High-resolution audio is a technical and marketing term for audio with greater than 44.1 kHz sample rate or higher than 16-bit audio bit depth. It commonly refers to 96 or 192 kHz sample rates. However, there also exist 44.1 kHz/24-bit, 48 kHz/24-bit and 88.2 kHz/24-bit recordings that are labeled HD Audio. Research into high resolution audio began in the late 1980s and high resolution audio content started to become available on the consumer market in 1996.
Definitions
High-resolution audio is generally used to refer to music files that have a higher sampling frequency and/or bit depth than that of Compact Disc Digital Audio, which operates at 44.1 kHz/16-bit. The Recording Industry Association of America, in cooperation with the Consumer Electronics Association, DEG: The Digital Entertainment Group, and The Recording Academy Producers & Engineers Wing, formulated the following definition of high-resolution audio in 2014: "lossless audio capable of reproducing the full spectrum of sound from recordings which have been mastered from better than CD quality music sources which represent what the artists, producers and engineers originally intended." File formats capable of storing high-resolution audio include FLAC, ALAC, WAV, AIFF and DSD, the format used by Super Audio Compact Discs.
History
One of the first attempts to market high-resolution audio was High Definition Compatible Digital in 1995. This was followed by three more optical disc formats claiming sonic superiority over CD-DA: DAD in 1998, SACD in 1999, and DVD-Audio in 2000. None of these achieved widespread adoption. Following the rise in online music retailing at the start of the 21st century, high-resolution audio downloads were introduced by HDtracks starting in 2008. Further attempts to market high-resolution audio on optical disc followed with Pure AudioBlu-ray in 2009, and High Fidelity Pure Audio in 2013. Competition in online high-resolution audio retail stepped-up in 2014 with the announcement of Neil Young's Pono service. In 2014 the Japan Electronics and Information Technology Industries Association announced a specification and accompanying "Hi-Res AUDIO" logo for consumer audio products. Sony reaffirmed its commitment towards the development in the high-resolution audio segment by offering a slew of Hi-Res Audio products.
Controversy
Whether there is any benefit to high-resolution audio over CD-DA is controversial, with some sources claiming sonic superiority:
"The DSD process used for producing SACDs captures more of the nuances from a performance and reproduces them with a clarity and transparency not possible with CD.—The Mariinsky record label of the Mariinsky Ballet, St. Petersburg, Russia, that sells Super Audio CDs
"the main claimed benefit of high-resolution audio files is superior sound quality 24-bit/96 kHz or 24-bit/192 kHz files should, therefore, more closely replicate the sound quality that the musicians and engineers were working with in the studio."—What Hi-Fi?
and with other opinions ranging from skeptical to highly critical:
"If they cared about sound quality in the first place, they would make all of the releases sound great in every format they sell: MP3, FLAC, CD, iTunes, or LP."—cnet
"Impractical overkill that nobody can afford"—Gizmodo
Business magazine Bloomberg Businessweek suggests that caution is in order with regard to high-resolution audio: "There is reason to be wary, given consumer electronics companies' history of pushing advancements whose main virtue is to require everyone to buy new gadgets." High-resolution files that are downloaded from niche websites that cater to audiophile listeners often include different mastering in the release thus many comparisons of CD to these releases are evaluating differences in mastering, rather than bit depth. Most early papers using blind listening tests concluded that differences are not audible by the sample of listeners taking the test. Blind tests have shown that musicians and composers are unable to distinguish higher resolutions from 16-bit/48 kHz One 2014 paper showed that dithering using outdated methods produces audible artifacts in blind listening tests. Since the Meyer-Moran study in 2007, approximately 80 studies have been published on high-resolution audio, about half of which included blind tests. Dr. Joshua Reiss, of the Queen Mary University of London, and a member of the Audio Engineering SocietyBoard of Governors, performed a meta-analysis on 20 of the published tests that included sufficient experimental detail and data. In a paper published in the July 2016 issue of the AES Journal, Dr. Reiss says that, although the individual tests had mixed results, and that the effect was "perhaps small and difficult to detect," the overall result was that trained listeners could distinguish between hi-resolution recordings and their CD equivalents under blind conditions: "Overall, there was a small but statistically significant ability to discriminate between standard quality audio and high resolution audio. When subjects were trained, the ability to discriminate was far more significant."
