Jim Lesurf:
In article , Dave Plowman (News)
wrote:
The Compact Cassette was introduced as a mono format for dictation
machines, etc. Philips were sensible enough to allow it to be used
under
license but free of charge. But did retain a degree of control over
the
basics.

I'm not sure if this included the use of Dolby B or not. But did
over
the basics like speed.

IIRC They mandated aspects like the physical dimensions (inc. things
like
track widths and spacings), but I'm not sure about which 'electronic'
details they might have defined or limited.

They did try to flog their own 'noise reduction' (DNS?) system which
was
single-ended. But I don't recall that they could (or attempted to)
block or
control the adoption of Dolby. If nothing else, they couldn't have
stopped
anyone from buying a Bolby adaptor box, anyway! Given how good Dolby
was
they probably twigged quite quickly it would be good for sales, and
hence
their own deck/cassette royalties!

Jim

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It wasn't DNS but DNL for Dynamic Noise Limiting - it was single ended
(didn't do anyhting during recording) and didn't work that well
(according to my ears). You could use it with Dolby and get a further
improvement to signal to noise ratio and one or two cassetted decs
allowed this - it didn't catch on so I assume that my impression was not
untypical.

http://audiotools.com/noise.html

https://www.hifiengine.com/manual_li.../ad-1800.shtml

MK