Settings Dialog Box

The Audio Settings Tab

This tab controls the decoding of the audio streams present.




Downmixing

If you're lucky enough to be in one of the countries that transmit their Audio channels using the Dolby AC3 system (also called MPEG2 audio) - of which the UK isn't yet one - then you can choose the downmixing option to suit your speaker configuration here. DigiTV will then automatically downmix the number of channels that is currently being transmitted to suit your topology.


Digital Output

S/PDIF output forces the sound card to allow undecoded MPEG2 audio to pass though to appear at the S/PDIF connector unmolested. A Dolby Digital 5.1 decoder can then be used to decode the data and feed the speakers independently of the sound card. This option is for use with AC3 audio only since there is no provision made in the S/PDIF specification to cater for other non-linear audio types.


Audio 5.1 Recording

Because the presence of AC3 5.1 audio in some countries (Australia) conflicts with the presence of DVB subtitling in others (Europe) DigiTV includes an option to choose onto which private stream the 5.1 audio should be recorded. The DigiTV media player will automatically compensate for the switching in private streams for 5.1 audio, but not all third party players are so sophisticated. If in doubt, the Audio recording should be set to Private Stream 1. MPEG1 layer I, II and III audio is unaffected by this setting.


Audio Delay

This option has been provided to allow you to alter the delay between the video and audio so that the audio either precedes or succeeds the video by the specified time. This can be useful if you are using amplification equipment that delays the audio so that the video and audio would otherwise be out-of-sync.

The audio delay can be defined on a per channel basis or as a global value. If you select 'Apply per channel' then each time you change channel, the audio delay you previously set for that particular channel will be reapplied. Any adjustments made to this audio delay will automatically be stored as you make them.


Technical

If the currently viewed multiplex (or transport stream recording) has more than one audio channel present, then it can be selected here. Each audio channel has its own PCR (Programme Clock Reference) which will automatically become dislocated from the video PCR if the audio channel is changed.

Technical information about the current audio channel is displayed underneath its PID selector box.


RNIB Audio Description

This is a new service that is being trialled in the UK, and will hopefully make the transition to other European countries and beyond in the near future.

Audio description is a secondary audio channel that is broadcast alongside the main audio channel. It contains the voice of a narrator that describes the visual aspects of a scene during breaks in the normal dialog and so provides a means for visually impaired people to better enjoy the TV programmes.

Of course you don't have to be visually impaired to use Audio Description. Many people with perfect sight will find it useful as it allows them to 'watch' TV while engaged in another activity.

Currently, audio description is only broadcast on a few programmes (mainly soaps) by the major corporations, but UK government legislation means that at least 10% of the broadcast content must contain Audio Description by 2006.