Operating instructions

D-4
Dolby B-type was the first Dolby system developed for consumer applications,
and is in use today in hundreds of millions of cassette recorders and other
products (a modified version of B-type noise reduction is also used to encode
the surround channel on Dolby Stereo and Dolby Stereo SR release prints).
Dolby C-type was later developed to provide more noise reduction than Dolby
B-type, and is provided along with B-type in many of today’s high-performance
consumer products. The newest consumer system, Dolby S-type, is based on
some of the operating principles of DolbySR, and provides still more noise
reduction. In addition, much like DolbySR on film soundtracks, S-type also
improves a cassette recorder’s high-level signal capability. The result on the
newest decks with Dolby S-type is cassette performance subjectively equivalent
to the Compact Disc.
These consumer systems systems differ from the professional Dolby systems in
the type of noise reduction they achieve. Because they were developed for
professional applications, Dolby A-type and DolbySR reduce all types of noise
at all frequencies (low-frequency hum as well as high-frequency hiss). The
Dolby B-type and C-type reduce the tape hiss which prevails in cassette
recording; the circuits are considerably simpler and operate primarily at the
higher hiss-related frequencies. Dolby S-type provides even more hiss reduction,
and some noise reduction at low-frequencies as well.