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Digital multiplex (DMX) channels are individual streams of data that run through a single line of communication to control a variety of devices. They are famously used in lighting control, particularly in the case of the DMX512 protocol; the “512” stands for the number of channels available for use. Although 512 channels might sound like a lot, professional stage lighting for events such as rock concerts can actually require multiple DMX master devices to fully control all of the lighting and special effects.
Each DMX channel can convey information from a control panel such as a lighting board. The DMX channel controls are sometimes known as “dimmers” and might be referenced by dimmer number. The operator can set every channel to a value between 1 and 255. At 1, the channel has no output, and the device controlled by that channel should be off. When the channel is at 255, it is at maximum power; in the case of a light bulb, it would be fully illuminated.
Devices listen in on their own DMX channels and adjust in response to the controller's operation of the board. Some controls can be automated, allowing an operator to enter a pre-set program. This can be useful for complex lighting and special effects with which it might not be physically possible to control all of the lights at the same time. Lighting for a show might be largely able to run itself after being programmed, although an operator still needs to be present in case of an emergency.
Operators can reassign DMX channels to different devices as needed. On a large set, some devices might not be assigned to a channel because they are not in use, but they can be reassigned later when a lighting designer wants to use them. It also is possible to assign multiple DMX channels to a single instrument or device, which is why 512 channels might not meet the need for a production. One device could easily use five or more channels.
Stage lights, in addition to having bulbs that brighten and dim, might have special features that need to be controlled separately. DMX channels can be used to change the focus of the light, add gobos and other effects, rotate gels to change the light color and add icing effects to make the light seem softer and more blurry. The light board operator needs to be able to manage all of these settings individually through their own DMX channels.
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