In article , Serge Auckland
wrote:

"Fleetie" wrote in message
...


There were three basic encoding methods for quad records in the 70s. SQ
and QS were matrixed systems which means that the rear channels were
encoded essentially by phase differences in with the front channels.
This would make it reasonably compatible with normal stereo and almost
compatible with mono, important for broadcasting which was mostly on AM
in those days.

The third encoding method, which you allude to in your post was CD4,
which was a carrier system similar to FM in that the front plus rear
channels were mixed in the base-band, and the front-rear encoded on a
carrier and then decoded on playback in a similar way to FM stereo.

IIRC There was more than one 'ultrasonic subcarrier' system. UD-4 also
comes to mind.



The great advantage of CD4 was that separation between front and back
was much greater than a matrix system, and stereo and mono compatibility
was excellent. The great disadvantage of CD4 was that it didn't work!
Under laboratory conditions, with clean, unworn records it would work
fine, but in the real world, with records of varying cleanliness and
wear, it would just collapse. Cartridges had to track up to 45 kHz to
recover the carrier and sidebands, and even one playing by the
blunderbuss cartridges fitted to most record players those days would
render the LP unplayable as a quad LP.

I think the modulation survived moderatey well with one or two carts like
the one Shure did specially for CD4/UD4. But even then I have my doubts
about how many times the end of side could be played before becoming
undecodable. Systems like this seemed doomed from the start to me given the
struggle to play even modest hf levels with LP. Plus, of course, the way
companies at the time couldn't be bothered to take any care when pressing
LPs. Wonder how many LPs would have even had the subcarrier on the walls
when they popped out of the press. ;-

Different labels adopted different encoding standards. DSOTM was on EMI
and they used the SQ system

Not checked, But the 'quad' LP I used as a test disc for the work in the
webpage I put up today is an EMI one using SQ. So confirms the above.


The combination of three incompatible systems that never really worked
properly (there was a fourth, Dr. Duane Cooper's UD4, which however
never came to Europe in significant numbers)and the need for four
loudspeakers arranged in a square around the listener meant that the
quadraphonic craze only lasted a few years in the mid '70s.

Ah, as I recalled above.

IIRC Hi Fi News also did a double LP showing off 'quadrophony' by using a
different method for each LP side. No idea if anyone who bought it was
every able to play all four sides. :-)

Friend of mine at the time got keen on 4-channel (sic) so bought various
LPs, but only the SQ and QS types. But I was unimpressed, so stuck with
stereo.

IIRC There is now a surround-sound version of DSOTM on DVD. No idea how it
compares with the LP, and don't have a multichannel AV system so can't
check.

Slainte,

Jim

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