Sound Connections in Audio Networking
The world of networked AV is its own kind of Babel. CobraNet, developed by Peak Audio in the mid-1990s and the first successful digital audio networking protocol, had a shot at becoming an industry standard. But while its acceptance by the pro audio industry was fast, it wasn't fast enough to outpace a host of other companies. We look at four of today's prominent protocols.
Pros: Very low, fixed latency; daisy-chain topology; fast reconnection and synchronization along the network; single-channel granularity.
Cons: In general, it requires a dedicated network, though it's compatible with Ethernet equipment that does not also carry control traffic and can be configured to run on a VLAN over a gigabit network. The ring topology for bi-directionality is problematic for large-scale fixed installs because it's limited to 64 channel inputs (though there is no limit in the number of outputs).
Suitable Applications: EtherSound has been seen mainly in live applications, though it can be configured for fixed installations.
Digigram's EtherSound protocol is Ethernet IEEE 802.3x-compliant and supports Layer 2 (physical) network peripherals using standard Cat-5 or Cat-6 cables, fiber optic links, switches, media converters, and other standard Ethernet components. It provides low-latency, bi-directional transmission of synchronized audio channels and control data, with end-to-end transmission time of about six samples (125 microseconds at 48 kHz). It can transport 64 channels of 24-bit/48-kHz PCM audio, plus embedded control and monitoring data, via a single cable. Depending on the sampling frequency, other channel counts are possible, e.g. 32 channels at 96 kHz. Latency is independent of the number of channels transmitted and built-in clock recovery ensures low jitter.
EtherSound offers the option–though in some cases it's a requirement–to wire the network in a daisy-chain configuration. "Some people consider this an advantage that makes for easy wiring racks or speaker clusters," says Gross. "But it is not necessarily a good way to wire a fault-tolerant network."
EtherSound has a much larger footprint in Europe than in North America. The Cité Internationale, in Lyon, France, contains a mix of museums, office space (including the European headquarters of Interpol), restaurants, legislative facilities, and a 3,000-seat auditorium. A sizable IP network was installed on a single-mode fiber backbone with audio signal distribution using EtherSound ES8 and ES220 interfaces.
"Using an audio network was imperative due to the long distances in the building and [RF interference]," says Matthieu Chautain, AV engineer for the project. "We chose EtherSound for several reasons: extremely low latency, number of channels available, flexibility, redundancy, and support of this protocol by a number of manufacturers we work with."
Chautain also pointed out the need for a "clean" network to make sure that points along the way are EtherSound-compatible, citing an unpleasant experience with certain transceivers that resulted in randomly introduced jitter. He advises using an Ethernet analyzer to check for jitter or asking Digigram to vet your transceivers for you. AV
Dan Daley is freelance AV writer and frequent contributor based in Nashville, Tenn.