Every analogue tape recording carries a constant, breathy background noise, most noticeable in the treble and in quiet passages, and especially familiar from cassettes. Noise-reduction systems were developed to fight it: Dolby Laboratories, founded by Ray Dolby in 1965, boosted high frequencies during recording and reduced them again on playback, pushing the hiss down with them.
In lo-fi music, hiss has become an aesthetic rather than a defect. Adam Scott Neal notes that 1990s alternative rock already used tape hiss and similar noise as part of a lo-fi sound. Producers today record parts onto cassette or add hiss with plug-ins to suggest a home recording, a mixtape or a worn copy. In jazz lo-fi it usually sits very low, a faint layer of air alongside vinyl crackle that makes a digital track feel intimate and handmade.