The benefits of Ethernet-based audio networks

Ethernet is by far the most commonly used networking technology available today, with over 300 million nodes installed worldwide. Over the last few years, a significant trend has emerged in the professional installed sound industry—using Ethernet to distribute high-quality audio. These "audio networks" don't require PCs and aren't streaming audio from compressed files. Rather, they enable components like microphone preamplifiers or powered loudspeakers, to communicate directly and in real-time, over an Ethernet infrastructure. The CobraNet protocol from Cirrus Logic Inc. is one of the available technologies that uses Ethernet to distribute uncompressed audio in this manner.

The audio network trend was not sparked by a desire to be on the cutting edge of technology, but to fill some very real needs. For the past decade, audio technology has been steadily moving from analog to digital technologies, yet the interconnection of the individual components remains in the analog domain. The resultant numerous A/D and D/A conversions can severely limit the performance of the system. Signal quality issues, as well as the cost and complexity required to build audio systems where processing and amplification components are distributed throughout a facility, are no longer of concern with an audio network. The network provides the means for a common, digital interconnection, while at the same time reducing the infrastructure requirements by routing many signals over many fewer cables.

"China has been slow in adopting this type of technology, but recent reports from our sales staff indicate that this is changing swiftly," said Jim Stembel of Crown International, one of the early licensees of CobraNet technology. Just recently, the HangZhou Theater, in the capital of ZheJiang province, installed an audio network, and is using it to route audio and remotely monitor amplifiers. But audio networks are not limited to theaters or performance spaces. They are also used with great success in convention centers, financial offices, churches, government hearing rooms and stadiums. The Hubei Provincial Sports Center Stadium and WuHan Stadium use audio networks for loudspeaker management and AV presentation.

Kris Jackson of International Sales, is the China region export representative for LCS and Symetrix, two CobraNet licensees. According to Jackson, "now that the ground has been broken and there are reference systems in place, we expect to see quite a surge in project bids that include audio networks. We also expect to see more and more networked systems used in smaller installations."

The current construction boom occurring in China presents a unique opportunity for those involved in the construction and systems engineering process to take advantage of the benefits of audio networks. For the builder/engineer or owner of a facility, the greatest benefit of an audio network is the drastic reduction in cabling requirements. A single CAT-5 or pair of fiber optic cables can replace many individual cables, and the very same cable that transports the audio can also carry control and monitoring data. By increasing the number of channels carried over a cable, the infrastructure requirements are greatly reduced. And with many builders now including Ethernet infrastructures as part of the base building design, it is sometimes possible to eliminate the need for a separate audio infrastructure altogether.

With a reduction in the infrastructure requirements, also comes a reduction in the labor effort to install the infrastructure. In traditional audio installations, most of field cable terminations must be soldered. Some 100BASE-T audio networking technologies support as many as 128 audio channels over a single CAT5 cable (1,280 using Gigabit Ethernet), making it possible to replace all of the individual soldered connections with only two crimp-on RJ 45s, one at each end of the cable. The skill required to terminate RJ-45 connectors is minimal compared to the skill required to make a proper soldered connection, leaving a much larger, and more cost-effective labor pool to draw from.

"Networked digital systems are now very cost competitive with traditional analog systems but offer far more flexibility and expansion potential along with much lower installation costs. This will drive systems sales over the coming years," says Jackson.

Flexibility issues
While the infrastructure and cost savings resulting from networked audio systems greatly benefit the owner and project engineers, audio networks also provide great benefit to system designers and users. When using a network to route audio, flexibility is tremendously increased. In a properly designed network, any audio input can be routed to any audio output without having to physically move wires, and without requiring a patchbay. This routing capability enables ease of use for implementing different system configurations on the fly, as well as provides for future changes to be accommodated without having to make hardware or wiring changes.

With an increasing number of campus-wide audio systems covering very large areas, and with the burden of life safety announcements being placed on paging systems, an audio network's ability to support management functionality and fault tolerance, is invaluable. Through network management, a centrally located computer can monitor all network products and alert the system operator if a fault should occur anywhere in the system. The ability of a management system to notify the system operator of the specific component that has failed not only saves precious time, but can also reduce the legwork required to traverse a large area, such as a theme park, in order to diagnose the source of the problem. Designing a system with redundant and/or fault tolerant components provides added confidence in the functioning of the system.

All of the Ethernet-based audio devices are interconnected using standard Ethernet components, like hubs, switches and media converters—components that are available from many different vendors, and at prices that continue to drop. By using technologies developed by the computer industry, audio networking technologies benefit automatically from new Ethernet features and options. Many large companies are competing for top market share, and as these companies advance the state of the art in Ethernet networks, the audio industry can reap the benefits with little or no added development.

The advent of Ethernet switching technology, and the subsequent drop in price per switched port, was of tremendous benefit to audio networking. Ethernet switching hubs have the ability to read the destination address of an Ethernet packet and send the packet out only the port to which the destination device is attached. This is known as unicast addressing, and conserves precious bandwidth on the network.

The figure below shows a simple Ethernet-based audio network in a star-of-stars topology. At the center of each star is an Ethernet switching hub, and at the points of the star are various networked audio devices. Unicast addressing is used to route audio signals from the microphone preamplifier to the signal processor, and then on to power amplifier "B". Whereas multicast addressing consumes bandwidth network-wide, the use of unicast addressing only consumes bandwidth over those links directly connecting the transmitting and receiving devices.

Ethernet audio network in a star-of-stars topology.

While each link between an audio network device and a switching hub still has a bandwidth limit, the overall bandwidth of a switched network scales with the size of the network—more bandwidth is added as the network grows. Bandwidth therefore does not limit the number of audio channels that can be supported network-wide.

Switching hubs can also provide interfaces to other media, such as fiber optic cable, and other networking technologies, like Gigabit Ethernet. And with prices on Gigabit Ethernet ports continuing to drop, it is becoming more and more common to use Gigabit uplink ports to provide an even greater increase in the available bandwidth on the common links between switches.

In addition to the routing flexibility and expansion afforded by switching hubs, some switches also enable the construction of fault-tolerant designs, the segregation of the network into virtual local area networks (VLANs) and traffic prioritization schemes. Because these are all features of switched networks, any or all of these features are also available for use with Ethernet-based audio systems. Practical technologies for distributing audio over Ethernet networks are widely available now, and very soon, these technologies will be available in integrated circuit form. It won't be long before networked audio systems become the rule, rather than the exception.

- Deb Britton
Systems Design Group Director
Peak Audio