 It is basically a cut down version of Dolby "SR" and uses many of the same noise reduction techniques.Dolby "S" is capable of 10 dB of noise reduction at low frequencies and up to 24 dB of noise reduction at high frequencies.Dolby HX-Pro was invented in 1980 and patented in 1981 (EP 0046410) by Jørgen Selmer Jensen of Bang & Olufsen.