Show Control is a term widely used to describe the set of devices that controls and synchronizes the various elements of an attraction. Henry Corrado, Director of Tejix s.a.r.l, explains the artistic, financial and operating aspects of designing a great show control system.
Show Control is a hub of elements as diverse as image projection systems, physical effects, water, flames, lasers, pistons and any other element that springs to creative designers’ minds. Show Control engineers must be able to understand these different disciplines, and possess both artistic sensibility and knowledge on ways to syncing mechanisms. This short article aims to familiarize readers with the bases of this discipline.
Related: Sound Advice from Leading Lights: The Future for Audiovisual in the Attractions Business / Making (Audiovisual) Waves at Disney / Aspects of EXPO 2010 -an Audiovisual Review / Audiovisual technology: A short history of the videowall / Tejix Company Profile
Matter of time
The most obvious function of the Show Control system is that of controlling the show elements: triggering effects at exactly the right time during the show. We will see later that this is the tip of the iceberg. This syncing function differentiates the Show Controllers used in attractions from those that operate industrial plants and bottling facilities. The main difference between these two worlds is the ability to trigger an event at a very specific moment. This raises the question of the time unit used, and the acceptable tolerance.
The single answer to these two questions has a unique historical origin: the movies’ rate of 24 frames per second was chosen because it is higher than the persistence of vision, the period during which the images we see are "printed" on our retina, (this is not entirely true, but we accept this assumption for the purpose of this article). Since an attraction is composed of visual elements, often films and video images, it is reasonable to accept as adequate the temporal resolution of the human visual system. For convenience, the unit of measure normally used in a Show Control system is the "frame".
Specifically, the images are counted from the beginning of the show. When an effect must be triggered at a particular time, its frame number is used. In practice, the time code standard used is the one defined in the early days of cinema by the Society of Motion Picture and Television Engineers, and adopted by the European Broadcasting Union, among others. This code is so common that it took the name of the organization that created it: SMPTE. In the SMPTE time code, each frame is described not by number but by its position in time, in hours, minutes, seconds and frames. Several rates are used, each corresponding to a specific use or world region (24 frames per second for film, 25 for video in Europe, 29.97 or 30 for video in the U.S…)
All the elements of a show will run at the same rate, most often 30 frames per second in theme parks.
With the "SMPTE" time-code, it is possible to close the doors of an attraction at 01 hour, 2 minutes, 5 seconds and 14 frames. This does not mean that the show lasts for several hours: it is customary that the time "0" of the show matches the time-code value 1:00 hour. This allows the use of “negative" time called "preroll" to set elements that require preparation time, such as mechanical effects.
The SMPTE time-code of an attraction can have several origins depending on the system design: a film projector, a video, a sound track.
The most professional approach is the use of a separate generator, an independent device whose accuracy and performance qualities are known. Time code is often distributed to sub-systems used in the attraction: audio, video, special effects, lighting and animations are all listening to the same clock.
To ensure perfect accuracy, in particular to ensure that the transition between images occurs simultaneously in all devices, a video synchronization signal is often distributed in the form of what we call "video sync". This is a series of bursts indicating the end of each line and each frame of the video image.
Besides triggering events at the right time, another function of the control system is to control …in a logical sense.
This function is so close to that of an industrial controller that they are sometimes used as subsystems in attractions. In most cases, logical functions are performed by the main Show Controller, whose mixed time/logic approach makes more sense for the designer and the programmer.
In a simple world, an attraction would be conducted in the same manner as a film, and it would be possible to move at will from one place to another in the show with a mouse click. While this is theoretically possible, this power is limited by the nature of the elements that are controlled: for example, physical effects can not instantly find their position, and animatronics resent abrupt changes.
Moreover, show elements are triggered on a time basis, but only if specific conditions are met. Those conditions are sometimes hierarchical. The purpose of this is mainly to ensure the safety of persons and equipments, and maintain show integrity. Thus, before triggering a rain effect it is wise to ensure the presence of water, pump status and the fact that the show is actually running. In practice, these checks occur within seconds or a few frames before the effect itself. What seems very fluid in the course of the show is in fact a "program block" which includes logical operators and a time-code trigger.
Technical interaction between the operator and the attraction is often limited to the console operator, "OCC" for Operator Control Console in the parks jargon.
This interface must be simple and contain a minimum amount of controls and indicators. Most often, OCC includes just a start and emergency stop button. If the attraction is equipped with automatic doors, these can be controlled manually from the OCC. Lights often indicate the show status and possible faults.
This rustic approach of an OCC with big industrial buttons is simple and reliable. Sometimes, however, more detailed information should be brought to the attention of the operator (keeping in mind that the operator is not a technician). In this case, a screen can be added to the control interface.
While the idea of a touch-screen control interface is attractive for its flexibility, the solution is rarely used because it lacks reliability. Never forget that, in the vast majority of cases, only a few functions are needed on the OCC, and limiting the potential sources of failures is crucial. Even if this is not directly related to Show Control, the OCC often includes means of communication: a microphone to make announcements to the guests and a telephone or an intercom system that allows contact with other locations in the building, such as the preshow, technical room, queue line, etc.
Except in the smaller projects, the Show Control system consists of not just one device, but a set of systems that work together. There is no universal design adaptable to all situations, but as many approaches as there are designers and projects. When designing a system, the first thing to consider is the devices to control and their physical location. This will help determine which element will hold the central role in the system. It is also possible that the system is fully distributed and no device is really a "master".
In a typical attraction, a main Show Controller (the "Master Control Show") provides the overall control. This master communicates to all subsystems, such as audio-video, lighting, animation (animatronics, figures), special effects … This "block" approach allows more flexibility in programming, operation and maintenance of the attraction. Each subsystem is designed according to the canons of its discipline. For example, a specialist in physical effects legitimately swears only by PLCs, which are obscure for a lighting designer.
The Master Show Controller, in addition to synchronizing the various components, communicates with the subsystems on the operating conditions of the attraction. The decision to stop the show in progress, or to prevent restart once it's over, is taken by the Master Show Controller after a subsystem has reported a fault. Often, the program includes a "matrix of faults" which defines the conditions of the accumulation of defects beyond which the show should be discontinued.
One aspect invariably excluded from Show Control is that relating to safety. This generally includes physical effects such as moving objects, the fluid-based effects and of course ride control. These functions are handled by a PLC. The Show Control system triggers events programmed in the PLC, but the latter is always responsible for safety conditions. Conversely, the PLC communicates to the Show Controller defects and errors, as we saw earlier. The elements of the show, as one might expect, are connected most of the time by electrical wires. These cables are used to convey a variety of different control signals.
Addressing this item without getting into abstruse technical details is not easy. To turn a device on or off, the simplest way is to use a single electric wire to convey "On" or "Off" information (as in turning a lamp on or off). This scheme has the merit of simplicity, but as one wire is used for each item of information, it is very likely that a large number of wires will be needed for a complete show. To simplify wiring, "On" and "Off" information can be encoded in a predefined arrangement.
If the transmitter and receiver have agreed on a common language and communications protocol, they will be able to exchange complex information on a single wire, such as in Morse code, for example.
This is what is called serial communication, as opposed to parallel communication described earlier. By using faster speeds and complex communications schemes, elaborate messages can be sent on what we commonly call a "serial port", such as the ones that were used on computers for mice and printers. Although somewhat dated, serial ports are still used for point-to point where they are appreciated for their simplicity and reliability.
The next step is to pool information from multiple transmitters and receivers on the same wire. In this case, sender and recipient information are added to the transmitted data. The most common incarnation of this is the network adapter on your computer that allows you to send specific messages to almost whoever you want.
Although most communication protocols now tend to move towards the use of networks, Show Control systems regularly use industry-specific communication standards, in addition to the more or less exotic ones used by PLC manufacturers.
Among those are DMX and MIDI. DMX (whose real name is DMX 512) is a solid one-way communication protocol designed to control stage lighting and MIDI was originally designed for electronic musical instruments. These protocols have in common their stability and relative simplicity. They also have been designed to be used by creative people, such as lighting designers and musicians. This is why they are often used to control motion platforms, animatronics, lasers and other devices.
On-site programming is the fun part of the work, although far from the glamorous idea that parks aficionados may have of it. A big part of the programming work consists of defining the script backbone, GUI, conditions… This part of the job does not occur in the attraction itself, but more often at the hotel or at the airport. The real reason why passengers are asked to arrive two hours before their flight at the airport is to allow Show Control programmers to work in normal conditions, in the airline lounge, in front a glass of champagne.
Once on site, the next step is to make sure that all devices communicate. This is normally the time of massive hardware and software debugging where device firmware (and sometimes the devices themselves) are replaced. Once this is done, the media quest can start.
Whatever the size of the project, it seems that there is an unspoken universal rule among media producers only to deliver sounds and images a few hours before the opening of the attraction, at the same time carpet is glued and scaffolding dismantled. Then the few remaining hours are used to give life to the attraction. In an ideal world, or in large parks, it is possible to test the attraction dozens of times before starting a pre-opening. In real life, the first visitors are used as guinea pigs while the show programmer makes final adjustments. They just don't know it.
Programming is really over when all emergency and fault conditions have been tested and validated, and that operators and technicians have been trained. The training phase is crucial: it allows the park to be autonomous and to minimize downtime, so the programmer can enjoy a quiet weekend … to program another attraction.
Ideally, a Show Control system is completely static, ie it contains no moving parts to wear out. Logically, therefore, a well-designed system should not need heavy maintenance, and it should last as long as the attraction itself. There are exceptions, however. In the best cases, the concept of attraction is so good that it will outlive several generations of industrial controllers.
More commonly, inexperienced designers throw the cat among the pigeons by using computers. Although this approach is not fundamentally questionable in technical terms, it is based on the use of short life cycle operating system (such as Windows, for example). When using a computer as a Show Controller, the attraction owner is dependent on new releases and changes of the operating system. In the fast changing world of computers, new hardware will soon be required to match the new operating system. This endless loop makes the ownership cost of the system unpredictable, and potentially puts the attraction at risk.
The golden rule too often forgotten due to our constant exposure to the software of our computers is "do not try to fix something that works." In other words, if the system works fine and does what it is supposed to do, no updating of software and other firmware.
Designing a good Show Control system invariably begins with a thorough analysis of the needs of the attraction. That often goes beyond technical assessment. Understanding artistic, financial and operating aspects is crucial to delivering a great system.
Keep in mind that automation is the core of the system. The failure of one element can stop the attraction. This is why, at Tejix we prefer to use proven industrial solutions in lavish designs. By doing so, we and our customers can move to new exciting projects, rather than be trapped in the "never fully completed" syndrome.