Famed for lifting a lowly dictation medium – the Philips’
compact cassette – to true high fidelity status, does the Dolby B noise
reduction system deserve to be called the noise reduction alphabet for the masses?
By: Ringo Bones
The Dolby B type noise reduction system makes use of single
chain signal processing. The filter is a fixed-gain variable bandwidth device.
The resulting output of the Dolby B-type encoder is a boosted high frequency
output response which gradually flattens out as the high-frequency output level
rises to avoid tape saturation. The Dolby B circuit reduces noise above
approximately 500 Hz and achieves about 8 to 10 dB of noise reduction. Despite
becoming the ubiquitous noise reduction system of choice during the heyday of
the compact cassette, the Dolby B type noise reduction system would not have
existed at all without the help of Henry Kloss.
During his early work in radio astronomy, Ray Dolby got
inspiration on how to make an effective noise reduction system for analog tape
based recording form his own work in trying to extract very weak cosmic signals
from background radiation noise, which later became the working principle
behind Dolby A, a noise reduction system that then became in standard use in
professional recording studios during the start of the Golden Age of Stereo
near the end of the 1950s. Despite its effectiveness, Dolby A was deemed too
complicated for domestic use that domestic hi-fi enthusiasts during the 1950s
up to early 1960s had been doing their do-it-yourself audio recordings on their
consumer-grade open reel tapes without the help of any form of noise reduction
whatsoever.
In 1967, after hearing about Ray Dolby’s famed noise
reduction system – the Dolby A type noise reduction system – which then became
more or less the standard noise reduction system used in every professional
recording studios, Henry Kloss tried to urge Ray Dolby to develop a much
simplified version of Dolby A for domestic use. Dolby later on complied and
developed a simplified consumer version of the Dolby A-type noise reduction
system which we know today as Dolby B, which Kloss originally saw as a boon to
home / domestic open reel tape users. Dolby B then became a runaway success in
the domestic open-reel tape recording front that one of the first open-reel
tape machines intended for home use that adopted the Dolby B type noise
reduction system – the now famed Revox A77 open-reel tape deck – got a very
favorable review on the August 1972 issue of Stereo review magazine that reviewer
Julian Hirsch said “he cannot imagine how the sound quality of this machine
could be improved in any way” when he tested the Revox with the Dolby B noise
reduction engaged. By the way, Dolby B was also used on 8-Track tape systems back then.
Somewhat later, Henry Kloss linked the Dolby B noise
reduction system with a previously unsuccessful Du Pont product – the
chromium-dioxide tape. And thanks to the magical consumer product midwifery
that Kloss excels, these inventions helped make the Philips compact cassette
tape – introduced primarily for office dictation purposes – become a viable
musical storage medium that went on to surpass the vinyl LP in sales during the
very end of the 1970s.
For any type of Dolby noise reduction system
to work properly, the level in playback must be matched to the level in
recording. Without such “tracking”, treble frequencies can sound muffled or
suppressed. Fortunately, the Dolby B type noise reduction system seems to
function more or less adequately if there’s no gross mismatch in playback and
recording levels. And what makes Dolby B very popular to consumers despite the
next generation of Dolby noise reduction systems slated to replace it is that
Dolby B also works adequately in cassette tape playback equipment that are not
equipped with any Dolby noise reduction system whatsoever, thus gaining the
approval of the masses who during the 1980s more than a half of them probably
don’t own a cassette tape playback equipment equipped with any form of Dolby
noise reduction system.
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