CobraNet Technology: Many of today's audio systems are limited by their complex structure. A true audio network can greatly reduce those problems.
Oct 1, 1997 12:00 PM, Rich Zwiebel
Audio systems have grown significantly more ad-vanced in recent years. Larger systems, which may include a substantial amount of digital sig-nal processing, computer control and monitoring, distributed power amplifiers and steerable loudspeaker arrays, are becoming more common as the industry matures. This growth in capabilities and complexity can be found in all segments of our industry. As we continue to design and deliver more sophisticated systems, our customers have matured and expect more of their systems than at any time before. This is not just occurring in our industry but is being experienced by all technology providers.
Although all of these advances improve the end product, they have also resulted in greater complexity. Most large audio systems now include control systems in addition to the purely audio systems. Distributing power amplifiers have added to the complexity of the audio wiring. Paging, intercom and announcement requirements have increased. Along with the distribution of audio processing and amplification devices, audio sources are frequently located in many locations.
The increased complexity of these systems has created new problems. These systems place greater demands upon the transmission requirements of the system. Adding control and monitoring capabilities to audio processing and amplification products, along with the inclusion of control only products (such as those provided by AMX and Crestron) into systems that were previously exclusively audio systems has added an entirely new layer of wiring to audio systems. More cable and conduit are being included in the design. The additional materials and labor to install and troubleshoot the control system wiring has added to the cost as well as time to install and set up these systems. Distributing sources, processing and amplification has further added to the infrastructure cost. Many of today's consultants and contractors are constrained in their creativity in providing solutions by the additional burden of this infrastructure. It limits them in terms of cost and also in terms of capability.
Peak Audio develops products and technological solutions for the professional audio industry. The limitations of today's infrastructure kept coming up in conversations with industry leaders. Clearly, there was a need for a true audio network. What is an audio network and how does it differ from a cabling system? What features would an ideal audio network include? We discussed audio networking with consultants, contractors, operators and manufacturers. We discovered the following in this study.
A digital network Analog signals are far more susceptible to noise interference than are digital ones. In fact, delivering digital signals over fiber-optic cable creates a completely electrically isolated system that is immune to noise pickup.
Other advantages offered by digital transmission are that digital signals can be carried over inexpensive, unshielded twisted pair cable. It is more cost effective to multiplex digital audio over a single pair of conductors than analog audio. It is also possible to carry other data, such as control data, over the same pair of conductors. The ability to carry multiple channels of audio along with data over a single pair is a big advantage, both in cost and complexity. Digital technology can provide for error detection schemes as well.
As digital audio products become ever more prevalent, transporting audio in the digital domain makes more sense because the need for multiple D-to-A and A-to-D conversions is eliminated. It was clear that any audio network needs to be digitally based.
Multiple-access network The next important issue was to decide whether the audio distribution network was to be a multiple-access network or a collection of point-to-point connections. A multiple-access network allows any node to act as a source, putting audio and control information onto the network. It also allows any node to receive audio and control data. A point-to-point connection allows audio to be delivered from a single point to another single point. (See Figure 1.)
On a multiple-access network, each device is assigned an address. Any audio signal on the network can then be routed to any one or any combination of other devices on the network. This routing can be dynamically assigned. The network, therefore, acts as an audio router, eliminating the need for this typically expensive device. Sources can be located throughout a facility, as can receivers. The result is a highly flexible routing system in which cabling costs are reduced and you eliminate a potential single point of failure in the central router. If this network is bi-directional, all device locations can include both sources and receivers. Devices such mixers can both send and receive over a single cable. (See Figure 2.)
Another advantage is that, because a multiple-access network provides a communications channel to and from each station, all network devices may be monitored and managed from a central point. In a single-access system, the transmitter can control the attached receivers, but because a single-access system is unidirectional, the transmitter cannot monitor the receivers. In fact, it is impossible to determine whether the connection to a given receiver has been broken. For this reason, single-access systems are often augmented with a separate control network used to control and monitor end stations on the distribution system. On a multiple access network, this functionality is built in.
Multiple media Our research further indicated that the network should be compatible with more than one type of medium. One medium should be a low-cost, readily available, common cable type, which is easily terminated with low-cost terminators. Electricians should be familiar with both the cable and terminations. The network should also be able transport data over fiber-optic cable, which is immune to interference induced from outside sources, is able to carry a signal great distances without degradation, and is cost effective.
Although the Audio Engineering Society is developing a standard for control protocol (AES-24), many existing products from professional audio manufacturers currently incorporate control capabilities, using existing communication technologies, and are deployed in the field. Any audio network we came up with had to support these existing protocols as well as the future AES protocol.
Multiple suppliers The industry does not want a proprietary, sole-sourced technology. Proprietary schemes offer the industry less flexibility in selection of products and tend to be more expensive. We decided that using a cost-effective, existing technology was essential. Of course, the audio network must be robust and must not fail. Redundancy schemes must be available and easily implemented.
Other industries have been going down this same path. Most of the facilities that incorporate our systems already are installing network infrastructures. HVAC, lighting, computers and security are just a few fields that are incorporating networks into their system designs. It would be a great benefit to the customer if these same infrastructures could also transport the data for the audio, video and control systems.
Requirement summary The conclusion of our research indicated that an audio network should be able to do the following:
Transport digital audio.
Carry multiple channels of audio and control data over a single pair.
Function as a multiple-access network.
Offer routing capabilities.
Be easily reconfigured.
Be bidirectional.
Be compatible with low-cost, readily available cable and terminators.
Be compatible with fiber-optic cable.
Be available from multiple vendors.
Transport various forms of control data.
Be cost-effective.
Use existing, well-tested technology.
Offer easily implemented redundancy schemes.
Allow for error detection and monitoring of end devices.
Have the ability to make use of existing infrastructure.
Network technology We realized that outside of our industry, networking is a well-established field with many solutions in existence. Rather than start from scratch, only to reinvent the wheel, we embarked on a careful analysis of all of the existing networking technologies.
An obvious advantage of this approach, as compared to developing a proprietary solution just for our industry, is economic. The market for computer networking arguably dwarfs the entire professional audio market. Because of high volumes, off-the-shelf computer networking technology is far more cost effective than a custom solution. An established network technology would offer easy availability of components from multiple sources and a general familiarity, acceptance and knowledge of the technology. These existing technologies would also be well-tested in numerous installations.
The disadvantage is that computer networking technology is optimized for computer applications. There are technical problems in applying computer networking technology to audio applications. These include the need to distribute a sample clock over the network and the need for timely and deterministic network access of audio devices on the network. Some network technologies provide solutions to these requirements more readily than others. Fortunately there are quite a number of computer networking technologies to choose from. It was essential to carefully examine each networking technology to determine if any is appropriate, and if so to select the technology that was the best suited for our needs.
Some of the network technologies we examined included Token Ring, FDDI, ATM, IEEE 1394, 10 Base-T Ethernet, 100 Base-T Ethernet, 100 Base-VG (also known as AnyLAN) and Isochronous Ethernet. (For a detailed analysis of each of these technologies, see Kevin Gross's paper on the subject at www.peakaudio.com.)
Our conclusions pointed to both 10 Base-T and 100 Base-T Ethernet. 100 Base T offers the advantage of 10 times the bandwidth; 10 Base-T is currently more cost effective. Ethernet is the most common network in the world - more than 50 million nodes are installed worldwide. Most other industries have standardized on Ethernet as their transportation medium. Ethernet uses inexpensive CAT 5 cable or, if desired, can be carried over fiber-optic cable. Electricians are familiar with these cable types, and the terminations are simple and low-cost. Ethernet products are available from many vendors, and they have been tested on countless projects. Many existing Ethernet applications are mission-critical, such as life-support systems in hospitals; redundancy schemes exist and are well-tested. Network management systems exist, and it meets all of our requirements. Furthermore, the cost of the components keeps going down! What a great opportunity for the professional audio industry, to be able to piggy-back on the computer industry and enjoy prices that are constantly dropping!
CobraNet The catch with Ethernet is that it was designed for carrying bursty, relatively low-bandwidth computer traffic. If Ethernet is applied to the task of carrying real-time audio, as is done in many PC multimedia applications, the results are less than real-time, primarily because Ethernet uses statistical processes to resolve contention on the network. Because of this, Ethernet can be said to be non-deterministic, especially when carrying heavy loads. This non-deterministic nature means that, although there is a good chance, there is no guarantee that data will be delivered in a timely fashion. Late delivery will result in audio dropouts and discontinuities.
Peak Audio's engineers went to work on this problem, and CobraNet is the result. CobraNet delivers deterministic performance via Ethernet while allowing more than 90% of the network bandwidth to be used.
More than 64 channels of studio-quality audio (20 bit, 48 kHz uncompressed) can be carried on a single CAT-5 cable. More than 500 channels of intercom-grade audio can be carried over this same inexpensive cable. This ability greatly reduces the cost of conduit and cable in a facility (a typical convention center can be reduced by up to $250,000) while increasing the flexibility of the system.
CobraNet allows complete routing flexibility, meaning any input or group of inputs can be routed to any output or group of outputs in any combination in a facility. This allows a system to be reconfigured for different events or for expansion without rewiring. Audio can remain in the digital domain between all digital products on the network, regardless of manufacturer. These products can be located anywhere in the facility that the network goes. CobraNet networks can go over distances of up to 2 km on multi mode fiber, even further on single mode.
Also, the cable can carry control data. CobraNet is not a control protocol, it is a medium for the transport of these protocols. The network currently accepts RS-422, RS-485 and RS-232 control I/O. When AES-24 is established as a standard, it can be carried as well. CobraNet allows control schemes from different vendors to co-exist on the same network infrastructure. The idea here is to reduce the amount of wiring while increasing flexibility. Full redundancy techniques are readily available.
CobraNet-compliant products from various manufacturers can be located throughout a facility. Any node location can provide both sources (inputs to the network) or destinations (audio devices that take audio off of the network). Each CobraNet device is addressable. This means audio from any source can be routed to any destination, or to as many destinations as are desired. Thus routing can be accomplished on the network. Only one low-cost cable is needed to interconnect all audio locations. This same cable carries the audio system control data as well. CobraNet technology has the potential to support delivery of video data as well as audio, though this capability has not been incorporated into any products when this article was written.
New ideas, new products These new capabilities open up many avenues for the system designer. It provides a new level of freedom in locating both centralized and distributed processing. Power amplifiers can be distributed throughout a facility or co-located with loudspeakers without the concern about the additional complexity and cost of cabling and conduit. In fact, the cost of the infrastructure, including cabling, conduit and labor, can be greatly reduced. Because the network can be easily reconfigured, facilities can accommodate different types of events easily. Changes in facilities in the future can be easily accommodated without a need to rewire. As new products are introduced, the systems designer will be able to interface audio processors, amplifiers, self-powered speakers and control products together in a simple, reliable method. Imagine all of the audio products in a sound system interconnecting with a simple RJ-45 connector. There might be 64 channels of audio, control data, monitoring data and clock data all passing through this single connector. This certainly makes wiring the system an easier task.
In order for a network technology to truly benefit an industry, it must be compatible with the products of many manufacturers. A standard technology that is not vendor specific and carries multiple control protocols will advance the industry as a whole and the quality of the systems we provide. This technology is being incorporated into products made by QSC Audio, Level Control Systems, EAW and Crown International, and Rane and Peavey Electronics have announced forthcoming products. Already manufactured units are in successful use at the Sydney Opera House and a large new theme park.
These products and this type of system will allow the audio industry to join other industries in taking advantage of network technology. By using Ethernet, the professional audio industry is taking advantage of developments that are driven by the size of the computer industry. As more flexible, more intelligent systems are designed in the future, the entire industry and customers of our industry will benefit from the advent of networked audio systems.
RAVE (Routing Audio Via Ethernet), QSC Audio's digital audio router system, provides the first practical way for audio data to be routed in real time via standard Fast Ethernet hardware and cabling. Developed in conjunction with Peak Audio, RAVE is the first product on the market to use Peak's CobraNet Technology.
With RAVE, QSC has created a simplified way to overcome the problems that can occur with audio distribution, analog or digital. RAVE units are easy to use, require no complicated configurations and are extremely cost effective. Because RAVE is designed to use standard 100BaseTX Ethernet peripherals, the units can easily be used by consultants and contractors everywhere.
RAVE units recently solved an audio dilemma at Six Flags Over Georgia. The new hour-and-a-half "Gotham City Circus Nights" show had an audio control room located 500 feet (152 m) from the audio sound room. It was a question of how to get audio from "here" to "there" efficiently and reliably.
"Running shielded analog lines would have been costly and not that reliable, and fiber was too expensive," explained T. Neil Garner, audio engineer for the park. "RAVE was the perfect answer. The units provide us with everything we need and then some. We have four channels of audio for the show, three returns to use for audio monitoring, and one channel to use for communication purposes between the two rooms. In addition, they are easy to use and even easier to install."
Individual RAVE units can handle 16 channels of audio inputs or outputs or, as was the case with Six Flags, eight channels of each. In RAVE's simplest form, 16 channels of audio (or eight channels bi-directionally) can be distributed from point A (RAVE unit 1) to point B (Rave unit 2) via Fast Ethernet over a distance of up to 300 feet (91m). Any number of RAVE units can be linked with a maximum total distribution of 64 channels of audio. The only restriction is the distance audio can be distributed over Cat 5 Ethernet cable, approximately 320 feet node-to-node (98 m) or 670 feet (204 m) total. However, the addition of a Fast Ethernet media converter (TX to FX) at the distribution point allows the signal to be distributed via fiber-optic cable, which can provide cable runs of over 2 km (1.24 miles).
That was exactly the case with the half-time entertainment system at Super Bowl XXXI. The RAVE units not only distributed digitized audio conveniently and efficiently on two separate Fast Ethernet networks, but they also facilitated the ability to convert to fiber optics in order to link the far-flung distributed system.
Gary Hardesty, vice president of EAW and entertainment system designer for Super Bowl XXXI, noted, "RAVE components simplified the use of fiber optics and digital audio distribution in a sophisticated system like the one used at the Super Bowl. But I can see them providing benefits to any size distributed system."
Designing RAVE for use with 100BaseTX Ethernet offers numerous advantages. End users understand Ethernet networks. Ethernet networks are economical; the potential savings of 15% to 75% through reductions in cabling, termination, conduit and installation costs is something most end users can understand. Ethernet networks are also flexible - distribution points can be added or subtracted with convenient, off-the-shelf Ethernet peripherals.
Audio routing is also simplified. Each unit distributes blocks of eight audio channels, which can be transmitted or accessed at any point on the network. The routing is determined by two routing switches located on the removable front panel on each RAVE unit. The end result is a system that is flexible, versatile and easily adapted or expanded to service various configurations.
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