Over the past decade or so there have been many advances in the world of digital audio networks. If you are planning to update or install a new sound system the choices can be overwhelming. There are several areas where digital transportation of audio can be very cost effective—and also several pitfalls to avoid. We are emerging from a time of multiple standards that, over the next few years, are likely to converge. It's important to know how to plan for digital networking for the future and to understand what will not be going away any time soon.
Many churches' ?rst adoptions of digital audio networking are in stage monitoring. Aviom and Hear Technologies led the way several years ago with companies like Roland and others jumping into the market later. Many of us have used an Aviom or Hearback type of personal monitoring system. At their core, these systems allow multiple channels of audio to be transmitted over simple networking cable and mixed separately by each individual user. These systems are nice for many reasons: you don't need an audio engineer to run every monitor mix from the front-of-house position, there can be as many different mixing stations as required, and there is no audio degradation in having multiple stations. Over time, companies like Roland and Avid have developed variations on the theme and have introduced the ability to adjust each monitor mix station remotely from the front-of-house mixing console while still maintaining local control of the mix.
Monitoring is one great application of digital audio transport, but there are other areas this technology reaches—for example, loudspeaker distribution. As more and more loudspeaker manufacturers transition to self-powered models, it has become popular to use digital audio networks to distribute the signal from the audio system's digital signal processor (DSP) to the loudspeakers. Cobranet and Ethersound are two defacto standards that have been around for some time. Many system designers use Cobranet or Ethersound to send dedicated audio signals to each loudspeaker from the digital signal processor (DSP). This allows the economy that comes from using Category 5-type twisted pair cable to be distributed to each loudspeaker instead of dedicated “analog” audio lines. Furthermore, moving into digital networks can provide redundancy system-wide. Both Cobranet and Ethersound are not limited to loudspeaker distribution. Companies such as Yamaha and Whirlwind have used these technologies to create standalone digital snake systems.
DIGITAL SNAKE ON THE SCENE
Many churches have chosen to add a digital snake system to their existing analog system to replace multi-pair analog cable. Digital snakes are particularly popular in portable systems due to the convenience of pulling a single CAT5 or coaxial cable, instead of a bulky multi-pair analog snake. Digital snakes are a bridge technology that has spanned the gap between older, all-analog systems and newer, all-digital systems. Standalone digital snake systems consist of a stage interface that contains the microphone preampli?ers and the analog-to-digital converters. The converted analog-to-digital signal is then transported through a digital cable to a mixer interface box that converts the digital signal back to analog.
A crucial component of these digital snakes is the preamp control. The microphone preampli?er takes the low-level microphone signal and ampli?es it to line level. In an analog mixing console, the microphone preampli?ers, on each channel, are the start of the analog signal path. They allow the engineer to bring all of the different input levels to a uni?ed level for mixing. In a digital mixing console the microphone preampli?er is the only analog device before the signal is converted to the digital domain. The important question is—where on your digital snake can you control the preampli?er? Some systems have physical knobs on the stage box side of the snake. Others have an interface for computer control via software, or perhaps a dedicated controller that lives at the mix position. The danger is the fact that you still have a second preampli?er control on your mixer. You may encounter a situation where the preampli?er control on the digital snake is set too low and you have to boost the preampli?er on the mixer so high that you get noise.
On the ?ip side, you may have a situation where the digital snake preamp is distorting—and no matter how much you turn down the mixer preampli?er, you will still have distortion. It's best to set all of the mixer's inputs to unity gain for a line level signal, and [then] control the preampli?er in the digital snake.
This is obviously an extra layer of complication for a volunteer sound engineer. For this reason, it is my preference to use a digital snake system that interfaces with the mixing console's preamp control. Most current digital consoles have this feature, including a stage box with the preampli?ers and a digital snake built into the system.
Integrating the digital snake into the digital console is more common now, simply because the technology has had time to mature. A digital console with an integrated digital snake eliminates problems like preamp gain issues mentioned previously.
Manufactures are still split between open standards and proprietary systems.
Ethersound, Cobranet and Dante are popular cross-manufacturer standards, as well as custom proprietary standards from companies like Avid, Digico and Roland.
MADI AND FUTURE EQUIPMENT OPTIONS
One of the most popular open standards for digital audio transport is Multichannel Audio Digital Interface (MADI). MADI is a standard that was originally developed by the Audio Engineering Society (AES) in 1991. At its core, MADI allows up to 64 channels of multi-channel audio to be transmitted over coaxial cable or ?ber. MADI seems to have hit a sweet spot over the past decade—there are very few digital audio consoles or recording systems that do not include a MADI option.
Looking to the future of digital audio networking is exciting. Audio Video Bridging, or AVB, is poised to bridge the ?eld of multiple proprietary networking standards. The advantage of AVB is that its development comes from the Institute of Electrical and Electronics Engineers (IEEE). The IEEE is one of the leading electrical standard bodies in the world, and has developed standards such as LAN (IEEE 802), WIFI (IEEE 802.11) and Bluetooth (IEEE 802.15.1), among others.
Until AVB, all of the audio-related standards, both open and proprietary, have been created solely for the professional audio industry. This isn't a bad thing, however, [since] the IEEE is behind AVB, it bene?ts from the much larger ecosystem that exists in the larger computer networking industry. This means economies of scale in equipment and chipsets should ?lter down to cost savings in the AV industry much faster than previous standards.
Many manufacturers are planning ahead for AVB compliance. The Dante network by Audinate, which has gained popularity in the past couple of years, is already taking steps to be AVB-compliant. For example, Avid has recently released an AVB-compliant stagebox for its SC48 digital mixing system. Meyer Sound has announced that the D-Mitri Digital audio platform is AVB-compliant. BSS has upgraded its Soundweb London product line for AVB functionality, and dBX has added an AVB card to its digital matrix products.
So, how do you proceed? Here are some key things to remember. Analog microphone cables are not likely to go away anytime soon. It is a good idea to keep relying on analog mic lines in the ?oor pockets. However, be sure to include CAT5 or CAT6 cables in the ?oor pockets for future options. Also, don't be afraid to run CAT5 or CAT6 cables to areas such as a foyer or potential over?ow areas.
As far as building infrastructure goes, it's a good idea to start thinking of your audio network in the same manner you think of your computer network. You can have many drops in many locations—just make sure they all come back to a central location within 330 feet. If in doubt, contact a quali?ed AV consultant for addition support. They have the knowledge and experience to steer you in the right direction.
