Dolby’s Noise Reduction System

Recording on magnetic tape introduced unwanted noise or “hiss” to the sound; the noise only accumulated as the original production tapes were duplicated, then played. In 1965 Ray Dolby invented electronic circuitry that removed unwanted noise by processing the audio signal. Recording studios quickly adopted Dolby’s system, and makers of cassette tape players soon followed.

Dolby A301 prototype audio noise reduction unit

Ray Dolby’s first product, the model A301, used a circuit design that reduced tape noise by compressing and expanding audio signals, 1965

Gift of Dolby Corporation

View object record

Circuit board from the model A301, 1965

Listening on the Move

Cassette tapes were small and easily transported. Small, lightweight cassette players, whether handheld or tucked into fanny packs, were a boon to commuters and joggers. Transistor radios had made music portable in the 1950s, but cassettes let the listener be the deejay by selecting or creating their own “mix” tapes.

In 1984 Sony added a miniaturized version of Ray Dolby’s noise reduction system to its Walkman Pro. The feature soon became widely available; without it, hiss was especially noticeable because listeners’ headphones blocked many distracting sounds.

"Walkman" portable cassette player, Model WM-D6

Meet the 1960s Dolby Noise Reduction Machine

Do you enjoy hiss-free recordings of your favorite music and podcasts? In this video, Hall Wallace, Curator of our Electricity Collections, shows how the Dolby Noise Reduction Machine worked.

View on Youtube!