In article , Trevor Wilson
wrote:


"Fleetie" wrote in message
...
Thanks David.

Yeah, you seem to be confirming what I suspected. Even these days, I
think it'd be hard to recover signal above 20kHz from vinyl with good
performance, so I'm still surprised they tried it in the 70s and
expected it to work *in*the*field* with the domestic
blunt-knitting-needle styli (for that's how it's spelt, Jim Lesurf :-)
) of the day.

**Incorrect. CD4 was the only decent quadraphonic system. QS and SQ were
severely limited 'kludges'. Worse, compatability with regular stereo
was a joke. I even kept a couple of SQ recordings, along with the
regular stereo ones as a comparison, to remind me of just how bad
recording studios can get it. A Shibata stylus could easily achieve
what was required for CD4. Even on a properly designed MM cart. MC
carts can do better. MUCH better. By the early 1980s, A decent MC could
manage more than 60kHz.

The above unfortunately omits various significant practical details.

1) That being able to "manage" up to 60kHz doesn't simply mean being able
to detect tiny levels at that frequency. It also means being able to do so
at levels high enough for decent SNR and dynamic range. This sets demanding
limits on tip mass and mechanical impedance at ultrasonic HF. Not just a
matter of stylus profile.

2) That - as per JAES papers of the time - the requirement is also to have
low distortions with these extreme accelerations.

3) The awkward need for this to work right up to the end-of-side. Not just
at the start, or on a test band.

I'd be interested in any measured evidence that modern day MC carts could
play CD4 without wear and recover decent 4-channel. The main thing I notice
about many of them is the absence of data on things like mechanical
impedance or tip mass. One of the potential snags of MC is that a moving
coil might have more mass than a bit of metal modulating a reluctance... I
have wondered if people stopped mentioning this because the results might
be embarassing.

BTW You might find this month's 'Hi Fi News' of interest. Shows some
examples of where a fancy-named stylus profile does not ensure improved
performance. :-) Photos also show a stark difference between an old Shure
stylus and some modern examples.


Correctly done, record wear was somewhat more than a regular stereo
recording. BTW: As service manager for Marantz (Aust) during the 1970s,
I needed to test 4 channel gear daily. Marantz manufactured both SQ and
CD4 stuff. I had a couple of CD4 records and a suitably equipped
turntable (a Technics), cartridge and stylus. Setting up the CD4 units
required that I play a CD4 recording and note the existence of the
carrier frequency and then perform a listening test. Despite the records
being played hundreds of times, the carrier light always lit up, after
alignment. I never much cared for 4 channel audio, but the descrete
nature of CD4 was a vast improvement over the SQ and QS systems.

Well, I assume that other cartridges designed for the task also did it
fairly well. But being able to detect carrier is not the same as being able
to recover the information with the intended snr and distorion levels after
a number of playings. That said, I doubt the LP makers would have wept if
people had found they had to keep buying a fresh copy. ;-

Although one good result of the quadraphonic episode is that it did get
some stylus makers to work at developing ones with low tip mass. e.g. The
Shure M24H was developed in the mid-1970s specifically for replay quad LPs
including CD4, and had a declared tip mass of 0.39mg.


I don't think I'll bother buying the quad LP from Ebay.

**I wouldn't, unless it was a nostalgia thing, or for an investment.
Given the shocking quality of most quadraphonic recordings, most people
would have disposed of them, thus ensuring their rarity and (possibly)
pushing up prices. They're sure not worth listening to.

The few quad LPs I still have (or can find!) essentially sound like normal
stereo, but they are classical, so probably only have a touch of encoded
signal for ambience which passes unnoticed. I did use one of these for the
measurements I've just put onto audiomisc and these showed no obvious signs
that the recording was QS.

Slainte,

Jim

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