Dolby HX

Invented by Bang & Olufsen and licensed to Dolby. HX (often marketed as HX Pro) stands for 'Headroom eXtension' and it is a record-processing system used on some analogue open-reel and cassette tape-recorders (there is no complementary replay processing). Dolby HX Pro varies the amount of recording bias depending on the strength of high-frequencies in the audio signal itself to avoid magnetic saturation and over-biasing. This makes it possible to record with a higher overall fluxivity on the tape.