Delivering audio description in Australia: overcoming technical hurdles

Campaign partner Media Access Austalia has compiled a briefing paper outlining how Australia’s television industry can overcome the technical challenges of broadcasting audio description (AD).

Below are some of the potential hurdles that have been presented and an explanation of how they can be overcome.

Not everyone will receive the audio description

While only those with an AD-ready digital TV or set-top box will be able receive the audio description, the trial proved that AD could successfully be transmitted to all parts of Australia

Many people received audio description when they didn’t want it

As soon as the AD trial began, the ABC began to receive hundreds of calls from people across Australia complaining that they were hearing AD and didn’t know what it was. This was because the AD function on their TV receiver had been activated at the factory, or had accidentally been turned on since they bought it. In almost all cases, the ABC was able to advise people on how to turn the AD off. We understand that this was not possible on one brand of set-top box, but in a case like this, viewers have the alternative of accessing ABC1 on a mirror channel (21) which did not carry the AD.

This is a problem which is always going to crop up when AD is broadcast, just as people sometimes have the caption function accidentally activated on their TVs. It is not an argument against having a regular AD service.

There is uncertainty over whether AD should be broadcast-mixed or receiver-mixed

This issue has been raised within the TV industry. With receiver-mixed AD, an audio track consisting of the describer’s voice alone is transmitted, and this is mixed with the soundtrack of the program within the viewer’s TV receiver. With broadcast-mixed AD, a second version of the program’s soundtrack is transmitted with the descriptions already mixed in. While Australia could adopt either method, it is difficult to see why broadcast-mixed would be chosen over receiver mixed. The trial consisted of receiver-mixed AD, and many models of TV here support it. Receiver-mixed is also the standard in the UK, which has by far the highest levels of AD on television in the world, and the AD files for many programs could be sourced from there. Receiver-mixed AD (which is broadcast at approximately 64 kbits/sec) also takes up less bandwidth than broadcast-mixed (broadcast at approximately 192 kbits/sec).

Networks do not have enough spectrum capacity to broadcast AD

This was one of the key issues which the AD trial was designed to test. In the Australian broadcasting system, each network is assigned a 7MHz share of the radiofrequency spectrum to broadcast its services, and all of them use this at close to capacity. There has long been an argument put forward by some in the industry that the networks do not have enough spare bandwidth to accommodate audio description.

However, the bandwidth requirements for receiver-mixed AD (which consists of an audio track of the describer’s voice only), are minimal. Prior to the trial commencing, the ABC announced that it would need to switch off some of its digital radio channels while the AD was being broadcast, but in the end this was not necessary. The trial proved that the bandwidth capacity exists for Australian networks to broadcast AD.

There are no receiver standards covering audio description in Australia

This is true, for the moment at least, but is not really an issue given the large number of digital television receivers on sale in Australia which have the capacity to play receiver-mixed audio description. While there were no AD broadcasts in Australia prior to the trial, electronic equipment is often imported into Australia with features designed for overseas markets (such as receiver-mixed AD which is standard in the UK).

A report by Australian Digital Testing, commissioned by the government and released before the trial, identified almost 250 models of AD-ready TV receiver available in Australia, manufactured by Bush, Grundig, Hisense, Samsung, Panasonic, Sanyo, Sony, Sharp and TECO. More will have come onto the market since then. The government’s Digital Switchover Taskforce has also distributed hundreds of ‘talking’ set-top boxes (with AD functionality) to legally blind people as part of its Household Assistance Scheme.

The issue of standards is also being dealt with. The first meeting of a project to revise Australian Standard AS 4933 (covering digital receivers) was held at Standards Australia in January. Media Access Australia is represented on the committee overseeing this project, and including audio description in a revised standard is part of the agenda.