TV Home Forum

Audio Description

"Nigel reverses his car" (August 2013)

BA
bilky asko Tyne Tees Look North (North East)
Somewhat unique, the BT Vision box has AD available via a single button push on the remote, appears to the left of the '0', directly opposite the subtitles button. Can't recall seeing the facility being so accessible on any other TV or receiver box.
My Panasonic remote has an AD button.

Both my Hitachi Freeview TV and cack Alba box have an AD button on the remote, despite the latter not working properly; the TV has separate volume controls for the audio and the AD.

Avatar Credit: © Independent Television News. Avatar Subject: Jonathan George Snow HonFRIBA
GE
thegeek Founding member London London
The problem with Audio Description implementation on Freeview is that it isn't done in a way that is backwards compatible with old receivers, as the commentary is broadcast on its own on a separate audio channel.

This means the box needs to be capable of decoding both the normal audio channel and the AD audio channel and mixing them together,

Any idea why it was chosen to do it that way? It seems a bit overly complicated. If the AD is pre-mixed with programme audio you have the ability to lower the volume during things like establishing shots to allow the AD through. If that's still possible it must mean some other kind of data going along with the AD to control programme volume.


I imagine its to save bandwidth. Audio only can be a lower bit rate than something which includes a larger variety of noises/music and it can be in mono rather than stereo.


That's part of it, yep.

When the Audio Described programme leaves the playout suite, it's got regular stereo audio on tracks 1 & 2. Track 3 is the narration, and track 4 is a control track - it sounds a bit like Linear Timecode, but it's actually a data track which contains instructions on what to do with the main programme audio. There's a description of it in this BBC R&D White Paper [pdf] - it's quite robust and can survive being compressed to buggery*.

During the coding & mux process for the DSat platform, there's a bit of kit which does the downmix, and creates a new audio pair. For DTT, it's just transmitted as-is, and the set-top-box does the mix.

Some DTT STBs don't pay any attention to the control track (or lack thereof) and will just mix in whatever it finds on the third audio track. This has caused problems in the past where an OB which was working into another OB (Springwatch Unsprung, IIRC) was using that audio level for director's talkback, and so some viewers who had AD turned on got to listen to it.


* technical term
Avatar credit: SMPTE RP198
DA
David
The way audio description is done on DTT also allows one person to listen to the AD while other people in the same room just listen to the regular audio. This is something that isn't possible with Sky boxes.
MI
Michael
Offtopic, but on my grandfather's Freesat box, to select the English language commentary on S4C rugby games, you had to choose German on the audio options.

Gesundheit.
ST
steveboswell Yorkshire Look North (Yorkshire)
David posted:
The way audio description is done on DTT also allows one person to listen to the AD while other people in the same room just listen to the regular audio. This is something that isn't possible with Sky boxes.


How would you do that?
BA
bilky asko Tyne Tees Look North (North East)
David posted:
The way audio description is done on DTT also allows one person to listen to the AD while other people in the same room just listen to the regular audio. This is something that isn't possible with Sky boxes.


How would you do that?


I believe some TVs (and presumably Freeview boxes) can be set to output AD through the headphone socket, meaning it's just a matter of plugging headphones into the TV to hear the AD separately (or the use of an induction loop plugged into the headphone socket).

Avatar Credit: © Independent Television News. Avatar Subject: Jonathan George Snow HonFRIBA
ST
steveboswell Yorkshire Look North (Yorkshire)
Ah, thanks. I was wondering if they split it through the left/right audio channels, but a dedicated output for the AD sounds like a much better option.

Newer posts