DMX512 is a Digital MultipleX of data values, most commonly used for lighting and related control in live performances, video studios and theatre.
Why DMX?
In a world where we have so many standards, DMX is one of the few universally accepted protocols, appearing on fixtures and control systems used in any professional lighting application. Of course, there are some variations in pinouts/connectors (despite the standard) and the quality of the decoders can vary.
DMX is mostly commonly used for dimming, but in live shows is also used for colour, position, and other effect control. Once upon a time, a large rack of DMX-controlled dimmer racks would be hidden off-stage, but with the move to smart fixtures and LED, most lights have DMX control on-board.
For all the gory details, Wikipedia has a good backgrounder, and there are many good reference sites.
DMX in a corporate video studio
For corporate video, it is tempting to skip lighting control and just use standard office light wiring, or a building control system like C-BUS or DALI. This will often work OK, but it means setting dimmer values at the fixture rather and having no control other than on/off. This means and adjustments have to be made at the fixture, which may involve step ladders and safety concerns if staff aren’t experienced.
If you are using a green screen, or a changing environment like a radio studio, we recommend going with a DMX system. The investment is surprisingly small and you will get a lot more control and flexibility. Precise dimming control helps balance the lighting levels in your studio, and we can’t stress enough how useful this if for green-screen work.
Most fixtures designed for studio lighting will include a DMX option, and many include it as standard. You just need to make sure the fixture will actually dim smoothly, particularly if you plan any lighting changes during live work.
Hardware to talk DMX is very cost-effective, and if your needs are simple the software is free. Read on for our DMX tips.
How OnAir Solutions tackled DMX
When we built our own demo green-screen TriCaster studio in our Sydney showroom, we wanted to include DMX to show easy it can be.
We started with the Jands JLX-Lite lighting bar. Available in white, black and custom colours – the JLX-Lite comes in 1600mm and 2400mm lengths. It includes 4 or 6 Australian/NZ mains sockets and space to install DMX chassis connectors. We have two bars and wired the DMX in a daisy-chain to each, because our needs are pretty simple.
We then added the ENTTEC ODE Mk2 Ethernet DMX gateway. This connects on your network, powered by PoE, and provides a high-quality DMX output.
Finally, you need some software. We’re assuming that for corporate video you don’t want or need a hardware lighting console. If you do, there is ample choice from budget to high-end. But for us, a simple software solution was all we needed.
The good news is QLC+ is available for Windows, Mac & Linux (inc Raspberry Pi) for free. It’s pretty simple to setup and is well-documented. Its actually pretty powerful software and is widely used.
Troubleshooting
Like any communication protocol, there will be times DMX doesn’t behave like you expect. Common problems are no communication, address clashes and flickering lights.
There’s countless tutorials you can find, but here’s our hit-list of things to check:
- Cable – you need to use suitable cable, not mic or analogue audio cable. We often use Belden 1800B, it’s great for AES audio, Analog Audio and DMX, and means we don’t have to keep as many types of cable in stock. It needs to be a twisted-pair for noise rejection, and the right impedance, especially for the longer runs.
- Earthing – like with audio, earth loops can sometimes be an issue. Best pratice is to earth the cable drain wire at one end only (eg the DMX origin point), and lift the earth at the other end. Unlike audio, this can be harder to manage as your daisy-chain cables would normally carry the earth through. So its probably best to ask for advice before doing this.
- Connectors – any compliant fixture should have a 5-pin XLR for DMX. But because DMX normally only uses a balanced data pair plus signal ground, it is still common to see 3-pin XLRs used. In a fixed install it is easy to standardise, but in the field you normally need some adaptors handy. Make sure pin 2 goes to 2 and 3 to 3. A swap between 2 and 3 somewhere in your chain will definitely cause problems.
- Termination – as DMX is a transmission line, it needs termination at the end. This is usually a 5-pin XLR with a 120ohm resistor. Some fixtures will do this with a switch, and some claim to do it automatically. Our advice is find out, and be ready to put a DMX terminator on the end of the line. It helps stop reflections in the signal, and becomes very important in a long chain or with a lot of DMX data (many fixtures).
We recently had to troubleshoot a DMX install used in a landscape lighting installation. Because one cable had to run in a conduit near a power conduit, the system was picking up noise and flickering once many simultaneous lights were on. We also suspect some of the garden LED dimmers and directly controlled fixtures weren’t playing nicely. This is common in the DMX world, so you sometimes need to play around to find a solution. The combination of lifting the signal earth one end, and an ENTTEC D-Split for isolation got the system fully stable.
Find out more
If you’re building a corporate video studio or need assistance with DMX solutions, please get in touch with us at OnAir Solutions. We have the full ENTTEC catalogue available on our webstore, with some items, in Sydney stock.
We can also assist with any of the Jands catalogue of lighting equipment, including lighting bars, control consoles and fixtures. If you’d like to see it all in operation, email us to book a time in our demo green-screen studio in Sydney… we’d be happy to show you through it all.