On Mon, 6 Feb 2006 22:58:58 -0000, "Martin Underwood" a@b wrote:

Graeme Wall wrote in message
:

In message
"Ronnie Clark" wrote:

It was quite some time before more advanced editing techniques made
it possible to record a whole serial in one go, however I vaguely
recall that it started in the middle of the third series.

Not quite sure what you mean by this, presumably you are referring to
the advent of electronic editing.

What was it that precluded electronic editing by dubbing from one tape to
another, as they did until a few years ago? Was it simply that copying from
one tape to another in the early days brought the quality below acceptible
broadcast standards?


Not exactly.

It was that at the join the to get an imperceptible edit the sync
pulses had to be continuous, and take into account that Broadcast TV
used interlaced scanning with even and odd frames so a complete even
frame should be joined onto a complete odd frame, (& vica -versa) or a
disturbance would be apparent on viewer's sets, (18 million sets would
do a frame roll (at least) &/or display a noise band/ lose line hold.

The VTR's "control track" was also written onto the tape along with
the sound and video, this kept the heads running down the middle of
the tracks written on the tape, and a gap in this might mean the
playback VTR's servos went out of lock and the heads lost their
tracking taking some time, maybe a few seconds, to lock back in.

Also as the splice went through it 's possible that oxide/ adhesive
/clag would be ripped of the tape and cause a head clog. Video tape
was expensive but I doubt if a tape with a physical edit in it would
be re-used to record a new programme because of this risk.

I can't remember seeing physical videotape edits going through on the
telly, though "Non-Sync Cuts" were fairly common into the early '70s,
where millions of home TV's would Colour Kill, and Frame Roll,
especially cutting to/from inserts from Europe or Ireland.

Altogether Nasty.

When PAL colour first came along, that used vertical axis switching in
the colour signal, as well as frame interlacing, so it turned out that
there was a rotating sequence of 8 distinctive frame types, and edits
had to be made such as to preserve that sequence. that can only be
done electronically between two sources which can be synced up
together and IGWS for that matter are also in "colour sync" as well
as.

The signals had to be timed up to be accurate within the odd
microsecond or less, otherwise their would be a bigger and better, and
now *coloured* disturbance. It needed digital electronics to do that.
It can't be done by looking through a microscope, or by varying the
volts on an electric motor.

Perversely the French SECAM system was more rugged in this respect and
editing colour videotapes was simpler for them, they could just go
instantaeneously from play to record if they were B&W synchronous.

However, since their colour information was carried on an FM
subcarrier signals from 2 sources couldn't be simply added together,
(Effect smilar to 2 radio stations on top of one another) so their
vision mixers were more complicated and less satisfactory than ours,
having to decode the signal to RGB and re-encode at all positions in
between 0% and 100% on the fader.

That, at least, is some consolation.

DG