American Cinematographer - May 2013 - 66

The ABCs of

DMX

Lighting professionals explain how
DMX technology has transformed
soundstage work.
By Benjamin B
•|•

T

his article offers an introduction to DMX technology,
the foundation of many lighting-control systems used
on soundstages today. It is divided into three parts: the
basics, a few sample setups using low-cost tools, and a
discussion of DMX applications on large film sets. To learn
about DMX, I sought out many knowledgeable practitioners
in London and Paris: Yanne Blitte, Marie-José Collet, Steve
Howard, Chris Millard and Ian Sherborn at Panalux; gaffers
John “Biggles” Higgins and Reuben Garrett; lighting-desk
programmer Stephen Mathie; and director of photography
Philippe Rousselot, ASC, AFC.
DMX Basics
The DMX512 protocol, or DMX for short, was
created in 1986 by lighting professionals who wanted to give
manufacturers and users a simple, universal digital standard
for lighting control. DMX was adopted throughout the
industry, and became formalized in 1990. It became an ANSI
standard in 2004 (officially referred to as DMX512-A).
According to Millard, the rapid adoption of DMX was due in
large part to the rock ’n’ roll stadium tours done in the 1980s
by bands such as The Rolling Stones. He notes, “The lighting crews were working with equipment from different
manufacturers from around the world, and they had to set up
working systems in all these different venues. It was a nightmare before DMX.”
DMX stands for Digital Multiplex. It is a digital signal
protocol; it defines the syntax of a signal that is sent by lighting controllers to fixtures and peripherals such as dimmers.
The DMX protocol defines a universe as 512 channels. A

66

May 2013

single DMX cable transmits only one universe, so sophisticated applications, including big film sets, often require
multiple universes. The DMX signal is simple, consisting of a
header followed by up to 512 channels of data. Each channel
includes 8 bits of data, representing a value between 0 and
255. Each of the 512 channel values is refreshed 44 times a
second. The bandwidth required for DMX is 180 kbits/sec.
Typically, a channel is allocated to an individual light
fixture, and the channel value represents its dimming level.
For example, sending a value of 127 to channel 3 could mean
that fixture 3 is dimmed to 50 percent, while sending a value
of 255 would set fixture 3 at 100 percent. Many LED fixtures
have three channels for individual control of red, green and
blue. As we shall see, some complex units, like automated
lights, actually use multiple channels, with values that can
represent color and position as well as dimming level. Most
DMX units have simple rotary or push buttons that allow
users to set the channel (or the start channel, in the case of
multiple channels) for the unit. The channel number is arbitrary, but is usually set according to a mnemonic numbering
scheme.
Howard notes that DMX can be used to control equipment other than lights, including fog machines and video
servers.
DMX requires two conductors for positive and negative signals, typically about 5 volts, plus ground shielding. The
positive represents a digital 1, and the negative a 0. Although
the norm specifies a 5-pin XLR cable (a.k.a. XLR-5), lowcost units sometimes use 3-pin XLRs, which are officially
prohibited. (One danger is that an XLR-3 might be plugged
into an audio board with 48 volts of phantom power by
mistake, which could damage DMX circuitry.)
The DMX spec recommends maximum lengths of
about 500 meters, with no more than 32 devices attached;
additional units can be added by using DMX switches or
amplifiers. A simple DMX network is in the form of a daisy
chain: a single cable routes the data signal from unit to unit.
Sophisticated applications send multiple DMX universes
down a single Ethernet cable. Sherwood notes, “In the 1980s,
512 channels was all you needed for a Rolling Stones concert,
but today we’re seeing productions with 30,000 channels!”

American Cinematographer



American Cinematographer - May 2013

Table of Contents for the Digital Edition of American Cinematographer - May 2013

American Cinematographer - May 2013
Contents
Editor’s Note
President’s Desk
Short Takes: “Suit & Tie”
Production Slate: Trance • The Reluctant Fundamentalist
Surviving the Future
A Trailblazer’s Tale
Conjuring Hope
The ABCs of DMX
Star Tech
Hot Shots
New Products & Services
International Marketplace
Classified Ads
Ad Index
Clubhouse News
ASC Close-Up: Paul Maibaum
American Cinematographer - May 2013 - American Cinematographer - May 2013
American Cinematographer - May 2013 - Cover2
American Cinematographer - May 2013 - 1
American Cinematographer - May 2013 - 2
American Cinematographer - May 2013 - Contents
American Cinematographer - May 2013 - 4
American Cinematographer - May 2013 - 5
American Cinematographer - May 2013 - 6
American Cinematographer - May 2013 - 7
American Cinematographer - May 2013 - 8
American Cinematographer - May 2013 - 9
American Cinematographer - May 2013 - Editor’s Note
American Cinematographer - May 2013 - 11
American Cinematographer - May 2013 - President’s Desk
American Cinematographer - May 2013 - 13
American Cinematographer - May 2013 - Short Takes: “Suit & Tie”
American Cinematographer - May 2013 - 15
American Cinematographer - May 2013 - 16
American Cinematographer - May 2013 - 17
American Cinematographer - May 2013 - 18
American Cinematographer - May 2013 - 19
American Cinematographer - May 2013 - Production Slate: Trance • The Reluctant Fundamentalist
American Cinematographer - May 2013 - 21
American Cinematographer - May 2013 - 22
American Cinematographer - May 2013 - 23
American Cinematographer - May 2013 - 24
American Cinematographer - May 2013 - 25
American Cinematographer - May 2013 - 26
American Cinematographer - May 2013 - 27
American Cinematographer - May 2013 - 28
American Cinematographer - May 2013 - 29
American Cinematographer - May 2013 - 30
American Cinematographer - May 2013 - 31
American Cinematographer - May 2013 - 32
American Cinematographer - May 2013 - 33
American Cinematographer - May 2013 - Surviving the Future
American Cinematographer - May 2013 - 35
American Cinematographer - May 2013 - 36
American Cinematographer - May 2013 - 37
American Cinematographer - May 2013 - 38
American Cinematographer - May 2013 - 39
American Cinematographer - May 2013 - 40
American Cinematographer - May 2013 - 41
American Cinematographer - May 2013 - 42
American Cinematographer - May 2013 - 43
American Cinematographer - May 2013 - 44
American Cinematographer - May 2013 - 45
American Cinematographer - May 2013 - 46
American Cinematographer - May 2013 - 47
American Cinematographer - May 2013 - A Trailblazer’s Tale
American Cinematographer - May 2013 - 49
American Cinematographer - May 2013 - 50
American Cinematographer - May 2013 - 51
American Cinematographer - May 2013 - 52
American Cinematographer - May 2013 - 53
American Cinematographer - May 2013 - 54
American Cinematographer - May 2013 - 55
American Cinematographer - May 2013 - Conjuring Hope
American Cinematographer - May 2013 - 57
American Cinematographer - May 2013 - 58
American Cinematographer - May 2013 - 59
American Cinematographer - May 2013 - 60
American Cinematographer - May 2013 - 61
American Cinematographer - May 2013 - 62
American Cinematographer - May 2013 - 63
American Cinematographer - May 2013 - 64
American Cinematographer - May 2013 - 65
American Cinematographer - May 2013 - The ABCs of DMX
American Cinematographer - May 2013 - 67
American Cinematographer - May 2013 - 68
American Cinematographer - May 2013 - 69
American Cinematographer - May 2013 - 70
American Cinematographer - May 2013 - 71
American Cinematographer - May 2013 - Star Tech
American Cinematographer - May 2013 - 73
American Cinematographer - May 2013 - 74
American Cinematographer - May 2013 - 75
American Cinematographer - May 2013 - 76
American Cinematographer - May 2013 - Hot Shots
American Cinematographer - May 2013 - 78
American Cinematographer - May 2013 - 79
American Cinematographer - May 2013 - 80
American Cinematographer - May 2013 - 81
American Cinematographer - May 2013 - 82
American Cinematographer - May 2013 - 83
American Cinematographer - May 2013 - 84
American Cinematographer - May 2013 - 85
American Cinematographer - May 2013 - 86
American Cinematographer - May 2013 - 87
American Cinematographer - May 2013 - 88
American Cinematographer - May 2013 - 89
American Cinematographer - May 2013 - New Products & Services
American Cinematographer - May 2013 - 91
American Cinematographer - May 2013 - 92
American Cinematographer - May 2013 - 93
American Cinematographer - May 2013 - International Marketplace
American Cinematographer - May 2013 - Classified Ads
American Cinematographer - May 2013 - Ad Index
American Cinematographer - May 2013 - 97
American Cinematographer - May 2013 - Clubhouse News
American Cinematographer - May 2013 - 99
American Cinematographer - May 2013 - ASC Close-Up: Paul Maibaum
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