Show Systems - Support Equipment
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
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
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.
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,
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
(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
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.
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.
CADA-MOD plus DMX
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
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
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
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
- 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 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
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
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
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
- 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
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
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
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accuracy of the information provided. We provide this information as a
service to laserists using the Backstage area.
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