AES47

AES47 describes a standardised method of interconnecting digital audio over a telecommunication standard network.

The development of standards for digitising analogue audio, as used to interconnect both professional and domestic equipment was started in the mid 1980s within the Audio Engineering Society and the European Broadcasting Union. This culminated in the publishing of the AES3 standard (frequently also known as AES/EBU) for professional use as well as, using different physical connections as specified in IEC 60958, within the domestic “Hi-Fi” environment. This work has provided the most commonly used method for digitally interconnecting audio equipment worldwide using physically separate cables for each stereo audio connection.

Introduction

Many professional audio systems are now combined with telecommunication and IT technologies to provide new functionality, flexibility and connectivity over both local and wide area networks. AES47 was developed to provide a standardised method of transporting the existing standard for digital audio (AES3) over current telecommunication interconnection standards that provide a quality of service required by many professional low latency, uncompressed live audio uses. It may be used directly between specialist audio devices or in combination with telecommunication and computer equipment with suitable network interfaces and utilises the same physical structured cable used as standard by those networks.

AES47 details

AES47 (IEC 62365) is an open standard that specifies a method for packing AES3 professional digital audio streams over Asynchronous Transfer Mode networks. The details of these standards can be studied at the Audio Engineering Society standards web site^[1] by downloading copies of AES47-2006, AES-R4-2002 and AES3-2003. AES47 was originally published in 2002 and has been republished with minor revisions in February 2006. Amendment 1 to AES47 has been published in February 2009. This Amendment adds code points in the ATM Adaptation Layer Parameters Information Element to signal that the time to which each audio sample relates can be identified as specified in AES53. The change in thinking from traditional ATM network design is not to necessarily use ATM to pass IP traffic (apart from management traffic) but to use AES47 in parallel with standard Ethernet structures to deal with extremely high performance secure media streams. From work carried out at the British Broadcasting Corporation’s (BBC) R&D department and published as "White Paper 074",^[2] it has been established that this approach provides the necessary performance for professional media production. AES47 has been developed to allow the simultaneous transport and switched distribution of a large number of AES3 linear audio streams at different sample frequencies. AES47 can support any of the standard AES3 sample rates and word size. AES11 Annex D (the November 2005 printing or version of AES11-2003) shows an example method to provide isochronous timing relationships for distributed AES3 structures over asynchronous networks such as AES47 where reference signals may be locked to common timing sources such as GPS. AES53 specifies how timing markers within AES47 can be used to associate an absolute time stamp with individual audio samples as described in AES47 Amendment 1.

An additional standard has been published by the Audio Engineering Society to extend AES3 digital audio carried as AES47 streams to enable this to be transported over standard physical Ethernet hardware. This additional standard is known as AES51-2006.

References