DETAILED DESCRIPTION The invention relates to tape speed override operation of a helical video tape recorder and, in particular, to a tape speed override system for faithfully recovering helically recorded digital audio signals via helical audio processing channels, while also recovering associated video signals.
In the television industry, and in the course of broadcasting pre-recorded movies, newscasts, commentaries and, particularly, advertisements of varying lengths, it is common for a television broadcast station to have occasions when it is highly desirable to be able to broadcast a recording in slightly less time, or slightly more time, than the length of the recording.
For example, it may be desirable to broadcast a recorded tape having a length of 11 minutes in a time slot of 10 minutes, or in a time slot of 12 minutes.
It is equally desirable to transmit the recording in its entirety, without omitting or repeating, or otherwise editing, any of its contents.
The preferred manner for performing such a process has been to time compress or expand the playback of the recording and thus of the recorded material, generally by a playback process known in the field of television as tape speed override (TSO).
As implied, the tape speed override mode of operation means that the tape is driven at a speed which is a selected percentage greater or less than normal play speed.
In the past, on video tape recorders with longitudinal audio channels such as analog helical recorders, time compression or expansion of recorded material, that is, TSO, were accomplished by varying the linear tape speed according to the desired degree of compression or expansion.
In such recorders, the helically recorded video information is compressed or expanded by skipping or repeating fields or frames of video as required to match the average speed of the playback process.
It follows that the associated audio channels on the longitudinal tracks simply are played back at the correspondingly faster or slower speed of the video tape
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