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Discrete Quadraphonic Audio on CED VideoDiscs

 
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kfbkfb



Joined: 15 Nov 2009
Posts: 7

PostPosted: Tue Apr 04, 2017 1:36 am    Post subject: Discrete Quadraphonic Audio on CED VideoDiscs Reply with quote

RCA introduced their Quadradisc (CD-4) system in mid-1972
which provided Discrete Quadraphonic Audio from compatible
(playable in Stereo and Mono) LP and 45 rpm vinyl records.

Around this time, RCA was quoted as saying that they were
planning for Discrete Quadraphonic Audio on their (under
development) videodisc system.

(note - this isn't a "THIS VIDEODISC HAS A MATRIXED
SURROUND SOUNDTRACK" situation)

I've read various technical descriptions of CED (RCA Review,
Audio Magazine etc.) and none of them mentioned anything
other than (Mono compatible) Stereo Audio on CED.

Anyone found any info about how RCA planned to put
(compatible) Discrete Quadraphonic Audio on the
CED SelectaVision VideoDisc?

Kirk Bayne


Last edited by kfbkfb on Sat Apr 08, 2017 12:53 am; edited 2 times in total
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kfbkfb



Joined: 15 Nov 2009
Posts: 7

PostPosted: Tue Apr 04, 2017 2:26 am    Post subject: Reply with quote

Found a reference:

RCA and the VideoDisc:
the business of research
book:

Page 152: (status report in November 1972)

"Goal of four stereo channels: one achieved"


^^^
This fits the time frame of Quadraphonic Audio
being thought of as the "Next Big Thing".

Kirk Bayne
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dmbjunky



Joined: 23 Jan 2017
Posts: 85
Location: Odon, IN

PostPosted: Wed Apr 05, 2017 1:50 am    Post subject: Reply with quote

What's that book like? I've seen it listed but wasn't sure what it was.
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kfbkfb



Joined: 15 Nov 2009
Posts: 7

PostPosted: Wed Apr 05, 2017 10:32 pm    Post subject: Reply with quote

Excellent book, it covers the tortured path the RCA home video
system took from the idea to put Video + Audio on an LP sized disc
to the CED VideoDisc (almost no technical info, mainly stories
about RCA Laboratories dealing with RCA corporate "interference"
while trying to develop practical home video systems).

Its the 2nd item in the CED Bibliography on this website

Kirk Bayne
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kitchensynch



Joined: 24 Feb 2013
Posts: 873

PostPosted: Wed Apr 05, 2017 11:09 pm    Post subject: Reply with quote

Actually, CD-4 discrete 4-channel audio was a JVC invention, and RCA probably picked it up because it didn't require fussy and not so good matrix decoding to accomplish.

The problem is that CD-4 is a physical extension of the stereo phonograph groove and it was subject to wear and tear and the requirement of a special needle on record players. SQ matrixing eventually sort of morphed into 'Dolby Surround' in the end. An early proposal of at least Pioneer was to make the CD standard 4 channel and two sided but Philips and Sony won that battle.

Today all of the quad systems have died and been replaced by various multichannel schemes all based on some form of stereo front 2, center, subwoofer and rears with optional filler speakers. I'm not certain that any of them is really as good as a center and duplication of the front 2 channels at the rear, especially for music.

Sure, it's COOL to hear a noise flying all over your room but it's also nice to have a good stable image with nice dynamics and frequency response. Or at least to these old ears, and I used to wake up to hits of the 70s and 80s on a JVC CD-4 quad that went THUMP and woke you good Smile I use a small Pioneer 15 watt receiver from 1981 with an audio timer and two three way speakers I built from Infinity cabinets and crossovers and they are by my head so I can't ignore them (for at least an hour) Smile

5.1 is nice for live music, if it was encoded well for it. I remember the PBS American Experience episode on Neil Young was a BLAST...
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kfbkfb



Joined: 15 Nov 2009
Posts: 7

PostPosted: Thu Apr 06, 2017 12:40 am    Post subject: Reply with quote

CD-4 required both the record and stylus (line contact type)
to be kept clean to work properly (unfortunately, the public
wasn't trained to keep records and styli clean).

Louis Dorren (inventor of the USA Quadraphonic FM broadcasting
standard and some enhancements to CD-4 playback systems)
posted on www.quadraphonicquad.com often and addressed the
issues of CD-4 wear and tear (the FM carrier amplitude is fine
even after >100 plays ) and cleanliness in several posts.

I haven't looked at the frequency division multiplexing on the
CED VideoDisc system recently to see if the configuration could
accommodate 4 FM carriers in order to offer Discrete Quad, it
would be interesting to know if RCA planned to use a closed loop
noise reduction system back in the early 1970s (before CX
was invented).

Kirk Bayne
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cbertra2



Joined: 29 Dec 2004
Posts: 172

PostPosted: Thu Apr 06, 2017 6:07 am    Post subject: Reply with quote

You can extract rear channel information on any stereo CED disc by using what's called the Hafler hookup. It can be used on any stereo source. I used this back in the 70's on stereo lp records and it works great. It will only work on stereo sources not mono. The more out of phase information between the left and right channels the better. Just get on line and lookup the Hafler Hookup.
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kitchensynch



Joined: 24 Feb 2013
Posts: 873

PostPosted: Thu Apr 06, 2017 8:19 am    Post subject: Reply with quote

This may help you: http://electronics.howstuffworks.com/surround-sound4.htm

From this query: https://www.google.com/search?q=How+Dolby+Surround+works#spf=1
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kitchensynch



Joined: 24 Feb 2013
Posts: 873

PostPosted: Thu Apr 06, 2017 8:32 am    Post subject: OT Hafler, amp/speakers, stuff to know anyway... Reply with quote

PS Hafler is not a quad process, if is a method to divide the stereo 2-channel output into two and as a result basically halves the output power into four speakers, obviously. You have to have separate amplifiers for front and rear, quad, surround etc. You can sum them for a CENTER or SUBTRACT for a subwoofer. However if you run four speakers in a Hafler arrangement you have to watch the impedance of the entire set to prevent clipping and failure of the amplifier. This is why the amp or receiver lists the range in ohms of speakers to use (some will go to 4 ohms, rarely 2...those amps are few and far between or meant for car audio).
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cbertra2



Joined: 29 Dec 2004
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PostPosted: Thu Apr 06, 2017 3:56 pm    Post subject: Reply with quote

You don't have to have separate amps to extract the out of phase audio. Look it up. Its in all stereo recordings. You only need one rear speaker if that's all you have.
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kitchensynch



Joined: 24 Feb 2013
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PostPosted: Thu Apr 06, 2017 5:13 pm    Post subject: Reply with quote

I read about that. It's out of phase. which isn't quite like quad, he called it pseudo quad. I'm not sure but you might call it ambience or other things and similar things seem to have been employed in early A/V receivers in the form of 'surround' sound (JVC did this if I recall).
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kitchensynch



Joined: 24 Feb 2013
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PostPosted: Thu Apr 06, 2017 5:17 pm    Post subject: Reply with quote

Off the path again, I remember that there was a device to remove the vocals from recordings so you could sing over it. Prehistoric karaoke, as it were.
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cbertra2



Joined: 29 Dec 2004
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PostPosted: Thu Apr 06, 2017 6:17 pm    Post subject: Reply with quote

The Hafler hookup will give you the since of being in a large hall.
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SelectaVision420



Joined: 25 Mar 2012
Posts: 1305
Location: Hartford

PostPosted: Fri Apr 07, 2017 8:40 am    Post subject: Reply with quote

now this is an interesting topic!
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kfbkfb



Joined: 15 Nov 2009
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PostPosted: Sat Apr 08, 2017 1:19 am    Post subject: Reply with quote

Stereo source material (including CED) can carry Dolby Surround
encoding (if there's a Dolby Stereo logo in the end credits) which
can be decoded with a Dolby Surround or Dolby Pro-Logic decoder.

I haven't yet tried any (Dolby Surround encoded) Stereo CEDs
(played with my RCA SJT300) through the Dolby Pro-Logic decoder
in my Pioneer AV receiver.

Kirk Bayne
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Jesse Skeen



Joined: 28 May 2004
Posts: 545
Location: Sacramento, CA

PostPosted: Fri Aug 11, 2017 10:10 pm    Post subject: Reply with quote

"Dolly in London" was mixed for SQ, as were a number of other music titles released on Laserdisc on the Pioneer Artists label (Dolly is the only one I know of that was also on CED.) Pro Logic II, or what is now just called "Dolby Surround" on the newer receivers, does a pretty good job decoding SQ.
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kitchensynch



Joined: 24 Feb 2013
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PostPosted: Sat Oct 21, 2017 1:28 pm    Post subject: Reply with quote

Following up on this, if by discrete the OP was thinking CD-4, that was accomplished by stacking the rear signal on top of the stereo information in the record groove, with a separator and the rear signals placed much high in an inauible part of the audio (leaving a groove that carrrried audio above 50 kHz). This required a special needle as well as the demodulator.

The CED 'groove' is not like a phonograph's in which mono is a lateral/side to side movement and the stereo groove is cut in a process that involves a 45-45 matrix cut that modulates the stylus up and down as well as side to side. In fact the CED groove is not reliant on such mechanical methods at all. The stylus merely senses the pattern of the ups and downs and converts them to an electrical signal from which the picture and sound are derived. Laserdiscs use an optical pickup to do something similar.

Discrete sound would not be in the format specifications by the time it was released to the public, much in the same way that 4 channels of audio were an option in the early development of compact discs but never implemented. CD-4 was developed specifically for phonograph records. Matrix systems were developed to allow adding just a decoder, and some where better than others, although Wendy Carlos would beg to differ on most of them as she was involved with them one way of another (and she got her record company to withdraw the SQ pressings of the 4-channel recordings she made because to this). QS/RM, SQ, CD-4 and others made quad recordings a boondoggle from the beginning and the whole thing was dead by 1977...except for this new thing called DOLBY STEREO...

The information for the rear channels in Dolby Surround systems was mostly derived from the right channel information (the carrier/information was there as I recall) and the center is the sum of the left front and right front. A 'subwoofer' signal is split off and the mostly non-directional bass/low frequency audio is used to enhance explosions, rumbling, booty shaking and such. The rear channels are usually quasi-stereo, or mostly mono and could be represented with one or two speakers. The rear is mainly a presense signal that gives the illusion of front to rear depth.

And now...http://www.wendycarlos.com/

Not just about audio, Wendy dabbles in just about everything and as such has OPINIONS. Was even a guy named Walter in the beginning. You will learn something whether you want to or not Smile and will probably be grateful.
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