Basics 9. Interfaces, universes and network output (Art-Net and sACN)
A computer has no DMX socket, which means a translator is needed between the software and the light. Let’s look at what those translators are, how they differ, and answer the question that comes up for everyone sooner or later: what to do when 512 channels run out.
The USB interface: a dongle between laptop and line
A DMX interface (also called an adapter, a controller, or colloquially a «dongle») is a small box: USB on one side, an XLR socket on the other. The software hands it a packet of 512 values and it generates the correct electrical signal in the cable.
The classes of device you will meet on the market:
| Class | Characteristics |
|---|---|
| Simple uDMX-compatible | Cheap, the size of a memory stick. One output, 512 channels. Enough for a small rig |
| FTDI-based (Open DMX and clones) | Also inexpensive, but the computer generates the signal — under system load the stream can stutter |
| With its own processor (Pro class) | A steady stream regardless of PC load, often with galvanic isolation. Costlier, more reliable |
| Network nodes (Art-Net/sACN node) | Plug into the local network rather than USB; usually 1–4 DMX outputs |
The universe: one line of 512 channels
A universe is one complete DMX line, that is, its 512 channels. One simple USB interface = one universe.
While you have few fixtures the question never arises. Let’s count a typical rig:
| Fixtures | Channels |
|---|---|
| 8 wash lights × 7 channels | 56 |
| 4 spot heads × 16 channels | 64 |
| 2 strobes × 3 channels | 6 |
| Hazer | 2 |
| Total | 128 out of 512 |
A fourfold margin — it all lives comfortably in one universe. Now take a club with pixel bars: eight bars at 96 channels each is already 768 channels, and they physically will not fit into one line.
Signs that you need a second universe:
- the total channel count of your fixtures has passed 512;
- you have more than 32 fixtures (the limit of one line, from lesson eight);
- the fixtures are far apart and running cable between them is awkward;
- some of the gear connects only over the network.
How to get several universes
Option 1. Several USB interfaces. Simple and cheap: two dongles, two universes. The downside is that the cables from each run to different ends of the venue, and laptops do not have many USB ports.
Option 2. A multi-port interface. One box with several DMX outputs.
Option 3. Network output. The computer sends the data into an ordinary local network, and nodes (Ethernet → DMX boxes) are placed around the venue. This is the standard solution for large spaces: a single network cable runs across the room and the nodes sit where the fixtures are.
Art-Net and sACN: two languages for the network
Both protocols do the same thing — they carry DMX packets over an ordinary computer network. For a beginner the differences are minor, but worth knowing.
| Art-Net | sACN (E1.31) | |
|---|---|---|
| Age and reach | Older, supported by almost everything | Newer, the standard for large installations |
| How it sends data | Broadcast, or to a specific address | Multicast |
| Universe numbering | Historically from 0 | From 1 |
| Network load | Higher when broadcasting | Lower, the network distributes it more intelligently |
What you need to know about networking to make it work
You do not have to be a network engineer here — four rules are enough.
- The computer and the node must be on the same subnet. In plain terms, their IP addresses must start the same way:
192.168.0.10on the laptop and192.168.0.50on the node, for example. If the node’s address looks like2.0.0.20, give the laptop an address from the same series or reconfigure the node. - Wired network only. Wi-Fi for lighting can introduce latency and packet loss, which turns into jerky light. An ordinary cable and an inexpensive switch are more dependable. Wi-Fi lighting has its own specific applications.
- Disable unused network adapters while you work, and allow the software through the Windows firewall. More than half of all «the network is there but the light is not» problems are the firewall.
- Do not mix the lighting network with the office one. Ideally a dedicated switch for lighting only: no stray traffic, no surprises from other people’s devices.
Wireless DMX and RDM
Wireless DMX (W-DMX, CRMX and similar) is a transmitter-and-receiver pair on a radio link. It is indispensable when cable cannot be run: lighting on the ceiling, scenery in the middle of the room, fixtures across the hall. Ordinary domestic Wi-Fi does not get in the way: these are separate devices on their own radio channel.
RDM (Remote Device Management) is a layer on top of DMX that makes the link two-way: the desk can interrogate fixtures, read the model, check the temperature and — most importantly — set the address and mode remotely, without climbing up to the fixture. It runs over the same cables but needs support from both the fixtures and the interface. It is rare in the budget segment, so this course assumes addresses are set by hand.
Key points
- An interface is the translator between computer and DMX line; it can be USB or network.
- Almost every USB interface needs a driver; an empty device list is nearly always that.
- A universe is one line of 512 channels; add up your rig’s channels in advance.
- More than 512 channels means several interfaces, a multi-port interface or network output.
- Art-Net and sACN carry DMX over a local network; the beginner’s classic mistake is the universe numbering being off by one.
- Network: wired only, one subnet, and the firewall must not get in the way.
- RDM allows remote configuration of fixtures, but is not supported by everything.
Coming next: we are done with hardware. The next lesson is about the words every lighting desk in the world speaks: scene, chase, preset, fade, submaster, blackout, and the mysterious HTP and LTP. Without that vocabulary the interface of any program looks like a riddle.