Networking technologies introduce new audio quality issues that system designers and sound engineers have to be aware of in order to achieve a high audio quality. However, networking technologies also introduce new and exciting possibilities for system design - along with new quality issues that are not related to audio or sound, but to other fields such as costs, logistics and reliability. This chapter presents a selection of operational quality issues: network implications, Ethernet compliance, redundancy, and cable lengths. Similar to audio quality and sound quality, investors and rental customers can set requirements for the networked audio system to comply to operational quality requirements - with the system designers and sound engineers being responsible for compliance.

In this white paper we propose the following basic definition of a network:

This means that in a networked system, all connections in the network can be set up completely independently from the cabling. To connect a device to a network, it doesn’t matter to which physical connector the device is connected. The functional connections - in the case of networked audio systems all audio connections - are established through routing software.

Network hardware (networked audio devices, Ethernet switches, cables) can be connected physically in three topologies: daisy chain, ring and star. Some network protocols only work in daisy chain or ring topologies, and some work in all topologies - but in all cases, the way the devices in a network are connected within the topology does not affect the software controlled routing. In the networked audio field, examples of networks that require a ring topology are Optocore(*8A), Rocknet(*8B) and Ethersound(*8C). CobraNet(*8D) and Dante(*8E) support all topologies. For more detailed information on audio networks we refer to the white paper ‘an introduction to networked audio systems’ published on the Yamaha website(*8F).

The separation of physical cabling and functional connections in networked audio system has implications for the design and use of networked audio systems.

Design

In the design process of a conventional audio system, functionality and physical cabling are always connected - a change in a system’s function requires a change in the system’s physical cabling and vice versa. When designing functionality, the designer is constrained by the physical cabling possibilities. And if changes to either the functional or physical design are required to be implemented afterwards, the one is always constrained by the other.

In the design process of a networked audio system, the two design jobs can be separated: the functional design can be done first - without physical cabling constraints, and then the physical design - possibly even by another design engineer. The only constraint for the functional design is to stay within the network’s data bandwidth - for networked audio systems usually the maximum number of channels for a single cable in the network, eg. 64 for EtherSound, 512 for Dante. Design changes afterwards can be implemented easily without changes to the cabling system - provided the system’s channel count stays within the available bandwidth. This saves design labour costs and increases the speed of the design process. In many cases it also increases the reliability of the design because the separation of the two jobs make the design process less complex.

Installation & set-up

For the installation or set-up of conventional audio systems, the cable installer needs to have a detailed knowledge of the system’s audio functions - as the way cables are connected affects the system’s functionality. This requires experienced staff and extensive quality management procedures to include not only the physical cabling but also the audio functionality.

With networked audio systems, the cable installer doesn’t need any knowledge on the system’s audio functions - so less experienced staff can be used, and quality management procedures don’t have to include the audio functionality - saving costs and set-up time.

In the field of information technology (IT), Ethernet is the most prevalent world wide standard for networks. All computers, laptops, tablets and smartphones have some form of Ethernet connectivity to enable them to connect to other computers, printers, hard disks and, of course, the internet. For networked audio systems, it makes sense to include Ethernet so all of these functions can be supported additionally to the audio connections. As two other media-related fields - video and lighting control - also have embraced Ethernet as an efficient distribution protocol, a networked audio system that includes Ethernet can also include video and light control over the same cabling - increasing cost efficiency of integrated media systems. Finally, user interfaces increasingly utilize Ethernet, replacing USB and RS232/RS485. Examples are the many tablet apps available to control digital mixing consoles.

There are two ways to provide Ethernet connectivity in a networked audio system: Ethernet embedded systems and Ethernet compliant systems.

Ethernet embedded networked audio systems

A dedicated audio network protocol can include (or embed) an Ethernet tunnel that connects Ethernet ports on selected devices together as one Ethernet network. Examples are Optocore offering a 100Mb tunnel, and Rocknet offering a 10Mb tunnel. The advantage of dedicated audio protocols is that the network is fully managed by the audio designer - offering services to other functions under ‘audio’ supervision. The disadvantage is that the available tunnels mostly offer only unmanaged, low bandwidth Ethernet functionality.

Ethernet compliant networked audio systems

Audio network protocols that use Ethernet as the basic network technology offer the advantage of compatibility with appropiate Ethernet technologies and hardware on the IT market - with the choice of thousands of ‘off-theshelf’ hardware components (switches, media converters, wireless access points). As the IT market is one of the largest markets in the world, it is also the fastest developing market - increasing bandwidth and speed constantly. Fully compliant audio protocols can make use of these developments at very low cost. Examples of low bandwidth Ethernet compliant audio network protocols are EtherSound and CobraNet - both restricted to 100Mb data rates supporting up to 64 channels per cable. An example of a high bandwidth audio network protocol is Dante - using a 1Gb data rate, supporting up to 512 channels per cable. The advantage of Ethernet compliant networked audio systems is that they offer Ethernet connectivity for any Ethernet compliant service as a standard: video, light control, stage automation systems, user interfaces and many more services can be connected without the need for extra hardware. Also, as virtually all personal computers (PC’s) offer an Ethernet connection, modern Ethernet compliant audio networks such as Dante instantly allow all audio channels in the network to be recorded and played back by Digital Audio Workstations (or DAW’s) without the need for any additional interfaces.

Open and closed systems

Some manufacturers of networked audio devices use a proprietary audio network protocol that is only supported by the manufacturer, and not by others. Examples are Optocore - manufactured by Optocore GmbH, and Rocknet - manufactured by Riedel GmbH. The advantage of a closed protocol is that the compatibility between protocol and hardware can be very high - as all devices come from the same manufacturer. A disadvantage of a closed protocol is that a single manufacturer can only offer a limited range of products.

To allow system designers and sound engineers to combine networked audio devices from different manufacturers, an open networked audio protocol can be used - most commonly licensed to many manufacturers of audio devices by a dedicated network technology company such as Cirrus Logic (CobraNet), Digigram (EtherSound) and Audinate (Dante). The advantage of an open networked audio protocol is the high design freedom for the system designer, allowing devices from multiple manufacturers to be used in a system. A disadvantage of an open protocol is the many different implementations, requiring compatibility management.

The choice of an audio network protocol is an important tool for system designers and sound engineers to achieve efficiency in the design processes, and to deliver the desired compliance to customer requirements.

Audio systems using analogue cables to connect the system’s devices are insensitive to cable failures: if one single audio cable breaks, all other audio cables still work. Troubleshooting analogue cabling systems is relatively easy - as all cables can be visually inspected to run from the transmitting device to the receiving device.

With the introduction of multichannel digital audio formats, and later the introduction of networked audio protocols, high amounts of audio channels flow through only one network cable. If such a cable breaks, then all connections are lost - affecting a significant portion of the system. Troubleshooting is not as easy as with analogue cabling because it requires the use of computer software - and a member of staff who knows how to operate the software. This is why networked audio systems - and networks in general - have a redundancy protocol built in that automatically re-routes the connections to a spare cable if any cable in the system fails. All audio network protocols used in a ring or star topology offer proprietary redundancy protocols. For Ethernet compliant protocols, Ethernet itself can offer additional redundancy protocols such as link aggregation and spanning tree(*8G)

It is important for system designers and sound engineers to thoroughly know the redundancy protocols offered by the audio network protocols they are using, and to apply them when they are required. Especially for large scale live events such as corporate events, theatre productions, live concerts and broadcasting, redundancy is a key quality issue for the customer - often of equal importance to audio quality and sound quality.

Redundancy protocols offer a solution for situations where a connection in a networked audio system fails. However, bad connectors on network switches or excessive attenuation due to long cable runs can cause intermittent connection problems that can not be solved by the redundancy protocol. System designers need to carefully study the specifications of the network interfaces, switches, connectors and cables to provide a cabling reliability that matches the customer’s reliability requirements.

Excessive copper (CAT5E, CAT6) cable lengths are a common cause of intermittent connection problems. The determination of allowable lengths is a problem for system designers because many cable manufacturers do not provide maximum length specifications. Depending on the cable and connector quality, the maximum length for CAT5E and CAT6 cables is 100 meters. For mobile use, wear and tear of the cables and connectors, and the use of patch panels, might support shorter cable lengths. For longer distances, the use of fibre cabling can be considered.

For networked audio systems that are installed many times on a temporary basis - such as outside broadcast and live touring systems, road proof network switches and rugged connectors and cables can be used to provide a high reliability. Examples of rugged network connectivity systems for the audio industry are Neutrik EtherCon(*8H), Neutrik opticalCon(*8I), and Connex Fiberfox(*8J).