HTP Preset Boards

[Daveman]

I have a question about the operation of HTP preset boards. I'll try and explain as best I can:

 

Say you have channel one on preset A set to DMX level 200, and channel one on preset B set to DMX level 100. As you pull both the preset masters down to fade out preset A and bring in preset B, the mathematics of scaling would mean that if both preset masters fade at the same speed, the channel level will go down to below DMX level 100 and then rise back up again. Here's a table to illustrate the fade:

 

Percent A Percent B

100 200 0 0

90 180 10 10

80 160 20 20

70 140 30 30

60 120 40 40

50 100 50 50

40 80 60 60 <<<< Value of channel 1 continues to drop below 100.

30 60 70 70 <<<< And now starts to rise back up again.

20 40 80 80

10 20 90 90

0 0 100 100

 

Is this actually what happens on a normal board? I haven't used a huge amount of preset boards but this behaviour would surely be undesirable. I'm trying to build a simple software preset board simulation and when putting in the scaling code the above is the result, however I'm not sure what the error in my approach is, if any!

[themadhippy]

yep thats about it.some boards (sirsus for one ) have dipless crossfade to overcome the problem

[Smiffy]

What feels now like a veeeeeery long time ago, I was taught that to create a dipless crossfade, the out time of the preceeding cue needed to be slightly longer than the in time of the next cue, or it may be the other way round (it's signle digit AM hours here and I have had nowhere near enough Caffeine yet). Anyway, that's the gist of it :)

 

Cheers

 

 

Smiffy

[paulears]

From many years on non-dipless crossfade systems, it's not so much the change in start time, but the profile of the fader movement, as in speed changes - after a bit of practice, you can adjust it to that they pass each other at 6 and a bit.

 

The worst case is when you had a light full on row 1, and the same light on row 2 at the same level - this would be the one that stood out as it dimmed a bit then went back up. With the two handed fader move dipless was quite possible.

[pritch]

ISTR us going into this in huge detail some time back...

 

http://www.blue-room.org.uk/index.php?show...&pid=182779

 

I'm not sure if that thread answers your question?

[Daveman]

Thanks guys that's really helpful! Would also explain a lot of the issues I've had using a preset board before...