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Laser Show Systems - Support Equipment

ADAT playback with DMX capability
William R. Benner, Jr., Pangolin Laser Systems

Reproduced from the Spring 1997 - Edition #9 of Laser F/X: Newsletter. © 1997 William R. Benner, Jr, Pangolin Laser Systems. All rights reserved.

ADAT technology offers the single best way to store and reproduce laser shows. With the addition of DMX recording to the ADAT, it is now possible to record all of the elements of a show including beam effects, scan-through effects, lumia and even have house light, smoke machine and other outboard device control.

A brief review of laser recording technologies

Ever since the dawn of laser light shows, laserists have searched for the perfect recording and distribution medium for show material. Even though most laser graphics signals are within the audio frequency range, standard audio recorders could not be used due to the DC nature of laser signals.
Over the years, several techniques have been developed for laser recording including analogue multi-track tape recorders coupled with FM signal encoders, standard video cassette recorders coupled with digital signal encoders, and DAT and CD players coupled with specialised signal encoders. These techniques have not lead to widespread show distribution because of diminished signal quality, poor reliability, proprietary encoding methods and high expense.
Several years ago, Alesis and Fostex introduced the Alesis Digital Audio Tape recorder (ADAT). There were two models: the Alesis ADAT and the Fostex RD-8.
These low-cost, multi-track digital audio recorders were primarily designed for recording studio use. Multiple units could be linked together for up to 128 tracks of audio. And, because of the digital nature of the recording, ultimate signal fidelity is maintained.
Laserists quickly learned that by disassembling the unit and soldering jumper-wires over 24 capacitors, ADATs could be used to record and play back laser graphics signals. When an ADAT is modified in such a way, I call it "laser-ready". It seemed as though prayers had been answered — a low cost, high quality device to record and play back laser show signals. However, since the ADAT was designed for audio signal levels, some external circuitry was usually required to boost the output level as appropriate for scanners and colour devices. Moreover, this method did not address the special needs of laser projector devices such as beam actuators or lumia motor speed controllers.
Recently new models have been introduced: the Alesis ADAT XT and the Fostex CX-8. These are second-generation machines which feature one-piece construction, a much-improved user interface and a tape transport which is four times faster.
Internal circuitry has been completely changed as well. Thanks to surface-mount technology, all ADAT circuitry is now contained on three small boards: the mother board which handles tape transport operation, the CADA board which handles all analogue and digital signals, and the CDAT-ELCO board which handles all differential ELCO signals.
Unlike the previous Alesis ADAT and Fostex RD-8, which only required placing jumpers over capacitors for laser recording, the XT and CX-8 require additional circuitry to be added either internally or externally. This is because most internal components use only a single 5 volt power supply. Even if the capacitors are eliminated, a 2.5 volt offset remains. To make matters worse, the polarity of the input and output signals is inverted compared with previous ADAT models. In other words, images recorded on previous ADATs would play back upside-down and backwards on the XT and CX-8.
Earlier this year, I developed a product called the CADA-MOD. This is a daughterboard which attaches to a board inside the XT or CX-8 and allows these new ADATs to record laser graphics signals. The new ADATs equipped with a CADA-MOD are much more suitable for laser recording than the previous ADAT models because of the on-board adjustments, amplification, filtering, and ability to handle single-ended and differential laser signals. Also, DMX capability has been added to the CADA-MOD to allow full laser show recording including beam cues, lumia speeds, etc.


Answers to myths about ADAT

There have been several myths floating around the industry regarding perceived downside of ADAT playback. These are: having to "cut into" an ADAT, thus voiding the warranty; machine and tape wear-out; and high price. These myths have been primarily propagated by individuals who have never considered all of the facts about ADAT playback.
First, CADA-MOD installation involves minimal disassembly of the ADAT and typically can be completed in less than an hour. The result is a self-contained professional instrument.
As far as warranty, ADAT service centres have been very graceful about honouring warranty of any ADAT, old or new, as long as the modification is done in a professional manner. I do not know of a single instance where warranty service was refused due to modification of an ADAT.
If there are still people who would rather buy an "off the shelf", unit with warranty which is laser-ready, that option has existed since the creation of the CADA-MOD. You can either buy a laser-ready ADAT from Pacific Pro Audio or Laser Spectacles, or have Audio Works or Vision Laser do the CADA-MOD installation for you.
As far as machine and tape wear-out, this mainly has to do with physical environment and the brand and quality of tapes that you use. As with any electronic equipment, a relatively dust-free, temperature-controlled environment is best. According to the Alesis service centres, the best tapes to use are FUJI H471S and Maxell Broadcast (BQ) tapes. Recording head life of 4000 hours is not unheard of when using these tapes. Ampex is the least recommended by service centres. (This is ironic since the ADATs ship with an Ampex tape for your first use.)
The ADATs are quite price competitive as well. While pricing varies depending on your source, a complete laser-ready ADAT XT can be purchased for less than $2,400 US$.


What happens when the next ADAT version comes out?

When the ADAT XT was released, it caught many people off-guard. Many people were unable to immediately take advantage of the new units before the CADA-MOD was released. There is no doubt that the next ADAT version will be just as innovative and will require an internal daughter board which behaves like the CADA-MOD. When this happens, I will design another daughter board.
In a worst-case event, an external encoder/decoder can be constructed which works with the ADAT optical connection. This encoder/decoder can be designed in such a way as to be compatible with all ADAT versions since it would work externally through the optical connection. Since Alesis worked hard to get the optical connection patented, it is unlikely that they will abandon or change this on future ADAT models.


Why not design and use an external encoder/decoder now?

The obvious benefit of an external encoder would be that you can use it with standard ADATs rather than specially modified versions. However, this would be much more expensive since it would duplicate many of the circuits already inside the ADAT. The added expense would eliminate a key ADAT benefit: low cost laser recording.
In addition, statistically speaking there is a decrease in system reliability caused by the increase in parts count and system complexity. If you have trouble with a modified ADAT, there is only one possible cause of the problem: the modified ADAT. But if you have trouble with an external encoder, there are many more potential causes: the ADAT, the encoder, cables between the two, power connections, etc. In a panic situation, it is nice to have the least number of devices to troubleshoot.


Benefits and drawbacks of ADAT and other methods


Many people are successfully using it since 1992. A single tape contains the entire laser show (graphics, sound and possibly beam cues). Shows are authored on the ADAT by recording the output of a producer’s existing equipment so anything can be recorded such as computer output, analogue abstract output, etc. Since the resolution is high, projected image quality is high and since the sample rate is high, advances in scanner and colour technology will still be recordable with the ADAT. The existing channel assignment will continue to be used so compatibility is assured into the future.

Benefits: Relatively low cost (around $2,400 US$). Works with any laser signal source (i.e. it just records voltages). Ease of show creation (multi-track capability is useful). Ultimate in compatibility for past and future shows. Ultimate in projected image quality. Ultimate in convenience, i.e. a singe tape. Ultimate in show sales potential due to large install-base. Alesis and Fostex service centres around the world offer repair in the event of a failure. Multiple-source device from Alesis and Fostex provides competition, stability and options.

Drawbacks: Tape media has a limited number of passes before wear-out. ADAT players will need periodic maintenance. Last-minute changes can be difficult to accommodate.


Lowell CD playback

Relatively new technology. Works with standard audio CD players which have an optical port on the back. Shows are authored by a CD recorder recording the output of a producer’s existing equipment so anything can be recorded such as computer output, analogue abstract output, etc. A single CD contains the entire show (graphics, sound, limited alternate "user bits" for beam control, etc.) Resolution is medium so projected image quality is medium. Sample rate is medium so it is adequate for today’s scanner and colour control needs but probably not adequate for future advancements. Single channel (not left and right stereo) of 12-bit sound, which is adequate audio quality for advertisement, kiosk, etc.

Benefits: Low cost (around $1500* including CD player). Works with any signal source (i.e. it just records voltages). Convenience, i.e. single CD to transport to show. Lifetime, i.e. unlimited number of passes.

Drawbacks: Awkward authoring with CD recorder. Medium sample rate will not be valid for future devices, medium quality monophonic audio is not adequate for all installations such as planetarium shows or movie theatre installations. Last minute show changes are difficult or impossible to accommodate. Very small current install-base so show sales potential to existing sites is minimal. Single-source device with no service network could complicate service issues.


Computer playback (specifically, LD Playback)

Relatively new technology. A Windows-based PC houses standard computer components (hard drive, motherboard, etc.) plus a CD-ROM drive and Pangolin Lasershow Designer Playback board. The LD and ShowTime programs are used to author shows. A single "mixed-mode" CD can be created which contains the entire show (graphics, sound, beam cues, etc.), or external audio and SMPTE source can be used. Resolution is high so projected image quality is high. Sample rate is flexible so compatibility with future advancements is assured.

Benefits: Convenience, i.e. a single CD can contain the entire show or the show can be stored on computer hard disk. Ease of show creation with ShowTime. Simple to accommodate last minute show changes if LD/ShowTime is also installed on the computer. Lifetime, i.e. unlimited number of passes. Some show sales potential due to medium install-base.

Drawbacks: Cost (at least $3,000 US$ for Windows multimedia PC with laser playback-only board and software). Does not work with any signal source – show content can only be created by LD/ShowTime. Single-source device could complicate service options.



For those applications not needing unlimited lifetime media or on-site changes, ADAT is superior in price, signal quality, show creation flexibility, compatibility with past and future devices, sales potential and field service.


Show piracy and protection

I spent many hours pondering how show material can be protected on the various playback alternatives. During that time, I considered encrypting the data on the tape or CD, using specialised encoders for protection, and using optical connections to the projector. After pondering each method, I realised that all of these can be "beat" with a laser-ready ADAT and clip-leads.
The reason is that at some point, we are dealing with analogue signals – analogue signals to control the X-Y position of the beam, and analogue signals to control the colour of the beam. Even if exotic anti-piracy techniques are pursued such as encrypted data transmitted to a laser projector via optical fiber, it would still be possible to connect to the projector’s internal analogue signals and record these signals with a laser-ready ADAT. Since the ADAT only cares about analogue voltages, I could not think of a single scenario that could not be pirated this way.
This is similar to going into a theatre and recording the movie with a camcorder. Since the camcorder records light and sound, there is no way to protect the movie once it is on the screen.
Methods of protecting individual computer-based show components like frames can certainly be devised so that unauthorized users could not use these in a show. But complete shows will have to be protected by ethical, contractual and legal means.


Complete projector and show control

Up until this point, I have mainly been discussing methods of recording laser graphic signals. Graphics are fine for many applications, but as we all know, laser shows also consist of beams, lumia, diffraction and other effects.
Unlike laser graphics which dictate certain signal requirements such as X, Y, etc., these devices can be controlled in a variety of ways. Most laser show companies developed their own way of controlling these.
Several laser show companies have successfully been using the lighting control standard DMX-512 and standard lighting instruments to control these other effects. Based on their success and the input of others, ILDA has recently adopted DMX-512 as the official projector control standard.



In May 1996, I foresaw this need and developed the "CADA-MOD plus DMX" daughterboard. This adds the ability to record and playback DMX-512 on track 6 of the ADAT tapes. This is a revolutionary product, since no similar method of recording DMX-512 had existed up to that point. As we examine the bandwidth requirements for DMX-512, you will see why this was impossible up to that point.


DMX-512: What is it?

DMX-512 is a lighting communications standard. It was created in 1986 as a standardised method for connecting lighting consoles to dimmer packs and was revised in 1990 to allow more flexibility. Since that time, it has become the most common communication standard used by lighting equipment.
There are 512 control "channels". Each of these channels were originally intended to control lamp dimmer levels. You can think of it as 512 sliders on a lighting console, connected to 512 light bulbs. Each slider’s position is conveyed as a number between 0 and 255.
With newer intelligent light fixtures and other devices, DMX-512 is used in a similar fashion where a single "channel" is used for a single function such as lamp brightness, focus, gobo wheel select, gobo wheel speed, etc.
Because laserists may want to use DMX equipment such as lighting consoles and DMX-to-analogue converters, this same "single channel does a single function" philosophy should apply.
Examples of things that fit the "single channel controls a single function" are:

  • Beam actuators that can fade beam positions (or pop into the beam)
  • Shutters and filters that can gradually occlude the beam (or pop into the beam)
  • Lumia motor speed
  • Scan-through device selection
  • Scan-through device speed

Users of DMX-512 do not have to use all 512 channels and, in fact, rarely do. For example, one of my lighting consoles only sends out 12 channels. The fewer channels used, the higher the "refresh" rate. It is possible to get DMX-512 refreshes at up to around 1000 times per second if only 24 channels are used.
To summarise DMX-512:

  • It is a method of connecting a signal controlling source to multiple receivers
  • Serial data is sent up to 4000 feet over three wires
  • Up to 512 variable things can be controlled
  • All channels are continually being "refreshed" so potential safety hazards are avoided


DMX-512 Internals

DMX-512 transmits digital serial data through standard three-wire microphone cables up to 4000 feet. The data is transmitted at 250,000 bits per second using the RS-485 transmission standard over two wires. The third wire serves as a shield to prevent interference with other signals.
There are five pins on a DMX connector: a wire for ground, two wires for "Primary" communication which goes from a DMX source to a DMX receiver, and two wires for a "Secondary" communication which goes from a DMX receiver back to a DMX source. Generally, the "Secondary" channel is not used so data flows only from sources to receivers.
DMX-512 is connected using a daisy-chain connection methodology where the source connects to the input of the first device, the output of the first device connects to the input of the next device, and so on. The standard allows for at least 32 devices on a DMX link. Although each device has an input and output connector, these are merely wired together — no re-transmission or amplification is performed by each device.
Each receiving device typically has a rotary switch which sets the "starting channel number" that is will respond to. For example, if two 6-channel dimmer packs are used, the first dimmer pack might be set to start at channel 1 so it would respond to DMX channels 1 through 6, and the next dimmer pack would be set to start at channel 7 so it would respond to channels 7 through 12.
The actual DMX-512 communications protocol is very simple. It involves transmitting a reset condition (indicating the start of a new packet), a start code and up to 512 bytes of data. Data packets are transmitted continuously. As soon as one packet is finished, another can begin with no delay if desired (usually another follows within 1 ms). If nothing is changing (i.e. no lamp levels change) the same data will be sent out over and over again. This is one of the great things about DMX-512: if for some reason the data is not interpreted the first time around, it will be re-sent shortly.

The DMX-512 specification (also called the USITT DMX512/1990 standard) is available from:
USITT; 10 West 19th Street, Suite 5A; New York, NY 10011-4206; (212) 924-9088, fax 924-9343


How does DMX-512 compare with other possible projector control methods such as MIDI?

When considering possible projector control schemes, these things should be weighed:

  • Cost of implementation and use
  • Availability of devices (consoles, PC add-in boards, devices, software, etc.)
  • Ease of installation and use
  • Relative ease of creating in-house devices, i.e. designing boards yourself
  • Recordability
  • Safety
  • Robustness (fault tolerance and recovery)
  • Usable communication distance

When considering MIDI, the strongest arguments are the availability of devices, and reasonable cost. There are several MIDI lighting consoles and MIDI-to-analogue converters available. PC-add in boards and software are also available. The cost for these units is quite reasonable.
On the downside is distance of communication and system robustness. Since MIDI uses a current loop for communication, distance is limited to 10 meters. As far as robustness, MIDI is a burst protocol which only transmits data when something changes. It is conceivable that a beam actuator could be left "on" if a communication problem caused the "off" command to be missed. Clearly this is unacceptable for laser projectors.
For DMX-512, there are many devices available. These include consoles, dimmers, DMX-to-analogue converters, PC add-in boards and software. Since there is a lot of competition in this field, these are all available at a reasonable cost. The DMX-512 protocol is simple, so proprietary designs are possible using standard microprocessors and components. Usable distance of communication is 4000 feet. Since DMX-512 is a continuous protocol, there is no chance of a "stuck beam" condition as with MIDI. When you consider all of the desirable traits of a laser projector control scheme, DMX seems superior.


How does the ADAT with DMX fit into complete show distribution?

Simply stated, it is the only playback method that addresses past, present and future needs:

  • Creating a show on ADAT can be as easy as recording the output of existing equipment such as a computer, or can be as flexible as multi-pass editing using a high-resolution editing system.
  • Once the show is created, exact duplicates can be easily made using the supplied fiber optic cable and another ADAT.
  • When distribution tapes have been created, they are easily sent to clients through the mail.
  • Since many laserists already have ADAT players, there is a large audience of potential clients.
  • When the tape arrives at the client’s site, they only need to insert it and press play. Since the tape contains all laser, sound and lighting information, no preparation is needed to play a show.

The new ADATs are highly reliable. If there is a problem, the machine troubleshoots itself, presents a message as to what the problem is, and tries to continue functioning anyway. If service is needed, there is an existing network of Alesis and Fostex service centers. This can alleviate the need to fly across the country to a client’s site to troubleshoot a problem.


ADAT, the only sure thing for show distribution

When the ADATs were introduced in 1992, 12K graphics were the standard. Since then Cambridge scanners were introduced and a 30K standard has been adopted. Early this year, when DMX-512 was proposed as the laser projector control standard, the ADAT was configured to record it and this remains the only method of recording and playing back complete shows which include DMX.
Even though several important changes have occurred in the last few years with respect to equipment capabilities, original ADAT tapes recorded in 1992 can still be played back on today’s equipment.
The bandwidth (information capacity) of an ADAT is actually under-utilised by laserists today. As we head into the future, and newer projectors and signal sources become available, ADAT will be able to cope with future requirements. Because of this, ADAT stands as the only sure thing for show distribution.


DISCLAIMER: Some of the information in the Backstage area is provided by the persons or companies named on the relevant page(s). Laser F/X does NOT endorse or recommend any products/services and is NOT responsible for the technical accuracy of the information provided.  We provide this information as a service to laserists using the Backstage area. 

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