Audio description
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Audio description refers to an additional narration track for blind and visually impaired viewers of visual media, including television and movies, dance, opera, and visual art. For simplicity, this article focuses on the most common venues for description: TV and film. The description narrator talks through the presentation, describing what is happening on the screen during the natural pauses in the audio (and sometimes during dialogue if deemed necessary).
On NTSC-format television in North America, audio description is usually transmitted on the secondary audio program (SAP). However:
- SAP must be turned on to hear the descriptions, which are pre-mixed with the original soundtrack.
- The sound is monaural and not very good, but it works.
- The visual interfaces used to turn on SAP are a problem for blind people.
- There are many technical impediments that pop up from time to time and interfere with passing through a SAP signal on cable and satellite systems.
Pure-digital services (as on satellite and digital cable TV) cannot transmit Second Audio Program. Some satellite and digital-cable platforms offer multiple audio tracks using proprietary systems, and an original SAP channel can be mapped onto one of them. Nonetheless, in practice it is difficult for viewers at home to watch descriptions recorded on SAP via satellite or digital cable unless the satellite or cable operator takes extraordinary measures.
In all broadcast systems in North America, blind and visually-impaired viewers face the accessibility obstacle of having to turn the description track on and off using visual menu systems they can't see.
Audio description (AD) on Digital Terrestrial Television in the United Kingdom is delivered on a separate track making it possible to adjust the AD volume separately from that of the audio from the television programme. Most people receive audio description via digital satellite television however, as you don't need to buy a special box and can just select audio description (or Narrative) via the menus on your satellite set-top box. On satellite television the AD soundtrack is pre-mixed - the traditional way of experiencing description through your TV.
In movie theaters, audio description can be heard using DVS Theatrical and similar systems (including DTS-CSS and Dolby Screentalk). Users listen to the narrator on a wireless headset.
DVDs very rarely include audio description using one of the eight audio tracks available on DVD-Video discs. However, even when an audio description track is available, the visual interface used to turn the description track on or off can be inaccessible to a blind person.
Researchers at the Centre for Learning Technology at Ryerson University in Toronto have been investigating various methods to overcome the limitations of audio description, including audible menus, extended description, first-person narrative and live description.
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