Published in September 2003

Digital Live Performance Audio
By David McNutt

Applications of IT/AV from a live-entertainment and performing-arts perspective.

    Several months ago [May 2003], Sound & Communications published the IT/AV Report, which addressed the current status of IT networks as a transport for audio and video. The scope of the IT/AV Report was the fixed installation and cable infrastructure design of large projects. Because many companies in our industry also have rental companies that serve the corporate and entertainment industry, we thought it might be enlightening to approach this convergence topic from a live-entertainment and performing-arts perspective.

Creeping Up on Us
    The convergence of performance audio and IT has been creeping up on us since before digital signal processing became prevalent. The hope of product developers was that, once a signal was digitized, it would stay digital from transducer to transducer. It didn’t make sense to have to convert it back to analog because the distribution system was analog. This back-and-forth conversion was acceptable when you only had one digital device in the system, but now an entire system can be comprised of many individual digital electronic components. Only recently have digital inputs and outputs become available on products to prevent these multiple, redundant conversions. The idea of using a network to distribute this signal, whether wired or wireless, has also been bounced around for the past eight years. For the purpose of live performance, both fixed-install and portable touring networked systems have advanced, but not quite far enough to say we’ve really succeeded.
    Permanent installations, of course, have always had the luxury of fixed, protected signal paths. As a result, network transports for audio have advanced at a much faster pace in these environments. But even in cutting-edge facilities such as Chicago’s Millennium Park, a new outdoor lakefront concert facility, there’s still the capability to do the “traditional analog” show. Jonathan Laney, senior audio consultant with the Talaske Group, and designer for Millennium Park, believes networks are the path forward in our industry—but not without some obstacles. “The problems right now with digital systems on networks are compatibility and sonic quality issues,” said Laney. “Common protocols and standards among manufacturers are just now beginning to make a seamless system possible without multiple conversions, added latency and compromised sound quality.” Still, the Millennium Park system is an all-digital, front-of-house system that uses CobraNet to distribute audio over an Ethernet network of multi-mode fiber using the best components in the industry. It’s all digital from the stage to the amplifier inputs.

Touring Has Embraced IT, Too
    Touring sound companies have also embraced network signal paths for sound reinforcement. Networked systems tend to be more common in applications where shows reside indoors for longer periods of time and not for shows that go up and down and move from place to place. This has not stopped some, however. For example, Harry Witz, president of db Sound, has been looking for the best portable solution for seven or eight years. “It [networked audio] is certainly of benefit [to us], and companies continue to come up with more and better ideas that work well under road conditions, but they’ve focused mainly on one segment of the system,” Witz stated. The system segment he refers to is the link between the front of house and the stage: That usually provides a thin, optical solution as opposed to a thick bundle of copper. “This is networked audio to most manufacturers. They [manufacturers] usually refer to them as ‘optical snakes’ because they basically are stage-to-console solutions.”
    The benefits of fiber systems for touring sound are quite apparent. One huge benefit is the potential to eliminate ground loops. Every system technician has encountered the situation where the sound system checks out perfectly clean and then someone plugs in a piece of gear on stage, and the system starts humming. With optical snakes, there just aren’t any ground loops. Of course, the new piece of gear may still sound like trash, but that’s a different troubleshooting task. Another benefit of fiber is that it is not subject to electromagnetic or radio-frequency interference. There can be no induced noise in a fiberoptic cable run.

Fiber Issues
    But there are several issues that surround fiber solutions. One big issue of course is the reliability of the connectivity between house and stage. With fiberoptic snakes, it’s all or nothing. In other words, the network either doesn’t work, or it works perfectly. If for some reason it doesn’t work, and you have to replace the fiber cable, the connections are not easy to make and may take half an hour.
    On the other hand, traditional multi-pin snakes can have broken pins, dirty contacts or broken grounds, and if you have to troubleshoot for a single connection out of hundreds, that can take even longer. Although the system technician’s first response is to switch to a spare channel, one still has to find out what’s wrong with the broken channel and get it repaired. With fiber, you simply pick a new strand, polish the end and you have an entirely new snake. The point of all of this is that optical snakes always work properly or they don’t work at all; it’s never a question of just getting by with degraded sound quality and ground loops. The objective is the total reliable quality of the show, not just getting by.
    Another issue with an optical snake is not with the snake itself, but the fact that it only addresses one system segment and therefore can result in redundant, overlapping electronics. For example, an optical snake has mic pre-amps built into the front end. But then, so does the console. The system doesn’t need two sets of mic pre-amps. Why run line levels into the console that you spent so much on for those warm, analog mic pre-amps? And if there are multiple analog and digital components in the system, we wind up back at the multiple conversion issue with which we started.

Durability
    A third question is durability. Products on the road must withstand tremendous wear and tear and only the proven strong ones get to stay. Interestingly, optical cable holds up very well on the road. Kevlar-shielded, military spec, fiberoptic cable has very high tensile strength. “You could tow the tractor with this stuff,” remarked Witz, who recently finished a 100-show comparison tour with three different systems. “Forklifts and vehicles were much more damaging to the copper snakes than the fiber, and the nice thing was the traditional copper snake weighed a thousand pounds, but the fiber you could carry on your shoulder.”
    Of course fiber isn’t the only new medium under consideration. Several companies are experimenting with laser networks to transmit audio. Whirlwind, for example, has developed a system that converts analog inputs to digital signals and outputs them as CobraNet/Ethernet over Cat5 (DCS88). Signals are then routed into a dual-function 10/100 Ethernet Switch/Cat5-to-Optical Converter (ES100-8-FC) for fiber distribution. Converting to optical distribution increases distance limitation of Cat5, but it also allows the signal to be transmitted via laser (DLS1) for those applications where cable runs are difficult. “Now that’s a system that could have application where you have multiple delay stacks and you’re required to trench cable for the event,” said Witz.
The problem is that the price of these new systems is still reasonably high and has not begun to fall, which makes it difficult for low-margin tours to afford. A sound company can trench and discard a lot of cable for the cost of a laser-transmitted audio network.
    All of this said, it’s still traditionally very easy to run cable to the front-of-house; sound companies run their own power to front-of-house anyway. The only question is whether the audio run is a mass of copper or a few strands of fiber.
    But until manufacturers take a broader “system” approach to network audio for touring, the industry standard will probably still tend to remain analog. “To my knowledge, the only company that has yet to provide an all-digital [system] package is DigiCo,” stated Witz. DigiCo, a new live digital console company started by ex-Midas and Klark-Teknik executives, offers a digital console (DC5) with the DSP engine, signal processing and digital I/Os built into the console. With the companion digital stage-to-house package (Stage 56) DigiCo provides a complete mic-to-ampl system from a single manufacturer with only one analog-to-digital-to-analog conversion.
    If networked audio overcomes its relatively few shortcomings for touring systems — and it will — the final analysis will be the same as it always has been for all audio equipment. And that is: what does it sound like? We are an analog species and we like continuously variable, smooth analog sounds. If you think about it, the goal of all digital system users, despite all the digital benefits, is to recreate that natural, analog sound. After all, a violin is still a violin; if it doesn’t sound like one when it gets to the ear, all of the digital-ness is in vain.

David McNutt is president of Chicago-based db Integrated Systems, LLC, and is a member of Sound & Communications’ Technical Council. Send comments to him at dmcnutt@testa.com.