Broadcasting With Audio-over-IP (AoIP)
Transmitting audio over IP networks (LAN, WAN, intranet, Internet) is the most cost-effective way of broadcasting. Whether it is a podcast (multicast, full-duplex), voice conference (unicast, half-duplex) or a livestream event (broadcast, simplex), Audio-over-IP (AoIP) is a part of the solution. Standards like AES67 have refined how communications protocols that transmit audio on IP networks interoperate, so it has become more easy to deploy. Aside from cost savings, it is also available quite readily since all it requires is an Internet connection for most users. This makes the setup and configuration much simpler than before, and it can all be software defined. Cloud network providers also provide robust services that allow the content to be delivered faster based on region, so this provides low latency and speedy delivery of content. This has been able to speed up the workflow as well, which is crucial to broadcasting when it comes to the latest information.
What is AoIP?
Audio-over-IP (AoIP) systems allow you to transmit multiple uncompressed audio signals over IP networks with minimal latency.
There are 3 types of AoIP systems, each operating within different layers of a network. These layers correspond to where a signal is within the network and how devices access that signal.
- Layer 1 — Physical: Provide PPP point-to-point connection through the physical cable.
- Layer 2 — Data Link: Link between two devices in a network.
- Layer 3 — Network: Allows devices to switch between multiple networks using routing protocols.
How AoIP Works
Source audio is analog by nature. This can be livestreaming music or a podcaster giving a talk. The recording of audio is a process that is done in a studio or on location (OB or on site). The acoustics produced from audible sound (20 Hz — 20 kHz) is recorded on a type of media like tape or digital storage device. Mixers, equalizers and amplifiers can be used to condition the sound and remove unwanted distortion and also increase it’s intensity (amplitude). The output is in analog format, meaning it is raw audio of the recording. Now in order to transmit or broadcast this audio requires converting the analog audio to a digital signal. This is where a digital encoder comes into the picture, to perform a ADC or analog to digital conversion. Encoders not only encode digital signals, you can also use them to apply compression on the audio using a specific type of CODEC. The compression can either be lossy like MP3, which sacrifices audio quality for smaller file size and faster transmission rate, or lossless like FLAC, which supports higher fidelity audio files that can be compressed or uncompressed but deliver more quality but requires more bandwidth or storage for files.
For streaming audio, this will also require a process called transcoding. This might require changing the audio and/or video format using a CODEC from one to another e.g. MPEG2 source (broadcast television) to AAC audio (for streaming). The data rate or bit rate of the audio stream can also be adjusted just before transmission. For high quality digital audio, AAC has won out over MP3. AAC is far superior to MP3 in both quality and size. With AAC you get higher quality audio and smaller size as well. Most AoIP uses RTP (Real Time Transport) for audio delivery while using music formats like MP3, Ogg, AAC and WMA (among others). Apple music and YouTube use AAC for their streaming format.
Once the audio has been digitized, it is then ready for transport. Prior to this, there are some systems that encrypt the signal for security purposes (like to protect content from piracy), and require decryption at the client end for playback. Otherwise the content is sent as an IP audio stream ready for delivery to clients. Broadcasters on IP networks want to get the content out to as many locations as possible, so they rely on CDN (Content Delivery Networks). The CDN uses a cloud based architecture which streams the content from regional data centers. This delivers the content from the edge of the network for faster speed and lower latency to clients.
The client software can run as an app on smartphone mobile devices and tablets, and installed programs in laptop and desktop computers. The app or program receives the IP audio stream and then converts the digital signals back to an analog audio format for playback. The best playback are on systems that have high-end speakers with high bandwidth connections. This is just one example of audio delivery on IP networks. There are many different ways to deploy audio using an ecosystem of hardware and software from a single or various vendors. The main advantage is the cost savings due to simpler configuration and more affordable hardware that don’t require dedicated connections. IP networks are also an existing accessible infrastructure that is an open system where available and can reach larger distances.
NOTE: There was no mention of VoIP in this article since some might consider it a part of AoIP. The difference between the two can be a separate article, but basically it has to do with audio quality (AoIP requires more bandwidth for higher quality) and different application (VoIP is for full-duplex one-to-one conversations mostly, AoIP multicast or broadcast audio for a larger reach).
