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CBS Mastersound "DM" (digitally mastered) Half Speed LP's ...

TBone

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#1
https://www.discogs.com/label/367701-CBS-Mastersound

Circa ~1981, early-digital 16 bit mastered LP's.

For either bad sound quality, and/or bad equalization, this series does not have a very good reputation amongst vinylphiles.

I'm not certain that reputation is deserved, perhaps it was recording specific, not certain, I've only about a half-dozen, or so, to evaluate.

They came with this insert ...
1527696586154.png


... which tooted the advantages of digital mastering. I consistently get a kick reading the digital/analog comparison table, which list the S/N ratio as 7.90dB for digital. Obviously, a typo, not certain they fixed that error, every one of my inserts is identical.

3 versions, War Of The Worlds ...
1527697123612.png


Information about the original 1978 recording ...
-Quad 8 Recording Console.
-Studer and MCI 24 track tape machines locked using Maglink synchroniser.
-Original mixes mastered onto a Studer 2 Track 1/4 inch Analogue Tape.

Equipment used at the mastering stage (orig CD) (#91389) ...
-Modified A.T.C. studio monitors with C-Audio power amplifiers and B&W CDM 1 monitors.
-Studer A80 1/4 inch replay machine with Timelord replay electronics.
-Dolby 361 decoders.
-Analogue processors: Focusrite Blue 315 Isomorphic Mastering Equalizer. Focusrite Blue 330 Compressor.
-Analogue interconnects: EMT Barco.
-Prism Dream AD-1 20-bit A-D convertor.
-Optical Interconnect to Sonic Solutions Digital Workstation.
-Additional digital processing TC M5000 Mainframe.
-Mastered direct to CD by Sony CDW 900E CD writer with Super-Bit-Mapping.
-The War Of The Worlds Original Master BASF tape Dolby 1/4 inch.

Dynamically, they measure relatively similar. Tonally they differ ...

1527698387924.png


TB1
 

DonH56

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#2
CBS gained a bad rap/rep for mastering based on a lot of samples for a variety of reasons, including poorly-perceived EQ, poor quality vinyl, etc. I think that was in the 1980's?

If you apply the standard ADC/DAC equation for SNR = 6N+1.76 dB then you get about 7.8 dB for one bit. But the equation does not really work well for a single bit, and of course one-bit delta-sigma converters produce effectively many more bits at the target sampling rate, so the analogy does not hold. Marketing trumps engineering, simply shocking...
 

TBone

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#3
Hi DonH, thanks for responding ...

this is a poorly focussed(sorry) close-up of that chart. 7.90dB vs 64dB.
1527707249648.png
 

DonH56

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#4
Hmmm, hard to read for these old eyes... By "digital master tape" I assume they mean a tape with the bitstream encoded (recorded) upon it. Not sure the point; one way to think of it is that you need need 8 dB of SNR to faithfully recover 98 dB of SNR (for an ideal 16-bit system) at the end after the DAC; normal analog tape won't get you there (more like 60 - 70 dB, maybe 80 dB for a really good system with noise suppression).
 

TBone

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#5
Sorry for the poor quality, shaky hand and all ... I will try to post a more detailed picture when time permits.

They claim 64dB for tape ... the current S/N ratio of my tt rig (static, without LP) measured by my ADC, is also 64dB.
 

restorer-john

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#6
the current S/N ratio of my tt rig (static, without LP) measured by my ADC, is also 64dB.
So you've measured what exactly to come up with that figure? In the absence of a signal, S/N cannot be determined.

You may be considering the residual noise of the system (the TT 'rig'), but if so, what is it referenced to?
 

TBone

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#7
yes, residual noise ... TT rig into ADC, turntable static.

Phono gain is set to achieve about a -4 peak rec.setting plyng ave LP,ADC input set full.

Set so very few LPs require input attenuation, meaning only a few lp with high DR clip without intervention. An orig FMac Rumours clips, very badly, but early LZ originals peak at around -8 ...

... supply a rip if interested.
 
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