$$$$ 110

• 6F - ^=##$$$$$$ 111

• 70 - ^=##$$$$$$ 112

• 71 - ^=##$$$$$$ 113

• 72 - ^###$$$$$$ 114

• 73 - &=##$$$$$$ 115

• 74 - ^=##$$$$$$ 116

• 75 - ^###$$$$$$ 117

• 76 - ^###$$$$$$ 118

• 77 - ^###$$$$$$ 119

• 78 - ^###$$$$$$ 120

• 79 - ^###$$$$$$ 121

• 7A - ^###$$$$$$ 122

• 7B - ^###$$$$$$ 123

• 7C - ^###$$$$$$ 124

• 7D - ^###$$$$$$ 125

• 7E - ^###$$$$$$ 126

• 7F - &###$$$$$$ 127

NOTE: As far as I'm aware, the Master L + R channels are not controlled by MIDI. They are instead controlled by the audio sent through the Prime 4's soundcard when in Computer Mode. As long as your audio is configured to go through the Prime 4, the Master L + R meters should behave as expected automatically.