1979 AKAI CS702DII is a stereo cassette deck with Dolby B noise

Dolby B Noise Reduction. TEAC AN80 Dolby B Noise Reduction unit JRGELECTRONICS Then the inverse of this process is applied on playback, lowering the tape noise in the process. It provides about 10 dB of noise reduction in the high frequencies

The way Dolby B works is to boost high-frequency, low-level signals during the record process, so they are at a higher magnetic level on the tape Dolby B tapes generally sound OK played back without Dolby, sometimes a little bright, which is why it became ubiquitous on prerecorded cassettes

What are the Different Dolby Noise Reduction Systems?

Dolby B sound dull when played back with Dolby B; this is because they are accustomed to the boosted high frequencies they hear when playing these tapes without Dolby A Dolby noise-reduction system, or Dolby NR, is one of a series of noise reduction systems developed by Dolby Laboratories for use in analog audio tape recording This employed 10 bands altogether, some operating at fixed frequencies and others moving automatically to suit the material, and allowed the user to achieve a signal-to-noise ratio of around 90dB from analogue.

Dolby’s Noise Reduction System National Museum of American History. In the professional market, Dolby A was superseded by Dolby SR, which was Dolby's most sophisticated multi-band noise reduction system This increases the noise reduction effect available at frequencies below those occurring in the music signal

Dolby Noise Reduction Processor IC Engineering Projects. This employed 10 bands altogether, some operating at fixed frequencies and others moving automatically to suit the material, and allowed the user to achieve a signal-to-noise ratio of around 90dB from analogue. Played back with Dolby engaged, you get noise reduction.