Back in the early 1990s when Alesis introduced the first ADAT machines, I wonder if their development engineers envisioned how important those tiny optical ports on the rear panel would become to the pro audio world. The ADAT optical I/O has not only been adopted by countless other companies as a means of multichannel digital audio transport, but has paved the way for more comprehensive forms of fiber optic transmission of digital audio.
There are several distinct advantages to transmitting digital audio via fiber, the most obvious being that multiple channels are carried over a single cable and connector. In the case of ADAT optical, that’s eight channels of 16-bit audio at a sample rate of 44.1 or 48 kHz, or four channels at twice the sample rate. Fiber optic cable is lightweight and (as your telephone provider can attest) has the ability to maintain high audio quality over very long distances. You’ll never have a ground loop problem when using a fiber optic cable because there is no “hard” connection to ground. Fiber is easy to pull through walls or ceilings and requires less effort than copper to bury beneath or fly above an audience. EMI and RFI do not pose issues to fiber optic audio connections, and — though it may not yet be a skill most audio techs possess — it’s way easier to splice a damaged fiber optic line than it is to repair a piece of 40-channel multipair. It’s also easier and cheaper to run a redundant fiber line than it would be to run a redundant copper multipair snake.
Touring at Light Speed
As with just about everything else that has been developed for studio use, fiber optic technology has been modified and adapted for use in live sound reinforcement. These days, mixing consoles intended for live sound routinely include ADAT optical interfaces or provide facility for some sort of expan-sion card with ADAT I/O. However, ADAT I/O is just the tip of the iceberg.
For example, take a look at the LightViper series of digital fiber optic audio products from Fiberplex. Their VIS-1832 is a 32 x 8 analog stage box with onboard Neutrik Combo connectors and preamps for each input, phantom power and 24-bit/96 kHz A/D. Output from the VIS-1832 connects via a single fiber pair (approximately 1/4-inch thick) to a VIM-1832, which serves as a breakout box at the console end of the system. A 300-foot-long reel of cable weighs between 5 and 6 pounds. No backache there. Fiberplex manufactures a mini-YGDAI interface called the VIM-MY32 for use with Yamaha PM5D, M7CL, DM2000 and DM1000 digital mixing consoles that allows the desks to connect directly to a LightViper optical snake without additional cables or electronics. Slick. (Yamaha offers its own MY16AT and MY8AT expansion cards for these desks, featuring 16 and 8 channels of ADAT I/O respectively.)
Also very slick is the Aphex Model 828 Anaconda, a 64-channel, bidirectional digital snake. Designed as an easy and cost-effective way to connect Aphex 1788A remote-controlled mic preamps to any digital recording system, the Anaconda is comprised of two identical interface units on either end of a high-speed fiber run. Each Anaconda interface has eight ADAT optical I/Os, ultraprecise internal word clock and RJ-45 connectors for Ethernet control and metering of Aphex 1788A preamps. Redundancy features include two fiber transceivers and two internal power supplies, all with automatic failure switching.
[Check out the Road Test of RSG’s latest digital snake offering on page 26-Ed.]
Bright Lights, Big Sound Several manufacturers of digital consoles are providing optional fiber connections between their stage boxes and “local” (i.e., front-of-house) racks. In the case of the Soundcraft Vi4 and Vi6, an optional run of fiber allows the stage box to be placed as far as 1.5 kilometers from the local rack. DiGiCo’s D5 Live 56 comes with a remote stage DiGiRack containing 56 A/D and eight D/A converters connected to the console via optical fiber. They also provide 150 meters of fiber cable with the system, so the amount of copper cable in the system is basically reduced to the length of cable between the mic and the stage box. An ADAT I/O card is available as an option. Digidesign’s VENUE digital mixing system accommodates the company’s DSI card, adding eight channels of digital input to the VENUE Stage Rack, either as four AES/EBU pairs on individual XLRs or as a single ADAT optical interface. The DSO card provides eight channels of digital output for the VENUE Stage Rack as four AES/EBU pairs on individual XLRs, as well as an ADAT optical interface — all of which are active at the same time.
Whirlwind’s E Snake is built upon the company’s E Snake Frame (ESF) and E Snake 2 (ES2) master units, which may be connected via fiber optic or Ethernet cable. Each master unit is a hardware frame that can be loaded with 8-channel input and output cards. Since an ESF can hold up to four input and four output cards, the frame is able to simultaneously route 32 inputs and 32 outputs. An ES2 features an integrated power supply and sup-ports any two cards for a total of 16 channels. A variety of analog and digital I/O cards are available, including the MLI (eight analog mic/line inputs), TRMI (eight transformer-isolated mic inputs with Lundahl transformers) and MLO (eight analog outputs). Since the mic/line input cards use Phoenix connectors, Whirlwind offers the ES2J Termination Kit, providing 16 punchouts for mounting of Neutrik D male or female XLR connectors that can be wired to mate with the I/O cards. E Snake may be connected directly to Yamaha PM5D and M7CL consoles, providing control over E Snake mic pres from the Yamaha control surface. The entire E Snake system is expandable via Gigabit Ethernet.
One more thing: In addition to the technical advantages fiber provides over copper, your accountant will love the reduction of weight on the truck.
Steve “Woody” La Cerra is out on tour this summer mixing front-of-house for Blue Öyster Cult. He can be reached via e-mail at Woody@fohonline.com.
