DecaBox - DMX to MIDI Conversion

Lighting consoles can easily control nearly any type of MIDI gear.

Basic System Information

decabox-large-2.jpg

This firmware personality for the DecaBox receives DMX lighing data and generates a series of MIDI messages. It allows easy control of MIDI equipment, such as audio equipment, sound effects generators and other show control elements.

The DecaBox USB port is used for firmware updates.  It does not transmit MIDI data. 

Originally, the lighting guys wanted to keep their wiring separate from the audio crew, who were using XLR-3 microphone cable; thus the 5 pin lighting data standard.  However, in nearly every current implementation of DMX control only pins 1, 2 and 3 are used. The 5 pin connectors cost about $2 more in quantity, so some manufacturers eschew them for less expensive 3 pin versions.  Professional and touring gear still relies nearly exclusively on the 5 pin infrastructure. In either case, pin 1 is ground, pin 2 is ‘data complement’ or D- and pin 3 is ‘data true’ or D+. 




Output Modes

For convenience here, a PC-based DMX output utility was used to generate various DMX channel:value pairs.

Using the built-in LCD, set the operating mode and DMX start address for the system. Different modes require varying quantities of DMX data, as described below. In the charts below, 'Channel 1' means 'system start address'. So if the DecaBox is set to start address 10, channel 1 means channel 10. Make sense?

The word channel means something different in the MIDI and DMX worlds.  A MIDI channel is most easily compared to a DMX universe. Messages in a single MIDI channel can contain note on / note off information, continuous controller data, patch change messages, etc. However, a single MIDI cable can contain data for all 16 MIDI channels while a DMX cable only controls a single universe [512 DMX channels] of data.

Also, MIDI is a zero-based system. That is, the first MIDI channel is '0' and the last is 15, or 'F' in hex code. Note values and velocities vary between [0 127] or [0x0 0x7F] in hex. In the screen captures below, hex, zero-based data is displayed.

console.png

This simple PC-based DMX controller from ENTTEC allows precise channel:value control for testing.


Mode 1: Everything

This is our most verbose mode. Sixteen sequential DMX channels generate note on / note off pairs for all 128 notes in a MIDI scale, and all 16 channels in the MIDI world. Then an additional 119 channels generate all 119 general-purpose MIDI CC messages.

DMX Channels Required 135
DMX Channel MIDI Output
1 MIDI channel 1, Note on / note off pairs, 128 total notes.
2 MIDI channel 2, Note on / note off pairs, 128 total notes.
...  
16 MIDI channel 16, Note on / note off pairs, 128 total notes.
17 MIDI CC #0, values [0 127].
... ...
Channel 136 MIDI CC #128, values [0 127].

 

midi-notes.png

Here DMX channel 1 fader was run somewhat smoothly from 0 to 100%. The entire MIDI scale, with some skipping due to how quickly the fader moved, is represented.

cc-1.png

Here DMX channel 17 fader was moved. This corresponds to MIDI CC #0, 'Bank Select MSB.'

 

Mode 2: Easy Note & CC Messages

Mode 2 is very compact: 2 sequential DMX channels generate all note on / note off pairs for MIDI channel 1 and MIDI CC #0.

DMX Channels Required 2
DMX Channel MIDI Output
1 MIDI channel 1, Note on / note off pairs, 128 total notes.
2 MIDI CC #0, values [0 127].

mode1.png

Again, values are missing because the fader was run quickly between [0 100%]. However, all values are available.

Mode 3

Mode 3 is a happy medium: Two sequential DMX channels generate note on / note off pairs for all 128 notes in a MIDI scale on MIDI channels 1 & 2. Then an additional 6 channels generate the first 6 general-purpose MIDI CC messages.

DMX Channels Required 8
DMX Channel MIDI Output
1 MIDI channel 1, Note on / note off pairs, 128 total notes.
2 MIDI channel 2, Note on / note off pairs, 128 total notes.
3 MIDI CC #0, values [0 127].
... ...
8 MIDI CC #6, values [0 127].

 

Mode 4: Program Change / Patch Change Messages

Simple, here. 16 DMX channels generate all patch change / program change messages on MIDI channels [1 16]

DMX Channels Required 16
DMX Channel MIDI Output
1 MIDI program change, MIDI channel 1
... ...
16 MIDI program change, MIDI channel 16

mode4.png

Mode 4 data, showing PC messages sent on MIDI channels 1, 2, 3 and 10.

 

Mode 5: Note On / Note Off With Fixed Velocities

Simple, here. 128 DMX channels generate 'note on' messages when DMX values are 100% and 'note off' messages when values are 0%. A popular TV show requested this mode for triggering sound effects via bump buttons on a console.

DMX Channels Required 128
DMX Channel MIDI Output
1 @ 100% MIDI channel 1, MIDI note 1, ON
1 @ 0% MIDI channel 1, MIDI note 1, OFF
... ...
128 @ 100% MIDI channel 1, MIDI note 128, On

mode5.png

 

Purchasing

If you've landed here via a web search, don't already own one of these systems, but would like to add one to your collection, our online store is here:

www.response-box.com/gear/shop

And our main site is here, which includes links to distributors, etc:

www.response-box.com/gear