1. Digital Multiplex
In the early years of lighting, proprietary communication
protocols were pretty much the only way to talk to
your dimmer racks from your lighting console. Every
manufacturer had their own language, which, as you can
imagine, made it really hard to mix and match gear without
a third "interpreter". While there were some interpreting
pieces of gear out there, it wasn't until 1986 when the
Engineering Commission of United States Institute for
Theatre Technology (USITT) created Digital Multiplex, or
DMX for short. Driven by the emergence of new "intelligent
lights" and the desire to have different brands play nice
with each other, we finally had a standard language for all
lighting products to speak.
DMX in More Detail
DMX communicates 512 channels of information
to everything it is connected to. Every channel is
communicating a simple value somewhere between 0 and
255 which we often convert to a percentage of 0-100%.
We tell a fixture or dimmer rack what channels we want it to
listen to by addressing the fixture/dimmer. For example, if
you have a 4 channel dimmer pack addressed to channel 1,
it will look for the values on channels 1-4 and provide power
to the fixtures plugged in at the value you've sent it. An
LED fixture in 4 channel mode (Red, Green, Blue, Intensity)
addressed to channel 101 will look for data in channels
101-104. Depending on how the manufacturer sets up their
firmware, it may see a value for Red in channel 101, Green
in 102, Blue in 103 and overall intensity in 104. You tell any
given fixture or dimmer which channels it should take its
values from and it will, simple as that.
DMX travels to fixtures or dimmers via DMX cable which
has 120 ohm resistance (as opposed to mic cable which
has 75 ohm resistance) and uses either 3 pin or 5 pin XLR
connectors. DMX is digital data, so we use cable designed
for digital data, not analog mic cables.
DMX Controllers
So if DMX is just a conduit of information, what generates
those values for each of the 512 channels? Your lighting
console handles that job, and sort of serves as a highly
sophisticated universal remote. A lighting controller works
the same way except it simply says, "OK input 1, set your
value to 255. Input 2, to 128. Input 3, to 0." It does this for
all 512 channels constantly, updating the values it sends
as you tell it to. And if a fixture has multiple channels of
information, it's just like having more features available on
the remote for that specific source.
Practical Applications
One of the beautiful things about DMX is that you can
hook up your fixtures in any order and as long as they are
all addressed properly, they'll all get the values they are
looking for. DMX is meant to be daisy-chained, though it's
recommended that you don't daisy chain more than 30
fixtures together. If you have more than 30 fixtures or your
fixtures are spread out so far that daisy-chaining them isn't
practical, you can buy an opti-splitter to distribute DMX
safely and completely to all of your fixtures. It's also highly
recommended that you terminate your DMX line with a
DMX terminator. DMX moves information at a high speed
so it's critical to give it the best signal path possible free
from interference and the possibility of getting bogged
down. Too many fixtures on one chain, not having your line
terminated and using microphone cable instead of DMX
(both DMX and microphone cables use the same 3-pin
connectors) are all things that can cause interference in
your communication. Interference results in lights doing
"interesting" things. Your fixtures may still be receiving data,
it's just not always the correct data.
Hopefully, that clears up any questions or confusion that
revolves around DMX for you. It's really as simple as being
a conduit of 512 channels of information, and it's a critical
component to making your lighting systems work. Set up
correctly, you will have the power and control to do great
things with your lighting.
We're always here to assist if you need help setting up or
building a new lighting system.
Next to questions about upgrading their sound system, the most common question churches ask us is how to
create an engaging environment through lighting. Before we dive too deep into fixtures and what to do with them,
we need to back up a step and discusWs one of the more misunderstood topics we come across: DMX. You may
know it is key to controlling your lights, but what really is DMX? Let's dive in.
Lighting 101: Demystifying DMX
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Blizzard Lighting AnyFi
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JANDS Vista Serives
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