[ProAudio] FeralA - Recordings released encoded with Dolby A

[Bill Whitlock]

Not wanting to digress too far, but your mention of the Nakamichi Dragon again reminded me of my years at Capitol. Capitol was unique in the cassette and LP business because they were so highly vertically integrated. They manufactured their own tape, molded their own cassette shells (or C-zeros as they were called) - and even their own lacquer master discs. Part of QC for the cassette shell molding operation involved using modified (in my electronic development lab, which was not located in the "tower" BTW) Dragons to measure azimuth accuracy and consistency. The auto-azimuth mechanics was fitted with an LVDT linear transducer which then drove a large zero-center analog meter reading +/- 10 arc-minutes full-scale. The shells were generally excellent except when someone shortened the cool cycle on the injection-molding machines, which caused the shells to warp slightly. And, for those unfamiliar with the Dragon, the azimuth-adjusting mechanism was driven by a closed-loop servo that measured phase difference between signals from the two "sub-heads" on each track. It was a wonderful tool for QC.
We also developed a super-low noise LP player to measure noise floor of lacquer master discs to help with lacquer additive formulation. Another player measured the increase (and once-around variations) in tracking force caused by electret charges on the surface of vinyl records created during the pressing operation. The staff rheologist (plastic expert and formulator) used it to test new "anti-static" vinyl additives.
My 7-year stint at Capitol was fascinating because of their heavy investment in R&D - but, by the nineties, they'd pretty much become just another record label.
Bill WhitlockWhitlock ConsultingVentura, CA


-----Original Message-----
From: Mike via ProAudio <proaudio at bach.pgm.com>
To: proaudio <proaudio at bach.pgm.com>
Sent: Tue, Feb 11, 2020 5:23 pm
Subject: Re: [ProAudio] FeralA - Recordings released encoded with Dolby A

Just a side note about Dolby cassettes:


Corey Bailey Audio Engineering<proaudio at baileyzone.net> wrote:

> IIRC, it was Dolby B. Could have been "C" because, at the time, I used
> whatever was built into the record deck & was compatible with my car
> stereo so that I could switch the NR off.

I reviewed a Marantz cassette deck last year, looking for something I 
could recommend to the home-archivists who want to digitize the closet 
full of cassettes of their band's shows from 30 years ago, but who no 
longer have a means to play them and wouldn't spend the bucks on a 
restored Dragon. It has a Noise Reduction switch (for playback only), 
but no B/C switch. I asked their tech support about it, assuming that it 
was Dolby B, and the answer was that it works for either B or C.

I didn't have a good way of testing how good of a job it did on either - 
the best I could do was to compare playback in the Marantz with that of 
my TASCAM 112Mk2, but with several other significant differences between 
playback on the two decks, I couldn't really evaluate the NR decoding.

It turns out that what's in the Marantz (and also in an almost identical 
deck from TASCAM) is that it's not really Dolby, because there are no 
more Dolby decoder chips available, and that's what was used in all the 
cassette decks. This decoder circuit was something that was developed (I 
don't know by who) to approximate the Dolby playback - one size "fits" 
all - though I suppose not Dolby S.

-- 
For a good time call http://mikeriversaudio.wordpress.com
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