Basic information and the required hardware for AoIP: digital audio transmission via IP network

The digital era is the time for networks, also for audio applications

PA technology has been used as standard in the field of fixed PA installations for a long time now. In the digital age, however, requirements made on PA applications are changing. Buildings should be smarter, cables almost invisible and speakers preferably be controlled from one central control panel. In fact, most digital mixers already feature a network interface. This means that Audio over IP solutions become more and more important, even on stage where analogue systems have dominated the scene so far. They also become increasingly easier to operate and are available at a more and more attractive price. We are going to explain why.

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What does AoIP mean? And what are the benefits?

AoIP stands for Audio over Internet Protocol and is a solution for transmitting digital audio signals via IP network (usually a Local Area Network = LAN). The sound is divided into little digital packets and then transmitted to its destination using the network infrastructure. The IP address ensures that each audio packet is sent to the correct destination (usually a speaker), even when several different destinations are used (multiple speakers). Once there, the receiving station must be able to unzip the audio packets and assign them accordingly.

The audio signal uses the same connection as all other data in the network: e-mails, backups, the merchandise management system, all Internet traffic. Separate lines for announcements and background music are not required.

This solves 2 problems:

The digital AoIP signal replaces analogue signals. The quality of an analogue signal suffers and is susceptible to interference, even with small transmission paths (more than 10 m): the signal is not as strong, the sound reproduction of the high frequencies weakens and it provides a rather dull overall sound. In addition, analogue signals are more susceptible to interference and voltage peaks which cause background noise. Hum loops are also a thing of the past with AoIP transmissions.

The Ethernet cable replaces all other cables. There are various types of transmission and plugs for audio signals: USB, Toslink, XLR, RCA, Speakon. All these solutions primarily mean the following: a lot of special cables and plugs, adapter boxes and again different interfaces such as AES, SPDIF or balanced/unbalanced, mono/stereo. Furthermore, this format jungle also limits the system's flexibility. Each audio channel requires its own cable which is responsible for that signal only and which then leads to the end-user device. Many of these cables and plugs are also quite expensive in comparison. Both problems will be reduced with AoIP solutions. This technology can digitally transmit audio signals in a single network cable and means bye-bye to heavy multicore cables. IP-based transmissions are already part of our everyday life in audio/video communication. IP telephony (SIP), Skype or services like Google Talk all use Voice over IP (VoIP). TV stations broadcast contents via live stream or video on demand. IP network technology also allows you to implement PA projects more easily and flexibly.

Especially in buildings in which a LAN network runs through all the rooms anyway, AoIP is worth considering.

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The advantages of AoIP: expandability and flexibility

Above all, AoIP means freedom for the user:

With an AoIP solution, you are able to distribute audio signals as required. You can address and configure each speaker individually. Depending on the transmission system, it is possible to display all the speakers used in one room on the PC using a routing matrix. For a mutual communication, you only require a connection to the IP network.
The audio components are connected via the network, the signals distributed via virtual link.
Sampling rates can be adjusted as required using AoIP: the user can reproduce music at a higher quality and speech at a decreased quality. Source and audio device must have the same sampling rate.
If audio data are only small data packets, the emphasis is no longer put on the cable quality. The only thing that matters here is the data quality. Depending on the sampling rate setting, the data will be transmitted as produced without any further compression.

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Hardware and prior knowledge required for an AoIP network

In order to implement a PA application via local AoIP, you will need an IP network. A direct LAN connection should be preferred. Other types of network transmission (WLAN, PowerLAN) often result in latencies and thus, are less suitable. For example, an AoIP network can consist of the following components:

An IP network with a wide bandwidth. With increasing data being transmitted via network, the more bandwidth a network connection has to have. The only way to find out the required bandwidth of the network is to write down everything that is being transmitted via the network, including the AoIP PA application.
Routers, switches and access points which ensure a fast and clear distribution of the network signal
Ethernet cables. The operating range is limited to a cable length of approx. 100 m. However, it can be extended via active network components. Alternatively, a fibre optic network can be used to implement greater distances.
Speakers which can operate with IP addresses
Amplifiers which can operate with IP addresses
A sound source, usually a computer
Multi-room systems, in case a multi-room application is required
The power supply of the speakers: this is provided either using a power supply for each speaker or a Power over Ethernet switch

With these components, it is possible to implement a PA application with ceiling speakers. Users should preferably have basic knowledge of computers and network. For example: how an IP address is made up, how a user can access the router from the PC and configure the network. This knowledge may be useful for the installation. For users with little prior knowledge, the Dynamic Host Configuration Protocol (DHCP) is quite useful.

The DHCP assigns IP addresses automatically which facilitates setup and administration of an IP network. Basic knowledge about networks can, however, still be useful for the running operation.

Conclusion: with an increasing number of fixed installations featuring a network, AoIP will also spread and must be further developed.

With the right prerequisites, AoIP is convenient to use and easy to maintain. Particularly for office buildings or educational institutions in which a fast network infrastructure has already been set up, AoIP is usually the most economical solution for your PA application. However, there is also a disadvantage of AoIP: IP networks were initially not designed to be used for real-time transmission of data. We can notice that at every football World Cup: our neighbour watching football via terrestrial TV may cheer 3 seconds before us. A slight delay can be expected if we stream the broadcast because optimum packing and unpacking of files takes a little time, even longer with high quality (i.e. more data). Live events with a latency of a few seconds are unthinkable, too. However, the solution for such projects has already been found. It is called Dante® and is a network protocol specialised for audio transmissions.

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