uDMX demystified (at last)

[GGGss]

Since many users are going for the buck, they all bought cheap DMX interfaces and reported flickering to the forum. After all, you get what you pay for.
So, to reflect on forum responsiveness, I bought a uDMX adapter to see and measure for myself what is going on.

Test setup: QLC+ latest on a Windows laptop, uDMX USB to DMX converter, 2 static lights (A1 and A408), and my beloved DMXCat measuring device.

Out of the box (clean install, no fancy pancy, ...) plug the uDMX into a USB port. (no drivers whatsoever) - the device manager detected the USB FTDi device with COM3. Defaults to 9600bps (**) For what it's worth**.

Start QLC+, and a clean output device is ready to be used.

When composing a simple project in QLC+, I instantly noticed flickering with the fixtures. Opening my DMXCat application, I saw what was wrong:

In QLC+, configuring (out of the box) the interface to 30Hz DMX bus speed, overkilled the DMX interface, resulting in a (poor) 10Hz-ish refresh rate. Albeit QLC+ reports 'good' conditions -> It Is NOT!

The following post will show what is reasonably feasible with the uDMX interface. Remember: It IS a slow device (!)

[GGGss]

So, What is feasible?

The definition of flickering: An interface which can not cope with the info given results in these hiccups:

If it comes to "what is clearly visual", it comes down to dimming curves. If one would create a theatre production where the dim-down would be in five steps - he'd be thrown onto the barbeque.
Now, here is where DMX bus refresh rates come into play.
A typical dim-down (fade time) of two seconds works best. If you have a DMX bus frequency of 10Hz (see above post), you (or the trained eye) will notice the steps in the fade curve.
The dimming curve will be a 2000 ms / 10Hz = 200 steps - unnoticeable!

Under these conditions, the best performance can be achieved by lowering the DMX bus frequency using the uDMX interface.
My measured threshold is at about a QLC+ setting of 16Hz which will result in a measured full 512 channel @9Hz DMX bus frequency.

Important notice: These conditions are measured with my laptop. Dell XPS17 (Intel(R) Core(TM) i9-9980HK CPU @ 2.40GHz 2.40 GHz, 16GB Ram) and a dedicated GPU. <- This is not the average computer in space...

(I pushed the settings too hard - look for the red break times)

Note: @massimo, the registry uDMX entries did not alter my findings. Should the documentation be updated?

[mcallegari]

I just checked and the registry keys should still be consistent with the documentation:
https://github.com/mcallegari/qlcplus/b ... ce.cpp#L41