Audio over IP
Encyclopedia
Streaming audio over IP (AoIP) networks is being increasingly used by broadcasting companies, among others, to provide high-quality audio feeds over distance across an IP network such as the Internet
. The application is also known as audio contribution over IP in reference to the programming contributions made by field reporters and remote events. Audio quality and delay (on duplex transmissions) are key issues for contribution links.
In the past these links have made widespread use of ISDN services but these are becoming increasingly difficult or expensive to obtain in some parts of Europe and are being phased out in others. Many proprietary systems came into existence for transporting high quality audio over IP based on TCP
, UDP
or RTP
. An interoperable standard for audio over IP using RTP now exists.
Within a single building or music venue
, audio over Ethernet
(AoE) is more likely to be used instead, avoiding audio data compression and IP encapsulation
.
development in Glasgow
. A similar system is being installed in the English Regions and will be installed in Wales and Northern Ireland. The audio packets are sent using UDP over the BBC’s Layer3 network. To ensure the audio is not corrupted, Quality of service
(QoS) is set to ensure that the packets are given priority over other network traffic. The platforms used are the WorldNet Oslo for multiple channel contribution and distribution with the WorldCast Horizon deployed in stereo drop-off locations. The aptX algorithm is used with 24 bit depth and 48 kHz sampling. This is a higher specification than normal CDs, and is used to avoid concatenation effects. There have been problems found in the past when NICAM
and MPEG audio paths have been used in sequence in the broadcast chain. The audio heard in the presentation studio has been acceptable, but listeners at home using DAB
have complained about artifacts
. To avoid this, aptX is used at high bit rates. This is a differential PCM system that does not use psychoacoustic processing. It is able to resynchronise after momentary loss of the IP path without noticeable clicking, and is licensed to most Codec manufactures.
Audio over IP is now even used for large sport events: more than 1000 Barix IP Audio Codecs have been recently used to network the various venues of the Commonwealth Games hosted in India.
More advanced audio codecs are capable of sending audio over unmanaged IP networks using automated Jitter
buffering, Forward error correction
and error concealment to minimise delay and maximise packet streaming stability in live broadcast situations over unmanaged IP networks like the internet. Codecs such as the Tieline i-Mix G3 have been used since 2004 at the Olympic Games for live sports broadcasting. These codecs also have the ability to send audio over wireless IP, i.e. 3G
and Wi-Fi, as well as other audio transports like POTS, ISDN, satellite and X.21, and have been used at UEFA and World Cup Soccer tournaments.
Ultra portable audio over IP codecs are also available as a smart-phone applications to send high fidelity broadcast quality audio from remote sites to studios. Applications such as Report-IT Live for iPhone
can send bidirectional 15kHz quality audio live with automated Jitter
buffering, Forward error correction
and error concealment. They can also send 20kHz quality audio recordings from the phone to a studio via FTP.
Due to the exhaustion of IPv4
IP addresses, IP audio codecs should now also be IPv6
compatible to ensure they are capable of connecting over new internet infrastructure. IPv6 infrastructure is being widely deployed to deliver a virtually inexhaustible supply of IP addresses. IPv6 addressing makes it much easier for broadcast codecs to connect to each other directly and perform flexible multi-point connections over IP.
The New Jersey Transit Corporation distributes messages to their customers using Audio over IP Equipment, and IP Audio technology is used in modern train carriages for customer information and messaging now.
Audio over IP is also used in scientific applications, such as the Neumayer Station
in Antarctica, where Barix IP Audio encoders digitize and stream the complete audio spectrum captured by hydrophones under water to the Alfred Wegener Institute for Polar and Marine Research
in Germany.
(EBU) together with many equipment manufacturers has defined a common framework for Audio Contribution over IP in order to achieve interoperability between products. The frameworks define RTP as a common protocol and media payload type formats according to IETF definitions. SIP
is used as signalling for call setup and control. The recommendation is currently published as an EBU Tech 3326-2007 document.
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
. The application is also known as audio contribution over IP in reference to the programming contributions made by field reporters and remote events. Audio quality and delay (on duplex transmissions) are key issues for contribution links.
In the past these links have made widespread use of ISDN services but these are becoming increasingly difficult or expensive to obtain in some parts of Europe and are being phased out in others. Many proprietary systems came into existence for transporting high quality audio over IP based on TCP
Transmission Control Protocol
The Transmission Control Protocol is one of the core protocols of the Internet Protocol Suite. TCP is one of the two original components of the suite, complementing the Internet Protocol , and therefore the entire suite is commonly referred to as TCP/IP...
, UDP
User Datagram Protocol
The User Datagram Protocol is one of the core members of the Internet Protocol Suite, the set of network protocols used for the Internet. With UDP, computer applications can send messages, in this case referred to as datagrams, to other hosts on an Internet Protocol network without requiring...
or RTP
Real-time Transport Protocol
The Real-time Transport Protocol defines a standardized packet format for delivering audio and video over IP networks. RTP is used extensively in communication and entertainment systems that involve streaming media, such as telephony, video teleconference applications, television services and...
. An interoperable standard for audio over IP using RTP now exists.
Within a single building or music venue
Music venue
A music venue is any location used for a concert or musical performance. Music venues range in size and location, from an outdoor bandshell or bandstand or a concert hall to an indoor sports stadium. Typically, different types of venues host different genres of music...
, audio over Ethernet
Audio over Ethernet
In audio engineering and broadcast engineering, Audio over Ethernet is the use of an Ethernet-based network to distribute real-time digital audio....
(AoE) is more likely to be used instead, avoiding audio data compression and IP encapsulation
Encapsulation (networking)
In computer networking, encapsulation is a method of designing modular communication protocols in which logically separate functions in the network are abstracted from their underlying structures by inclusion or information hiding within higher level objects....
.
Examples of use
The BBC has begun using Audio Contribution over IP in Scotland as part of the Pacific QuayPacific Quay
Pacific Quay is an area south of the River Clyde in Glasgow, Scotland. It is located at the former Plantation Quay and Princes' Dock Basin. The Princes' Dock Basin was the largest on the River Clyde when it was opened in 1900. It ceased to be used in the 1970s as the volume of Shipping using the...
development in Glasgow
Glasgow
Glasgow is the largest city in Scotland and third most populous in the United Kingdom. The city is situated on the River Clyde in the country's west central lowlands...
. A similar system is being installed in the English Regions and will be installed in Wales and Northern Ireland. The audio packets are sent using UDP over the BBC’s Layer3 network. To ensure the audio is not corrupted, Quality of service
Quality of service
The quality of service refers to several related aspects of telephony and computer networks that allow the transport of traffic with special requirements...
(QoS) is set to ensure that the packets are given priority over other network traffic. The platforms used are the WorldNet Oslo for multiple channel contribution and distribution with the WorldCast Horizon deployed in stereo drop-off locations. The aptX algorithm is used with 24 bit depth and 48 kHz sampling. This is a higher specification than normal CDs, and is used to avoid concatenation effects. There have been problems found in the past when NICAM
NICAM
Near Instantaneous Companded Audio Multiplex is an early form of lossy compression for digital audio. It was originally developed in the early 1970s for point-to-point links within broadcasting networks...
and MPEG audio paths have been used in sequence in the broadcast chain. The audio heard in the presentation studio has been acceptable, but listeners at home using DAB
Digital audio broadcasting
Digital Audio Broadcasting is a digital radio technology for broadcasting radio stations, used in several countries, particularly in Europe. As of 2006, approximately 1,000 stations worldwide broadcast in the DAB format....
have complained about artifacts
Compression artifact
A compression artifact is a noticeable distortion of media caused by the application of lossy data compression....
. To avoid this, aptX is used at high bit rates. This is a differential PCM system that does not use psychoacoustic processing. It is able to resynchronise after momentary loss of the IP path without noticeable clicking, and is licensed to most Codec manufactures.
Audio over IP is now even used for large sport events: more than 1000 Barix IP Audio Codecs have been recently used to network the various venues of the Commonwealth Games hosted in India.
More advanced audio codecs are capable of sending audio over unmanaged IP networks using automated Jitter
Jitter
Jitter is the undesired deviation from true periodicity of an assumed periodic signal in electronics and telecommunications, often in relation to a reference clock source. Jitter may be observed in characteristics such as the frequency of successive pulses, the signal amplitude, or phase of...
buffering, Forward error correction
Forward error correction
In telecommunication, information theory, and coding theory, forward error correction or channel coding is a technique used for controlling errors in data transmission over unreliable or noisy communication channels....
and error concealment to minimise delay and maximise packet streaming stability in live broadcast situations over unmanaged IP networks like the internet. Codecs such as the Tieline i-Mix G3 have been used since 2004 at the Olympic Games for live sports broadcasting. These codecs also have the ability to send audio over wireless IP, i.e. 3G
3G
3G or 3rd generation mobile telecommunications is a generation of standards for mobile phones and mobile telecommunication services fulfilling the International Mobile Telecommunications-2000 specifications by the International Telecommunication Union...
and Wi-Fi, as well as other audio transports like POTS, ISDN, satellite and X.21, and have been used at UEFA and World Cup Soccer tournaments.
Ultra portable audio over IP codecs are also available as a smart-phone applications to send high fidelity broadcast quality audio from remote sites to studios. Applications such as Report-IT Live for iPhone
IPhone
The iPhone is a line of Internet and multimedia-enabled smartphones marketed by Apple Inc. The first iPhone was unveiled by Steve Jobs, then CEO of Apple, on January 9, 2007, and released on June 29, 2007...
can send bidirectional 15kHz quality audio live with automated Jitter
Jitter
Jitter is the undesired deviation from true periodicity of an assumed periodic signal in electronics and telecommunications, often in relation to a reference clock source. Jitter may be observed in characteristics such as the frequency of successive pulses, the signal amplitude, or phase of...
buffering, Forward error correction
Forward error correction
In telecommunication, information theory, and coding theory, forward error correction or channel coding is a technique used for controlling errors in data transmission over unreliable or noisy communication channels....
and error concealment. They can also send 20kHz quality audio recordings from the phone to a studio via FTP.
Due to the exhaustion of IPv4
IPv4
Internet Protocol version 4 is the fourth revision in the development of the Internet Protocol and the first version of the protocol to be widely deployed. Together with IPv6, it is at the core of standards-based internetworking methods of the Internet...
IP addresses, IP audio codecs should now also be IPv6
IPv6
Internet Protocol version 6 is a version of the Internet Protocol . It is designed to succeed the Internet Protocol version 4...
compatible to ensure they are capable of connecting over new internet infrastructure. IPv6 infrastructure is being widely deployed to deliver a virtually inexhaustible supply of IP addresses. IPv6 addressing makes it much easier for broadcast codecs to connect to each other directly and perform flexible multi-point connections over IP.
The New Jersey Transit Corporation distributes messages to their customers using Audio over IP Equipment, and IP Audio technology is used in modern train carriages for customer information and messaging now.
Audio over IP is also used in scientific applications, such as the Neumayer Station
Neumayer Station
Neumayer-Station was a permanent German Antarctic research base located on Atka Bay. It opened in 1992 replacing the old Georg-von-Neumayer-Station....
in Antarctica, where Barix IP Audio encoders digitize and stream the complete audio spectrum captured by hydrophones under water to the Alfred Wegener Institute for Polar and Marine Research
Alfred Wegener Institute for Polar and Marine Research
The Alfred Wegener Institute of Polar and Marine Research is a scientific organization located in Bremerhaven, Germany. The institute was founded in 1980 and is named after revolutionary meteorologist climatologist, and geologist Alfred Wegener...
in Germany.
EBU N/ACIP
The European Broadcasting UnionEuropean Broadcasting Union
The European Broadcasting Union is a confederation of 74 broadcasting organisations from 56 countries, and 49 associate broadcasters from a further 25...
(EBU) together with many equipment manufacturers has defined a common framework for Audio Contribution over IP in order to achieve interoperability between products. The frameworks define RTP as a common protocol and media payload type formats according to IETF definitions. SIP
Session Initiation Protocol
The Session Initiation Protocol is an IETF-defined signaling protocol widely used for controlling communication sessions such as voice and video calls over Internet Protocol . The protocol can be used for creating, modifying and terminating two-party or multiparty sessions...
is used as signalling for call setup and control. The recommendation is currently published as an EBU Tech 3326-2007 document.