I can't answer why, as I waasn't in TVC, and would have gone home when the OU started (if BBC 1 was on a film and then closedown or had already closed for the night).
I would have thought that the TCF crate would have been referenced to station syncs, as would the NC 2 mixer and the OU continuity,
So even a matrix switch shouldn't create too much of a disturbance - maybe the VHS recordings of the time are exaggerating the effect of the reduced delay as the mixer is switched out of circuit.
I saw a lot of these night-time cuts live, and some were similar to that 1990 VHS recording. Though in many cases, the picture jump/audio glitch wasn't that noticeable.
For a standard BBC One/Two closedown, as you know, we'd initially have a period of GLITS & black. Just prior to cutting the vision, they used to show 15 seconds or so of pulse & bar - but at some point in the 90s, pulse & bar was replaced by TCF. When TCF appeared, it was continuous tone rather than GLITS.
Difficult to find a decent example of this on YT, as people generally cut off after the clock/symbol. There's the odd example where they stay until TCF appears, but they tend to edit out most of the GLITS. Here's an example which rejoins at the tail end of GLITS just prior to cutting to TCF (2 mins 20 secs in). Again, slight picture disturbance (this also happened with pulse and bar).
Really odd that after TCF disappears in the above clip, eventually, pulse and bar appears - I don't think I've ever seen this happen. Any ideas what was going on there? It looked as though the video signal was pulled, and then put back, with pulse & bar in place.
Back to TCF - when it was used in the morning, prior to Ceefax, the source seems to be genlocked, as seen here, from 2 mins 25 secs in:
A minor detail which very few will care about. But was always curious about why the night-time version wasn't synched, but the early morning TCF could be transitioned out of quite cleanly.
Last edited by MMcG198 on 13 August 2020 9:53pm