A pity, but if one wanted to play back commercial tapes, Dolby B was usually the only option.
Most of my friends were using Dolby C for their mix tapes and radio show recordings.
I do not know anyone that bought more than 2 or 3 commercial tapes.
They bought the albums & then recorded those to use as their tapes in the garage or backyard (or the occasional mixed tape for their love "significant other" that they would enjoy on a date in the car at lover's lane (or in my crowds use case, in the boat while water skiing).
As a result of the extra signal processing, Dolby C-type recordings will sound distorted when played back on equipment that does not have the required Dolby C decoding circuitry.
Some of this harshness can be mitigated by using Dolby B on playback, which serves to reduce the strength of the high frequencies.
Dolby C first appeared on higher-end cassette decks in the 1980s. The first commercially available cassette deck with Dolby C was the
NAD 6150C, which came onto the market around 1981. Dolby C was also used on professional video equipment for the audio tracks of the
Betacam and
Umatic SP videocassette formats. In Japan, the first cassette deck with Dolby C was the AD-FF5 from
Aiwa. Cassette decks with Dolby C also included Dolby B for backward compatibility, and were usually labeled as having "Dolby B-C NR".
Dolby HX/HX-Pro[edit]
Further information:
Adaptive biasing
The Dolby HX circuitry driven by the industry-standard NEC uPC1297 integrated circuit. It modulates the incoming bias current and injects it into the two channels of the stereo recording head via two ferrite transformers.
Magnetic tape is inherently non-linear in nature due to
hysteresis of the magnetic material. If an
analog signal were recorded directly onto magnetic tape, its reproduction would be extremely distorted due to this
non-linearity. To overcome this, a high-frequency signal, known as bias, is mixed in with the recorded signal, which "pushes" the envelope of the signal into the linear region. If the audio signal contains strong high-frequency content (in particular from percussion instruments such as
hi-hat cymbals), this adds to the constant bias causing magnetic saturation on the tape. Dynamic, or adaptive, biasing automatically reduces the bias signal in the presence of strong high-frequency signals, making it possible to record at a higher signal level.
The original Dolby HX, where
HX stands for
Headroom eXtension, was invented in 1979 by Kenneth Gundry of Dolby Laboratories, and was rejected by the industry for its inherent flaws.
Bang & Olufsen continued work in the same direction, which resulted in a 1981 patent (EP 0046410) by Jørgen Selmer Jensen.
[22] Bang & Olufsen immediately licensed HX-Pro to Dolby Laboratories, stipulating a priority period of several years for use in consumer products, to protect their own Beocord 9000 cassette tape deck.
[23][24] By the middle of the 1980s the Bang & Olufsen system, marketed through Dolby Laboratories, became an industry standard under the name of Dolby HX Pro.
HX-Pro only applies during the recording process. The improved signal-to-noise ratio is available no matter which tape deck the tape is played back on, and therefore HX-Pro is not a noise-reduction system in the same way as Dolby A, B, C, and S, although it does help to improve noise reduction encode/decode tracking accuracy by reducing tape non-linearity. Some record companies issued HX-Pro pre-recorded cassette tapes during the late 1980s and early 1990s.
The Dolby HX circuitry driven by the industry-standard NEC uPC1297 integrated circuit. It modulates the incoming bias current and injects it into the two channels of the stereo recording head via two ferrite transformers.
