DMX/ Noise interference?

[Charlihurford]

 

I've got some DTS bricks that flash out of their normal state erratically into  purple throughout performances. Still gathering information on how regular, but it does seem to occur with loud noises (but not every loud noise)- Only a couple times and slips back into it's programmed state. I've checked all the DMX cables to make sure they've not been a snack for a squirrel, but all looks to be in order. Has anyone had a similar issue with these or any similar lights? 

Thank you!

[DrV]

Have a look at this thread. You may be seeing the same problem. As for the association with loud noises, that may just coincidence - we humans are slaves to our desire to find patterns in things!

[Robin D]

Do the devices have a sound to light function? If so it may be triggering. I can switch some of mine into sound to light mode with an appropriate DMX signal. 

If they do have sound to light, find the microphone and cover it with a pad of something to absorb the sound. See if the problem goes away. However it will not help if vibration is coming up through the fixture mechanically, in which case try to decouple it from whatever is vibrating. 

 

[DrV]

Just had a quick search of the manual and there's no mention of "sound" or "audio" anywhere. Moreover the fixture does support setting things via RDM so it's clearly not the same issue as described in that other thread that I linked to. Sorry about the red herring. What desk are you using?

Edit: Also, what other fixtures have you got on that DMX line and is it terminated correctly?

Edited September 22, 2023 by DrV

[Tomo]

Broken cable can do this kind of thing. DMX (like most digital protocols) tends to keep working reasonably well under absolutely terrible conditions - until it suddenly doesn't.

DMX is perhaps worse than most, because there's no error checking and error correction is entirely based on the idea that a new packet will be along in a few milliseconds to correct a wrong value. That worked very well with tungsten lamps and (to some extent) moving lights because they simply can't physically react that fast - but LEDs can.

Making sure your cables are correctly terminated both prevents a lot of issues and - perhaps more importantly - causes a semi-broken line to stop working altogether, instead of intermittently doing crazy things. Much easier to find and fix the problem.

I've seen many sites where one of the wires had broken and was making intermittent connection. It'd usually appear to be just fine, then occasionally cause all kinds of weird flicker - sometimes apparently triggered by loud sounds, possibly because the noise would make the broken strands vibrate.

[niclights]

If your console has an option you could try enabling extra stop bit.  In my experience this has solved flicker issues on certain fixtures.  Although if it really is occuring with sound then that suggests either sound to light or something physical.

[timsabre]

Is there an induction loop in the venue? I have seen a similar thing where a DMX system with a broken wire (I think Data+ was connected but not Data-) worked most of the time but audio on the induction loop would make it fail.