Control
Being able to turn lanterns on at the correct brightness and at the correct time, is just as important as hanging and pointing them correctly. From the early days of mechanical dimmers, control systems have developed with increased sophistication and cost!
Manual Desks
'Manual' desks consist of (usually) two sets of faders, with each set containing a fader for each channel of control. Each of these sets, (often labelled A and B) have their own individual master which governs the output levels of all faders in that set. Masters can only reduce the levels fed into them, i.e. they never increase the values.
E.g.
TODO *** JAVA applet/DIAGRAM
A C1 C2 C3 C4 MA -> output
B C1 C2 C3 C4 MB
A C1 C2 C3 C4 MA -> output
B C1 C2 C3 C4 MB
A C1 C2 C3 C4 MA -> output
B C1 C2 C3 C4 MB
Cross Fading
With this arrangement of masters it is possible to fade between the two sets, to transition between two different lighting states. This saves having to employ an octopus as the board operator—as multiple channels can be faded in or out simultaneously with just one fader. Furthermore most A/B masters operate in opposite directions (e.g. Master A is 100% at the top and Master B is at 100% at the bottom) which allows both faders to be moved up or down in parallel to cross fade (i.e. fade one out and the other in simultaneously). Obviously it is also possible to move A and B separately to fade both sets out (to fade to blackout) or fade both in together to combine.
Combining Sets
When sets combine they do so as Highest Takes Priority (HTP) – meaning that from a choice of competing values for a channel, the highest is used. HTP is nearly always used for control of the intensity of fixtures, though desks used with moving fixtures usually adopt Latest Takes Priority (LTP) to control position and other attributes.
TODO DIAGRAM
TODO PHOTOS of all the bits on a desk
Timer Functions
The slightly more sophisticated manual desks have a timer function, which enables fade times to be set for the A/B masters. The time it takes for the master to fade to any new value is determined by the value of the timer, with a time of 0 specifying manual control. e.g. with the time set to 10 seconds, if a master is quickly moved from 0% to 100%, the actual output will fade smoothly from 0% to 100% over a time of 10 seconds.
Grand Master
The Grand Master (GM) is the final master fader and affects whatever is being output from the desk. E.g. if the Grand Master is set to 0%, then there will be no output from the desk, no matter what the other settings are. Similarly there is often a Blackout switch (sometimes labelled DBO) which literally does what it says – sets the output of all channels as 0%, giving a blackout!
Checking the masters (and that their actual physical position corresponds to their actual value, and not that a very slow fade is happening) and the state of the DBO are often the first steps when determining why channels are apparently not turning lanterns on. Memory Desks
Memory desks are able to store sets of channel values and then play them back when requested which is a big advantage over manual desks.
There is an enormous range of memory desks available, offering a wide variety of features and each differing in exact details of operation. Consequently this guide does not go into specifics and instead covers the common principle and concepts. All the major manufacturers have their manuals available from their websites, and in many cases an off-line simulator for a PC.
Desks used for theatre tend to make use of a "Cue Stack" or a bank of "Submasters". In both cases a lighting 'state' (a set of values for every channel) is recorded so that it may be played back later. The cue stack defines the order the states come in, and how to transition (e.g. fade) between them. Submasters allow a state to be faded in and out by hand (rather like an A/B master fades in and out all the channels in a set) and combine as HTP. For each state the timings of a range of parameters are adjustable, including for each state:
- The time taken to fade the new state's lights in
- The time taken to fade the last state's lights out
- Optionally the time before automatically progressing to the next state
- Optionally the next state to follow (to allow looping through states)
More sophisticated desks have pattern generators and facilities for recording chases. Pattern generators are used in the control of moving lights; parameters are specified, such as the shape e.g. figure of eight, oval, triangle etc. the speed, size, rotation, position, etc. instead of recording the exact position all along a complex path. Patterns and chase sequences may be linked into cues or submasters to control when they start and stop.
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