DMX output: Art-Net, sACN and USB

Getting light out of LMX and onto the rig.

Nothing leaves the machine until you enable an output. LMX can drive all three at once - Art-Net and sACN over the network, plus a USB DMX interface - and each has its own set of enabled universes.

Everything here is on the Config window (File → Config…) as well as on the command line.

Art-Net

CONFIG ARTNET ENABLE            # or ON
CONFIG ARTNET OFF               # or DISABLE
CONFIG ARTNET BROADCAST <ip>
CONFIG ARTNET UNIVERSE 1 THRU 4 ON
CONFIG ARTNET UNIVERSE 5 OFF
SHOW ARTNET

Art-Net goes out on UDP port 6454. The broadcast address is the one thing worth getting right:

Address	Sends to
`2.255.255.255`	The classic Art-Net `2.x.x.x` network
`10.255.255.255`	A `10.x` network
`192.168.1.255`	That subnet only
A specific node’s IP	Just that node (unicast)

A broadcast address that does not match the subnet your interface is on is the usual reason “Art-Net is on but nothing moves”.

Remote visualiser

CONFIG ARTNET VIEWER <ip>|OFF

sends the output to a visualiser on another machine, independently of whether the rig is being driven.

sACN (E1.31)

CONFIG SACN ENABLE
CONFIG SACN OFF
CONFIG SACN [IP <addr>] [PRIORITY <1-200>]
CONFIG SACN UNIVERSE 1 THRU 4 ON
SHOW SACN

sACN uses multicast by default - one multicast group per universe, which is usually what you want, because nodes subscribe to the universes they care about and nothing else sees the traffic. Setting IP switches to unicast at that address.

Priority (1–200, default 100) is how sACN arbitrates between two sources on the same universe: the higher priority wins. Raise it if a second console or a node’s own default output is fighting you.

USB DMX

LIST USB                        # what is plugged in
LIST PORTS                      # serial ports
CONFIG USB DMX UNIVERSE 1 DEVICE <usb-id> [FPS <n>] [MARGIN <ms>]
CONFIG USB DMX UNIVERSE 1 PORT <serial-port> [FPS <n>] [MARGIN <ms>]
CONFIG USB DMX OFF
SHOW USB

Name the interface either by its USB id or by the serial port it presents. FPS sets the refresh rate for that interface and MARGIN the inter-frame gap in milliseconds - worth increasing if a long or noisy DMX line drops frames.

Frame rate and priority

CONFIG FPS 40                   # output frame rate
CONFIG PRIORITY HIGH|NORMAL     # process priority

CONFIG PRIORITY HIGH asks the operating system to favour LMX, which smooths output on a busy machine.

Checking it is working

SHOW OUTPUT                     # the merged output
SHOW ARTNET / SHOW SACN / SHOW USB
DUMPDMX 1                       # every channel of universe 1, as sent
SHOW PERFMON                    # frame timings

The status line along the bottom of the main window shows live frame rates per protocol: AN: Art-Net, sACN:, USB:.

When there is no light

Work down this list - it is ordered by how often each one is the answer.

Is anything actually on? SHOW PROGRAMMER, and check the grand master is not at zero.
Blackout or Emergency? Both toolbar buttons light up when active.
Is the output enabled at all? SHOW ARTNET / SHOW SACN / SHOW USB.
Is the universe enabled? A protocol can be on with that universe disabled.
Is the fixture patched where you think? PATCH REPORT.
Right network? Wrong broadcast address, or the machine is on Wi-Fi while the node is on the wired interface.
Is something else winning? On sACN, a higher-priority source takes the universe.

INSPECT FIXTURE <id> prints the whole stack for one fixture and says which layer won - it answers “why is this lamp doing that” faster than anything else.