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[Scotty Myers]

I've just "inherited" a few lighting install jobs after the previous guy left a facility hanging a week before opening.  I'm a 58 year old acoustic engineer and have always left the "trivialities" of lighting to someone else, snubbing my nose up.  But I figured, it might be interesting.  I got the facility up and going and they are happy, but I need to now really wrap my head around DMX control and controllers.  I'll start with DMX channels first.  (I was around for analog light control and saw the advent of AMX.)

So what I first want to "get" is how the channels on fixtures work and I don't think I can truly tweak a system to its Nth degree without this understanding and I'm not sure where to read on this.  I've stumbled around figured out some things on a software controlled system.  Take for example a basic RGB fixture; so that's simply three channels.  I can control color with those three channels and I can dim and change color by sending out how much of any color I want.  But if I want to "limit" that fixture's brightness "under the hood" so a client can't easily override it, I need a fourth dimmer channel and can limit brightness by setting it's maximum to something lower than the maximum 255 value.  There may be other ways to do this, but this is how I chose recently.

On another fixture that I had zero documentation to and was too old to find it, I had to stumble until I figured out which channels worked for RGB, which was dimmer, which was shutter, etc.  It didn't take too long, but still a pain.  It was able to be set to up to 12 channels, but I didn't need all of them and didn't know what they all were.  The dimmer on this particular fixture seemed to be channel 1 and the colors 2,3 and 4.  But perhaps I need to more thorough understanding of DMX channels on a fixture to "get it".

So what I'm trying to find out are the subtleties of DMX channels and interactions.  I feel like I'm shooting in the dark.  This seems to vary by fixture manufacturer.  I'm simply not sure where to look for the information.

[Taylor Hall]

You've basically grasped the core concept of channels in your experimenting. A channel is assigned to a single function of a fixture such as individual color intensity, pan/tilt (for movers), master intensity, effects/strobe, and so on. Having documentation for the fixtures you're using will let you know exactly what these various channels will do. One important thing is that channels cannot overlap. For instance, you have a fixture that uses 5 channels and it's set up to start at channel 1 (so it occupies channels 1-5). Even if you're only utilizing the first three channels for that fixture (say for simple R/G/B manipulation) you can't set your next fixture in the chain to start at channel 4, otherwise it will get sent the same data as the first fixture, but in the wrong channel. So you could be sending strobe or master intensity commands without any color! What you CAN do is have multiple fixtures set to the SAME channel range. So if you wanted multiple fixtures doing the same thing at all times, just set them all to the same channel and you don't have to duplicate scenes many times over. The only caveat being that you'll need to go back and set them to unique channel ranges if you ever need that additional customization.

With newer fixtures they can be set up in different channel modes. For instance, a standard par can have a 3, 5 or 7 channel mode (some movers can go well over 20 channels!). In the 3ch mode, you could only be controlling the R, G and B channels. In 5ch you get R/G/B, master intensity and strobe and in 7ch you get a couple extra features (note these are just examples, different fixtures have different mode setups so having documentation is key in this regard). Additionally, channel functions can vary between manufacturers and even models (as you've found), so you could have your work cut out if there's no manuals for anything.

For channel modes, you want to have the smallest number of channels in use as possible while still getting all the functions you require so that you're not eating up your universe. A DMX universe is limited to 512 channels, so if you have a dozen or so fixtures in 7ch mode you're already eating up nearly 100 channels. If you trim those down to 3 or 5ch mode, you'll have much more room to expand (as well as declutter a physical desk with unused channels).

For your "limiting" scenario, I would check first if the fixture has other channel modes as mentioned above. Then, you should be able to set an artificial limit through your lighting desk or software solution. You may have to be tricky in your software depending on how much you can edit. Some will allow you to do this in the main show file, but others may require modifying the fixture definition itself, so proceed with caution.

If you have the make/model of the fixtures you can't find manuals for, we might be able to help out locating them.

[Scotty Myers]

Thanks Taylor.  I have indeed figured all that out you mentioned and explained, but always good to have it reinforced.  I am feeling validated!  LOL  As you mentioned, the one thing I am grumbling about now is the number of channels I set each fixture to in this facility.  Back when I accepted this challenge, the owner of the facility told me he wanted all options open on each fixture, which meant maximum channels.  At that point, I did't know what I didn't know.  In retrospect, they will NEVER use all those channel features... ever.  So now universe 1 is pretty busy and I'm sure when I install the next set-of moving heads and what not, I'm going to have to roll the lift all over the room (25' in the air) and reset the maximum channels on each fixture and then reset them in the software.  A royal PITA.  Some of the LED pars are 12 channels and he's got 20+ of them! What a waste of channels.  He'll never know that they are not set to maximum channels, nor will he care in the end.  He likes the look now and I'm only using maybe half the channels on any given fixture at this point.

>"For your "limiting" scenario, I would check first if the fixture has other channel modes as mentioned above. Then, you should be able to set an artificial limit through your lighting desk or software solution. You may have to be tricky in your software depending on how much you can edit. Some will allow you to do this in the main show file, but others may require modifying the fixture definition itself, so proceed with caution."

That's where one of the first "rub" came in.  They had chosen Lightkey (I ask about this in another thread) and it seems there is no way to control maximum intensity on a fixture without modifying the fixture definition in Lightkey.  That was easy enough since I simply used that 4th dimmer channel in the definition and set a maximum range of 0-50, instead of 255.  Problem solved.  I'm sure other hardware/software can limit the maximum without modding the definition but it doesn't seem that the current rendition of Lightkey can do this.  Not a big deal at this point.

[Taylor Hall]

That's where one of the first "rub" came in.  They had chosen Lightkey (I ask about this in another thread) and it seems there is no way to control maximum intensity on a fixture without modifying the fixture definition in Lightkey.  That was easy enough since I simply used that 4th dimmer channel in the definition and set a maximum range of 0-50, instead of 255.  Problem solved.  I'm sure other hardware/software can limit the maximum without modding the definition but it doesn't seem that the current rendition of Lightkey can do this.  Not a big deal at this point.

I haven't messed with LightKey that much, but does it have the ability to configure a slider/button as a submaster? Another software solution I've used has this function and it basically allows you to impart a master intensity type effect to whatever scenes it is applied to. A quick google search didn't show anything by that exact name in lightkey, so they may call it something else. That way you could only give them the ability to go as high as the maximum value of the submaster without modifying the fixture definition.
You can see it in action here about 40 seconds in: https://www.youtube.com/watch?v=0Sp-dlTLpe4

[Scotty Myers]

>"I haven't messed with LightKey that much, but does it have the ability to configure a slider/button as a submaster?"

Taylor,

I'm not sure honesty, but I think the answer is no.  Lightkey is a much simpler solution keeping control simpler, but with that comes a certainly loss of control flexibility.  As I work with it, I may find a way to do it such a thing.  I'm going to ask them.  I see what you mean in the video.  That is exactly the kind of thing I was looking to find that doesn't seem available in Lightkey.

In this specific case, I had 4 fixtures that needed controlled with one slider.  2 of them need to be able to vary from perhaps 30% to near full brightness as they are 22 feet from the lit subject, while the other two had to be limited at much lower levels as they are being used as footlights and are very close to the lit subject.  There isn't a way assign one submaster to series to two other submasters that are set at a lower levels to allow such "ratio-ing" that I can find within Lightkey.  So I grouped the 4 fixtures, assigned them to a slider and then modded the definition of the two than always needed to be ratioed at a lower output level.  It worked.  Not sexy and seriously lacks flexibility though, as there is no way to easily override that low level.

[Taylor Hall]

If it has that limitation then you could check out QLC+ which is what is shown in that video. Free to use and pretty powerful. It might take some re-learning if you wanted to convert everything over, but might be worth exploring if you have any free time.

[John L Nobile]

I'm an audio guy forced to do lighting as well. It was giving me a headache. I wound up hiring a real lighting designer and had him focus and program the rig. No more headaches and I get compliments on the lights.

[Jeff Lelko]

So what I'm trying to find out are the subtleties of DMX channels and interactions.  I feel like I'm shooting in the dark.  This seems to vary by fixture manufacturer.  I'm simply not sure where to look for the information.

Yes, it varies by make/model of every light.  There is no standard for attribute assignment.  The best place to find the DMX channel assignments is in the unit's manual, which should be available on the manufacturer's website.  If this isn't available, you can try a trial-and-error approach, but that's about the best you can do at that point. 

Regarding channel interaction, it again will vary.  Many complex fixtures have certain channels that override other channels or put the unit into a different operating mode.  I'll use the Elation Sniper Pro as an example since I have my inventory out for programming today...  It's a 27 channel fixture.  Some of these channels will always stay "independent", in that things like the fixture's Cyan, Magenta, and Yellow attributes on channels 9, 10, and 11 will always be controllable no matter what the rest of the unit is doing (short of resetting it via a command sent on channel 27).  Other attributes aren't so simple.  I can pan and tilt the unit via channels 1-4, though the absolute position of the beam will be overridden by "shake" commands sent via channels 5-8.  Even then, those will be overridden by a pattern macro sent on channel 17 if it's at anything other than a nonzero value...  It takes practice to learn to program fixtures like this quickly. 

Oftentimes your console or controller can take a lot of the guesswork out of things.  Aside from having preprogrammed device profiles, they can also work wonders for color mixing.  Instead of figuring out the right amounts of RGBAW to add to make a certain color, I can just click on
a color or drag my cursor around a color wheel and let the board work its magic to output the appropriate result.  It just depends...  This is why I don't disagree with John's response - once you reach a certain point of complexity it pays to leverage the experience and skill of a real LD to get things done in a timely and professional manner.  Hope this helps!

[Scotty Myers]

... There is no standard for attribute assignment...  Regarding channel interaction, it again will vary... 

Excellent response and explanation of the "lack of channel standards" and how certain channels seem to "Take over".  That explains a lot.  Thank you for taking the time.

Scotty

[ProSoundWeb Community]