Ray Dolby’s 1965 invention of a system for reducing unwanted noise in magnetic tape recording significantly enhanced sound quality in consumer devices. His circuit design compressed and then expanded the electrical signal, a design he called a “sound compander” for which he received U.S. Patent 3,846,719. At first, Dolby’s compander was sold as an add-on component but by the early 1970s, it became an integral part of the equipment. This Advent model 201 cassette deck features a switch to activate Dolby’s system. The recorder also included a switch that allowed the use of chromium oxide tapes. The CrO2 tapes gave superior performance than ordinary ferrite oxide tapes but the sound properties could change over time. The switch helped the Dolby system compensate.
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