My lightshow doesn’t play back accurately, and some events don’t play at all

The problem – bad timing

You have programmed some fast changes into your DMX light show, for example to follow the beat of a song. But your lights seem to react sluggishly, and sometimes the lights seem to skip a beat.

The bottom line

The DMX protocol is not designed to handle very fast lighting changes, and you cannot make your lighting rig strobe accurately at high speeds (e.g. 16th notes @ 120bpm).

The detailed explanation

The DMX protocol allows for updating your lights at a maximum of 40Hz – that’s one update every 25ms. However, because many lights struggle to cope with the 40Hz rate, some controllers (including DMXIS) deliberately throttle the update rate to 25Hz, or one update every 40ms. This means you will run into timing anomalies quite easily if you try to program fast strobes.

A little math is required to explain further. Say you want your lights to flash on every beat of a 120bpm song. Each beat lasts 60/120 = 500ms, so to flash the lights on/off requires a DMX event sent every 250ms. This is much higher than the 40ms update rate, so all looks good…

Now, say you want to flash on every 1/2 beat. This needs a DMX event every 250/2 = 125ms. This is higher than the 40ms update rate, so every update will be received by your lights. But, you will start to notice some timing inaccuracies in the strobe effect…

Now, let’s go to 1/8 beat strobing. This needs a DMX event every 62.5/2 = 31.25ms. So now we’re in trouble – not only will the lights be unable to accurately track your desired pattern, but you will actually drop some events because the DMX hardware simply cannot keep up with the changes…

Unfortunately, the DMX protocol simply doesn’t handle fast changes well. If you want to strobe quickly, use the “strobe” macro feature that is built into most DMX lights. While they may not strobe perfectly in sync, they will at least strobe at a consistent rate.