High fidelity
From Wikipedia, the free encyclopedia
 |
This article may contain original research. Please improve it by verifying the claims made and adding references. Statements consisting only of original research may be removed. More details may be available on the talk page. (July 2009) |
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.[1] 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.
Contents |
[edit] 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 ones. The Victor Orthophonic phonograph, although entirely 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 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:
- Reel-to-reel audio tape recording, based on technology found in Germany after the war, helped musical artists such as Bing Crosby make and distribute recordings with better fidelity.
- The advent of the 33⅓ RPM Long Play (LP) microgroove vinyl record, with low surface noise and quantitatively-specified equalization curves. Classical music fans, who were opinion leaders in the audio market, quickly adopted LPs because, unlike with older records, most classical works would fit on a single LP.
- FM radio, with wider audio bandwidth and less susceptibility to signal interference and fading than AM radio, though AM could be heard at longer distances at night.
- Better amplifier designs, with more attention to frequency response and much higher power output capability, allowing audio peaks to be reproduced without distortion.
In the 1950s, the term high fidelity began to be used by audio manufacturers as a marketing term to describe records and equipment which were intended to provide faithful sound reproduction. While some consumers simply interpreted high fidelity as fancy and expensive equipment, many found the difference in quality between "hi-fi" and the then standard AM radios and 78 RPM records readily apparent and bought 33 LPs, such as RCA's New Orthophonics and London's ffrrs, and high-fidelity phonographs. Audiophiles paid attention to technical characteristics and bought individual components, such as separate turntables, radio tuners, preamplifiers, power amplifiers and loudspeakers. Some enthusiasts assembled their own loudspeaker systems. In the 1950s, hi-fi became a generic term, to some extent displacing phonograph and record player.
In the late 1950s and early 1960s, the development of the Westrex single-groove stereophonic record cutting lathe led to the next wave of home-audio improvement, and in common parlance, stereo displaced hi-fi. Records were now played on a stereo. In the world of the audiophile, however, high fidelity continued and continues to refer to the goal of highly-accurate sound reproduction and to the technological resources available for approaching that goal. This period is most widely regarded as "The Golden Age of Hi-Fi", when tube equipment manufacturers of the time produced many models considered endearing by modern audiophiles, and just before solid state equipment was introduced to the market, subsequently replacing tube equipment as mainstream.
A very popular type of system for reproducing music from the 1970s onwards was the integrated music centre which combined phonograph, radio tuner, tape player, preamp and power amplifier in one package, often sold with its own separate, detachable or integrated speakers. These systems advertised their simplicity; the consumer did not have to select and assemble the individual components. Purists generally avoid referring to these systems as high fidelity, though some are capable of very good quality sound reproduction.
[edit] Ascertaining high fidelity: double-blind tests
In a double-blind experiment, neither the individuals nor the researchers know who belongs to the control group and the experimental group. Only after all the data has been recorded (and in some cases, analyzed) do the researchers learn which individuals are which. A commonly-used variant of this test is the ABX test. This involves comparing two known audio sources (A and B) with either one of these when it has been randomly selected (X). There is no way to prove that a certain lossy methodology is transparent. [2] To scientifically prove that a lossy method is not transparent, double-blind tests may be useful.
[edit] Semblance of realism
When high fidelity was limited to monophonic sound reproduction, a realistic approximation to what the listener would experience in a concert hall was limited. The general clarity of the sound, however, was not any less than with stereophonic sound reproduction.[citation needed] Researchers quickly realized that the ideal way to experience music played back on audio equipment was through multiple transmission channels, but the technology was not available at that time. It was, for example, discovered that a realistic representation of the separation between performers in an orchestra from an ideal listening position in the concert hall would require at least three loudspeakers for the front channels.[citation needed] For the reproduction of the reverberation, at least two loudspeakers placed behind or to the sides of the listener were required.[citation needed]
Stereophonic sound provided a partial solution to the problem of creating some semblance of the illusion of live orchestral performers by creating a phantom middle channel when the listener sits exactly in the middle of the two front loudspeakers. When the listener moves slightly to the side, however, this phantom channel disappears or is greatly reduced. An attempt to provide for the reproduction of the reverberation was tried in the 1970s through quadraphonic sound but, again, the technology at that time was insufficient for the task. Consumers did not want to pay the additional costs required in money and space for the marginal improvements in realism. With the rise in popularity of home theatre, however, multi-channel playback systems became affordable, and many consumers were willing to tolerate the six to eight channels required in a home theater. The advances made in signal processors to synthesize an approximation of a good concert hall can now provide a somewhat more realistic illusion of listening in a concert hall.
In addition to spatial realism, the playback of music must be subjectively free from noise to achieve realism. The compact disc (CD) provides about 90 decibels of dynamic range,[3] which is about as much as most people can tolerate in an average living room.[4]
Audio equipment must be able to reproduce frequencies high enough and low enough to be realistic. The human hearing range, for healthy young persons, is 20 Hz to 20,000 Hz. [5] Most adults can't hear higher than 15 kHz.[3] CDs are capable of reproducing frequencies as low as 10 Hz and as high as 22.05 kHz, making them adequate, in range, to reproduce the frequencies that most people can hear.[3]
The equipment must also provide no noticeable distortion of the signal or emphasis or de-emphasis of any frequency in this frequency range. Except for spatial realism, good modern equipment can easily satisfy all of these requirements at a relatively moderate cost.[citation needed]
[edit] Modularity
Integrated, midi, or lifestyle systems, also known as music centres or minisystems, contain one or more sources such as a CD player, a tuner, or a cassette deck together with a preamplifier and a power amplifier in one box (where Midi has no connection with MIDI technology in electronic instruments). Such products are generally disparaged by audiophiles, although some high-end manufacturers do produce integrated systems. The traditional hi-fi enthusiast, however, will build a system from separates, often with each item from a different manufacturer specialising in a particular component. This provides the most flexibility for piece-by-piece upgrades.
For slightly less flexibility in upgrades, a preamplifier and a power amplifier in one box is called an integrated amplifier; with a tuner, it is a receiver. A monophonic power amplifier, which is called a monoblock, is often used for powering a subwoofer. Other modules in the system may include components like cartridges, tonearms, turntables, Digital Media Players, digital audio players, DVD players that play a wide variety of discs including CDs, CD recorders, MiniDisc recorders, hi-fi videocassette recorders (VCRs) and reel-to-reel tape recorders. Signal modification equipment can include equalizers and signal processors.
This modularity allows the enthusiast to spend as little or as much as he wants on a component that suits his specific needs. In a system built from separates, sometimes a failure on one component still allows partial use of the rest of the system. A repair of an integrated system, though, means complete lack of use of the system.
Another advantage of modularity is the ability to spend one's money on only a few core components at first and then later add additional components to one's system. Because of all these advantages to the modular way of building a high-fidelity system instead of buying an integrated system, audiophiles almost always assemble their system from separates.[citation needed] Some of the disadvantages of this approach are increased cost, complexity, and space required for the components.
[edit] Modern equipment
Modern hi-fi equipment can include signal sources such as digital audio tape (DAT), digital audio broadcasting (DAB) or HD Radio tuners. Some modern hi-fi equipment can be digitally connected using fibre optic TOSLINK cables, universal serial bus (USB) ports (including one to play digital audio files), or WiFi support.
Another modern component is the music server consisting of one or more computer hard drives that hold music in the form of computer files. When the music is stored in an audio file format that is lossless such as FLAC, Monkey's Audio or WMA Lossless, the computer playback of recorded audio can serve as an audiophile-quality source for a hi-fi system.
[edit] See also
[edit] References
- ^ Hartley, H. A.. "High fidelity" (PDF). Audio Design Handbook. New York, New York: Gernsback Library. p. 200. Library of Congress Catalog Card No. 57-9007. http://www.tech-systems-labs.com/books/hartley.pdf. Retrieved 2009-08-08. "I invented the phrase "high fidelity" in 1927 to denote a type of sound reproduction that might be taken rather seriously by a music lover. In those days the average radio or phonograph equipment sounded pretty horrible but, as I was really interested in music, it occurred to me that something might be done about it."
- ^ Spanos, Aris (1999). Probability Theory and Statistical Inference. Cambridge University Press. p. 699. ISBN 0521424089.
- ^ a b c Fries, Bruce; Marty Fries (2005). Digital Audio Essentials. O'Reilly Media. pp. 144–147. ISBN 0596008562. http://books.google.com/books?id=w0vsd5z2Rg4C&pg=PA147. "Digital audio at 16-bit resolution has a theoretical dynamic range of 96 dB, but the actual dynamic range is usually lower because of overhead from filters that are built into most audio systems." ... "Audio CDs achieve about a 90-dB signal-to-noise ratio." "Most adults can't hear frequencies higher than 15 kHz, so the 44.1 kHz sampling rate of CD audio is more than adequate to reproduce the highest frequencies most people can hear."
- ^ Olson, Harry F. (1967) Music, Physics and Engineering, second edition, page 399. Courier Dover Publications, ISBN 0486217698. "...peak sound-pressure levels of sound reproduction in the homes of consumers run from 70 to 90 decibels for 90 per cent of the listeners. The average listener in the home operates a sound-reproducing system at a peak sound-pressure level of 80 decibels."
- ^ D'Ambrose, Chris (2003). "Frequency Range of Human Hearing". The Physics Factbook. http://hypertextbook.com/facts/2003/ChrisDAmbrose.shtml. Retrieved October 11, 2009.
[edit] External links
|
||||||||||||||||||||||||||
