RE: arsclist Dolby and unintended consequences

["Copeland, Peter" <Peter.Copeland@xxxxx>]

Dear Richard,
    My apologies to you and the other listserver subscribers, because I've
struggled with the things so much at "the Beeb" and the National Sound
Archive, I've probably come across more than anyone else. So long as
tape-hiss was the bane of recording to professional standards, so
noise-reduction systems multiplied. If anyone wishes to know, I too have
some of these; but not *all* of them!
    I'm afraid I don't know what is inside the Telefunken High-Com; my notes
on the subject only say that circuits were marketed by Rebis of Great
Britain and D&R Electronics of Holland.
    The Sanyo "Super D" (model N55) attempted to overcome the low-pitched
"pumping" sometimes audible with high-pitched notes (e.g. flutes) recorded
with dBxI, by splitting the frequency-range into two (the crossover being at
2kHz), and compressing each half separately at 2 : 1. Since high frequency
sounds are, in general, lower volume than low-frequency sounds, the
resulting tape sounds toppy and can be confused with dBx. Unfortunately,
practical tape recorders generated intermodulation products behind
high-frequency sounds, which the low-frequency expander brought up on
playback. This gave the curious effect that intermodulation distortion
sounded worse as the recorded volume went DOWN. To reduce saturation
difficulties, high frequencies above 8kHz were compressed even more
strongly, and there was a 1kHz oscillator for aligning this. (Somewhat
analagous to Dolby B, anyway).
    The Toshiba ADRES (Automatic dynamic range expansion system) was
marketed in 1981-2. This is another which I consider combines dBx0 (a
compressor-expander with infinite compression/expansion resolution, models
117 and 119), and Dolby principles. The ADRES compresses at 1.41 to 1
(giving +7dB out for +10dB in); and then adds a Dolby B-type top lift at
lower levels, starting at +1dB about 20dB below lineup level.
    I must also remind you of the JVC ANRS (Audio Noise Reduction System),
which I consider was intended to be compatible with Dolby B, but apparently
did not infringe Dolby's patents. JVC claimed "Dolby B music tapes can be
played back through ANRS", which is obviously perfectly true, literally
speaking! The same system was applied to the RF carriers on JVC CD-4
discrete quadraphonic discs. In 1976 they introduced "Super ANRS", an
additional compander system for the extreme high frequencies on cassette
tapes; but this was overtaken by the Dolby HX-Pro automatic biassing system.
    The BEL system was a cheap version of dBx used in professional studios;
one of our British Library contractors has it on his 24-track. As far as I
know, it's compatible with dBxI.
    Finally, there were several systems published in British amateur
electronics magazines; I won't bore you with these, my finger is getting
tired.
    Well, you asked!
Peter Copeland

-----Original Message-----
From: Richard L. Hess [mailto:ArcLists@xxxxxxxxxxxxxxx]
Sent: 27 June 2002 07:19
To: 'ARSCLIST@xxxxxxxxxxxxxxxx'
Subject: RE: arsclist Dolby and unintended consequences

At 04:03 PM 06/26/2002 +0100, Copeland, Peter wrote:
>And several cassette
>manufacturers effectively combined something like Dolby B and dBx, to get
>around both patents.

What is the Nakamichi High-Com II Noise reduction. There is a unit for sale 
on eBay and for its price I'm not going to buy it to learn about it.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=1361400150

It appears to be yet another compander system. Good grief how many were 
there ? ? ? ?

Cheers!

Richard


**********************************************************************

Now open at the British Library Galleries: 

Trading Places : the East India Company and Asia (to 22 September) 

*********************************************************************
The information contained in this e-mail is confidential and may be 
legally privileged. It is intended for the addressee(s) only. If you 
are not the intended recipient, please delete this e-mail and notify 
the postmaster@xxxxx : The contents of this e-mail must not be 
disclosed or copied without the sender's consent. 

The statements and opinions expressed in this message are those of 
the author and do not necessarily reflect those of the British 
Library. The British Library does not take any responsibility for 
the views of the author. 
*********************************************************************
-
For subscription instructions, see the ARSC home page
http://www.arsc-audio.org/arsclist.html
Copyright of individual posting is owned by the author of the posting and
permission to re-transmit or publish a post must be secured
from the author of the post.