The various methods of transporting audio digitally have expanded over the past decade, leading to a veritable alphabet soup of protocols to chose between. All of them have their advantages and disadvantages to be considered before deploying a system. There are multiple options available as there are multiple problems to be solved. Not all of the things to be considered are simply about the audio transport. There are also factors such as availability of end points, network infrastructure requirements, existing products already installed, and of course cost.
As has recently been discussed during the AVNation Podcast (Episode 151 – Wrap That Pole), the AVNU consortium is starting to announce products that have passed the certification test. AVNU is group of companies that have come together to support and develop the Ethernet AVB protocol. AVB is actually an extension to the basic Ethernet 802.1 protocol, it is not just riding on top of the Ethernet technology it is part of it. A key item they oversee is the voluntary certification for AVB enabled products. This certification is done through the University of New Hampshire Interoperability Lab. A key item is that it is an independent certification lab, not just each member saying that they meet the specification. This certification assures that when one uses AVB products from multiple manufacturers they will be able to stream audio packets between each other via an AVB Bridge (switch).
Notice that did not include control. There are some basic parts of AVB that allow for control of end points, but typically the higher level control that is expected for things such as Digital Signal Processing is still done by each manufacturer or a partnership between manufacturers. This approach is very much the standard for audio transports where each manufacturer custom creates a control solution for their products. However the protocol includes standards for advertising. Both what devices are on the network and what streams they are broadcasting as well as what the receiving capabilities are. However as talker and the listener communicate, the AVB enabled bridge (switch) will start to undertake the process of connecting the two devices together through the switch. The switch will also start to determine the speed at which the data flows through the network and make sure that all of the devices are using the same master clock. This task allows for the system to deliver audio to multiple receivers with proper timing instructions. The data might arrive before it is ready to be played, but the data packet will contain information on when it is to play. Using this technology multiple destinations can receive the same signal at the same time.
One can find more information and details throughout the Internet, but here are a few good suggestions:
- AVNU Knowledge Center
- Extreme Networks AVB Overview
- Crown Audio DriveCore Networked Display with AVB
- Harman Archimedia Networking Overview
Bradford Benn is the Vertical Market Manager for Themed Attractions at Harman. He also regularly teaches about Digital Audio and Networking as part of Synergetic Audio Concepts. The next class will be in November of 2014.