Wheatstone Audio Transport 

Modern I/O frame based systems have one thing in common – they all replace audio trunk wiring with the ubiquitous CAT-5 or CAT-6 cable. Multiple audio signals are transmitted via CAT-5, and in some case fiber, in topologies that connect various system components like I/O frames and control surfaces.

The exact methodology varies from one manufacturer to another. Systems that use TDM (Time Domain Multiplexed) connections are available in both ring and hub and spoke configurations. One system uses AoIP (Audio over IP) for all of its interconnections. 

Wheatstone has chosen to create what we call a composite system, using a TDM hub and spoke architecture to link system components, combined with AoIP portals for applications that are best served by that approach.

Advantages of the Composite Approach:

TDM architecture is well suited for moving audio between I/O frames. There is very little data overhead, as the data stream does not need the additional header information required for Ethernet based packetized audio. As a result each link has greater capacity (128 audio signals plus control data). There is virtually no latency (<2ms) from any system input to any system output. This also simplifies the system configuration, as each source and destination does not require an IP address. We like to think of our links as “lean and mean” (and fast , robust, and efficient).

The hub and spoke approach means that individual I/O frames can be easily added or removed without upsetting the apple cart. As shown in the system layout above right, individual frames simply plug into network ports, whether they be on our Wheatnet high capacity audio switch or on a network card equipped Bridge Router frame.

Need more than 128 signals between frames? Just add another link. Need redundancy? Add a second Wheatnet with a complete set of failover links.

AoIP is clearly a very efficient way to move audio in and out of a computer (i.e your automation servers and production machines). It is also a good way to distribute an audio feed (like your off air monitor) to various destinations on a LAN, like your PD's or GM's office. And AoIP is certainly a developing technology. New applications such as long distance transport using codecs and public Ethernet will become more widespread.

To capitalize on these existing and soon to arrive applications Wheatstone provides our ET-2001 card (ET-Ethernet Transport). This card installs in our Bridge I/O frame and provides 16 input and 16 output streams in RTP (Real Time Protocol) format. With the Wheatstone wdm driver installed, up to 8 channels of audio can be sent to/from a single PC using its NIC (Network Interface Card). A single network connection replaces the soundcard and associated audio wiring, greatly simplifying installation. Machine commands (Start/Stop commands, etc) are also carried by this same connection.

Typically the ET-2001 card is interfaced through a standard 100baseT Ethernet switch, allowing multiple servers to be connected.  

While we’re on the topic of Ethernet connections, we should mention that we use Ethernet to interface all of our extensive family of hardware control panels.This means that XY controllers, mic remote control panels, and programmable button arrays are all connected to the system using Ethernet. No complicated RS-485 wiring to work out. Our controllers are IP addressable and can be connected through standard hubs and switches.

We also use Ethernet to provide external control from third party systems. Our control protocol is available to any vendor wishing to control our system. The major radio automation vendors and a TV newsroom automation manufacturer have already taken advantage of this capability.