(1975) CBS Quad LP Insert

[rawmacias]

Just found this in the Old School Quad FB Group (original post by Cykomf Harley):View attachment 84871


Kirk Bayne

I am cataloging some vinyl and came across the exact insert.

 

[rawmacias]

CBS and their sneaky insults to CD-4:
Full dynamic range
Full frequency range
Quiet

IIRC, Sony did similar things when promoting (SQ) quad.


Kirk Bayne

I didn't see any digs about CD-4 on the insert. Plus the insert is Columbia. Had to edit. Just noticed CBS at bottom of insert. That's what I get for speed reading!

 

[kfbkfb]

They're subtle, I've followed the developments related to CD-4 since I first read about it in the 1972-02 issue of High Fidelity (in the Truman HS library) and then a more detailed description in the 1972-09 Popular Electronics:

https://worldradiohistory.com/Archi...idelity/70s/High-Fidelity-1972-02.pdf#page=30
https://worldradiohistory.com/Archive-Poptronics/70s/1972/Pop-1972-09.pdf#page=12
(although, by 1975, CD-4 discs were just as quiet and and had the same dynamic range as mono/stereo/matrix quad discs, the CD-4 frequency range was limited to 15kHz, there's no upper limit for mono/stereo/matrix quad)

I've often wondered if the (relatively low) baseband/sum cutting level in the early years (spring 1972 till the WEA group begin releasing CD-4 in late summer 1973) was to go easy on the 1st generation of CD-4 carts (these early CD-4 discs could have been characterized as "not as quiet" and/or "limited dynamic range")


Kirk Bayne

 

[jaybird100]

They're subtle, I've followed the developments related to CD-4 since I first read about it in the 1972-02 issue of High Fidelity (in the Truman HS library) and then a more detailed description in the 1972-09 Popular Electronics:

https://worldradiohistory.com/Archi...idelity/70s/High-Fidelity-1972-02.pdf#page=30
https://worldradiohistory.com/Archive-Poptronics/70s/1972/Pop-1972-09.pdf#page=12
(although, by 1975, CD-4 discs were just as quiet and and had the same dynamic range as mono/stereo/matrix quad discs, the CD-4 frequency range was limited to 15kHz, there's no upper limit for mono/stereo/matrix quad)

I've often wondered if the (relatively low) baseband/sum cutting level in the early years (spring 1972 till the WEA group begin releasing CD-4 in late summer 1973) was to go easy on the 1st generation of CD-4 carts (these early CD-4 discs could have been characterized as "not as quiet" and/or "limited dynamic range")


Kirk Bayne

It's interesting that, with all the Columbia SQ records I have, none of them have had that insert!

 

[TomC]

I am cataloging some vinyl and came across the exact insert.

Fascinating - now I have to go through my library!!!
TomC

 

[trevorspiro]

As far as I was aware the dynamic range of CD4 discs, particularly the rear channels, was significantly less than ‘normal’ SQ or QS. It has been mentioned above that the rear channel frequency response was curtailed compared to the front, but even a Shibata stylus would have great difficulty reproducing a normal dynamic range of a signal superimposed on the carrier signal, and in addition the demodulator would further compress (reduce the dynamic range) to reduce hiss, a bit like Dolby B.

 

[Doug G.]

In CD-4 discussions, there is a tendency to promote the ideas that the back channels are treated differently from the front channels or that only the back channels are dependent upon the super sonic modulated carriers. These ideas are not true. All four channels are derived from matrixing the audio frequency sum signals with the carrier-derived difference audio signals.

Doug

 

[jaybird100]

In CD-4 discussions, there is a tendency to promote the ideas that the back channels are treated differently from the front channels or that only the back channels are dependent upon the super sonic modulated carriers. These ideas are not true. All four channels are derived from matrixing the audio frequency sum signals with the carrier-derived difference audio signals.

Doug

It's essentially an FM multiplex system, similar to that used for FM stereo.

 

[MidiMagic]

As far as I was aware the dynamic range of CD4 discs, particularly the rear channels, was significantly less than ‘normal’ SQ or QS. It has been mentioned above that the rear channel frequency response was curtailed compared to the front, but even a Shibata stylus would have great difficulty reproducing a normal dynamic range of a signal superimposed on the carrier signal, and in addition the demodulator would further compress (reduce the dynamic range) to reduce hiss, a bit like Dolby B.

The frequency response of all four CD-4 channels are the same. Each CD-4 channel is decoded from both the baseband and the carrier on that side of the groove.

Because the carrier frequency is 30 KHz, and the bandwidths are equal, the baseband occupies the 0 Hz to 15 KHz range and the carrier occupies the 15 KHz to 45 KHz range. The useful frequency range of each decoded channel is probably about 15 Hz to 14 KHz because filters are not perfect and intermodulation is nasty.

The low recording levels and the noise were artifacts of trying to get CD-4 to work with early CD-4 pickups and record wear. Harder vinyls removed most of these problems.