High fidelity or hi-fi reproduction is a term used by home stereo listeners and home audio enthusiasts (audiophiles) to refer to high-quality reproduction of sound or images that are very faithful to the original performance. Ideally, high-fidelity equipment has minimal amounts of noise and distortion and an accurate frequency response as set out in 1973 by the German Deutsches Institut für Normung (DIN) standard DIN 45500. This standard was well intentioned, but only mildly successful in defining 'high-fidelity'. DIN 45 500 approval provided audio equipment buyers with reassurance that their equipment was capable of good quality reproduction. In theory, only stereo equipment that met the standard could bear the words 'hi-fi', but in practice, the term was widely misapplied to audio products that did not remotely approach the DIN basis specifications. By the 1990s, the term hi-fi for expensive high-quality home-audio electronics was largely replaced with high-end audio.

History

The 1920s saw the introduction of electronic amplification, microphones, and the application of quantitative engineering principles to the reproduction of sound. Much of the pioneering work was done at Bell Laboratories and commercialized by Western Electric. Acoustically-recorded disc records with capriciously peaky frequency response were replaced with electrically recorded records. The Victor Orthophonic phonograph, although purely acoustic, was created by engineers who applied waveguide technology to the design of the interior folded horn to produce a smooth frequency response which complemented and equalled that of the electrically recorded Victor Orthophonic records.

Meanwhile, the rise of radio meant increased popularity for loudspeakers and tube amplifiers, so there was an anomaly of a period of time during which radio receivers commonly used loudspeakers and electronic amplifiers to produce sound, while phonographs were still commonly purely mechanical and acoustic. Later, electronic phonographs became available, as stand-alone units or designed to play through consumer's radios. The now ubiquitous RCA connector was first introduced by the Radio Corporation of America for this purpose.

The development of Sound film in the 1930s led motion picture companies to develop amplification and loudspeaker systems to fill movie theaters with good quality sound at a reasonable volume. To achieve this result, they employed loudspeakers with separate sections for low and high frequencies ("woofers" and "tweeters"), connected via an audio crossover network, and more carefully engineered enclosures. This development exposed the public to better fidelity than home equipment was capable of at the time. Some movie stars purchased movie theater sound equipment for use in their homes but the cost and size put them out of reach for anyone of modest means.

After World War II, several innovations created the conditions for a major improvement of home-audio quality: