"Dave Plowman (News)" wrote in message
...
In article ,
David Looser wrote:
Indeed, the only things that Betamax and Betacam had in common was the
shell & wrap.

Altering the tape speed and tape material was little different from
what was done to VHS over the years.


It was hugely different! The changes in VHS were all backwards
compatible and the only change in tape speed was to add an LP option.

I never mentioned compatibility. But VHS added a version of separating
luminance and chroma.

Is this a reference to "S-video" aka "Y/C" socketry? Otherwise the method of
seperating Y and C remained the same throughout the development life of VHS.

Went high band. Added FM sound tracks.

In a compatible manner.

They could
well have offered a higher speed option too with some benefits - although
they didn't.

No they didn't.

OTOH there is no compatibility at all between Betamax and Betacam,
beyond the fact that the cassette will physically fit into the machine.

The point I was making was that it was developed out of Betamax. If
Betamax had not existed as a domestic format I'm willing to bet any
subsequent pro cassette based one would have been very different.

Different certainly. But "very" different?, I don't think so.

The drum is a different diameter, the track widths are different,
indeed Betacam has two tracks in parallel, one for luminance and one
for chroma (whilst Betamax uses colour-under).

Thought BetaCam used two colour difference signals. S-VHS used the single
chrominance one.

S-VHS, along with VHS, Betamax, U-Matic, 8mm, Hi8, and indeed virtually
every other sub-broadcast analogue VT system, uses "colour-under" recording
whereby the colour subcarrier and significant sidebands are filtered out of
the composite video, down-shifted to a much lower frequency (in the case of
VHS/S-VHS 627kHz) and directly recorded on the tape along with the
frequency-modulated luminance. The term "colour-under" refers to the fact
that the frequency band occupied by the down-shifted chroma is below that
occupied by the FM'd luminance.

Betacam OTOH time-compresses the baseband R-Y and B-Y signals by 2:1 so that
the two can be time-multiplexed into a single signal. This is then FM'd and
recorded onto a dedicated track. MII uses a similar system.

The linear tape speeds
are quite different, Betacam being a lot faster than any speed
available to Betamax.

Obviously since it is the easy way to increase resolution, etc.

Actually drum diameter makes a lot more difference to resolution, because it
directly controls head-to-tape speed. By comparison linear tape speed hardly
affects head-to-tape speed at all. What linear tape speed does affect is
track width, which translates into SNR. Since Betacam uses two tracks in
parallel a higher linear tape speed is needed to accommodate both.

Linear tape speed also affects the performance of edge-track audio of
course. Although much is made of the superior picture-quality of Betamax
over VHS (mainly due to it's larger drum), it is often forgotten that until
it acquired FM audio it's audio performance was a lot worse than that of VHS
due to it's lower linear tape speed. Sony's attempt to improve it with their
own NR system "BNR" wasn't too successful since BNR is, not to put too fine
a point on it, crap. At least when VHS used NR on the edge-tracks they used
Dolby, but Sony always wanted to invent everything themselves.


David.