Technical information

Audetel was carried by means of encoding the narrative speech into a form which could be transmitted in the Vertical Blanking Interval, like teletext.

A post on TV Forum indicates that lines 21 or 22 (plus their pairs, 334 and possibly 335) were used for this purpose during the trials.

An academic paper giving details of the CELP encoding likely to have been used in the trials is at icsa-speech.org:

The data rate of a single VBI line is approximately 8kb/s - the ICSA paper indicates a limit of 7.6kb/s was in use.