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Technical description
DOLBY noise reduction system
The DOLBY noise reduction system substantially
reduces the tape noise (background hiss) which occurs
when a signal is recorded onto magnetic tape.
Tape hiss consists of signals at several frequencies,
mainly in the high and medium ranges, and is particularly
disturbing when quiet passages are reproduced.
When the DOLBY noise reduction system is in use, the
recording level of low-volume medium and high
frequencies is raised during the recording process.
During playback these signals are reduced by an equal
amount. As a result the reproduced signal is identical to
the original source signal, but the level of background
hiss produced by the tape itself is reduced substantially.
The most popular noise reduction system is
DOLBY B NR (NR = Noise Reduction).
The DOLBY C NR noise reduction system is a newer,
significantly improved variant of DOLBY B NR.
DOLBY C NR works on a similar principle to that of
DOLBY B NR, differing only in the characteristic curves
of the encoding and decoding processes.
Whereas DOLBY B NR can reduce hiss by about 10 dB,
DOLBY C NR can achieve a noise reduction of about
20 dB.
This figure represents a three-fold improvement over
DOLBY B NR.
DOLBY C NR also includes an anti-overload circuit and
features controlled high frequency fall-off (spectral
skewing).
These circuits provide a considerable improvement in the
dynamic range of the medium and high frequencies
Note:
The DOLBY B/C noise reduction system only works
correctly if the same noise reduction system is selected
for recording and for playback.
If noise reduction is used for recording or playback only,
then the sound will have an unnatural quality.
The same applies if one noise reduction system is used
for recording and a different one for playback.
The CC 820 M features the DOLBY HX PRO headroom
extension. This system is applied automatically during
the recording process, and does not have to be switched
on manually.
The HX PRO system works with all types of tape
(normal, CrO2 and metal tape).
The DOLBY HX PRO headroom extension works by
raising the tape saturation level in the high frequency
range when a tape recording is made. The result is that
virtually all the high frequency signals, which are often
distorted or lost entirely with a conventional cassette
recorder, are reproduced faithfully by the CC 820 M.
No decoding process is required when a tape recorded
using DOLBY HX PRO is played back, with the result
that the improvement in sound brought about by this
system is apparent when the tape is played back on
other devices (portable cassette recorders or in-car
stereo systems).
HX PRO functions independently of the DOLBY B/C
noise reduction systems, and works whether they are
switched on or off.
Manufactured under licence to Dolby Laboratories.
HX Pro headroom expansion is based on a Bang und
Olufsen development.
„Dolby“, „HX Pro“ and
the double-D symbol are
trademarks of Dolby Laboratories Licensing Corporation.