Overcoming audio description’s technical hurdles

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Wednesday, 20 March 2013 14:11pm

Following the 2012 trial on ABC1, Media Access Australia 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 our explanation of how they can be overcome.

Not everyone will receive the AD

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 AD when they didn’t want to

When 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.

We don’t know if 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. As the trial was of receiver-mixed, it is highly unlikely that broadcast-mixed would be chosen at this stage.

There is not enough space left on the spectrum

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 AD in Australia

At this stage, there is no standard which requires all TVs and set-top boxes sold in Australia to be AD-ready. Media Access Australia sits on the Standards Australia committee which is reviewing the standard for digital receivers. Through this, we hope that in future all TVs and set-top boxes sold in Australia will be capable of receiving audio description.

In the meantime, a report by Australian Digital Testing identified almost 250 AD-ready TVs and set-top boxes available in Australia.

The full version of our Delivering audio description in Australia: overcoming technical hurdles briefing paper is available to download:

Media Access Australia offers technical expertise on audio description for the It's as easy as ABC campaign.


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