High-resolution audio

High-resolution audio (High-definition audio or HD audio) is a term for audio files 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 (CD-DA), which operates at 44.1 kHz/16-bit.
The Recording Industry Association of America (RIAA), 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 (48 kHz/20-bit or higher) 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 (SACD).
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. These formats offer additional benefits such as multi-channel surround sound. Following a format war, 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 Audio Blu-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 (JEITA) 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:
...and with other opinions ranging from skeptical to highly critical:
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 audio at 48 kHz. One 2014 paper showed that dithering using outdated methods produces audible artifacts in blind listening tests.
A 2007 study showed no audio difference between CD quality audio and higher resolution audio. Joshua Reiss performed a meta-analysis on 20 of published tests, saying that trained listeners could distinguish between hi-resolution recordings and their CD equivalents under blind conditions. Hiroshi Nittono pointed out that the results in Reiss's paper showed that the ability to distinguish hi resolution audio from CD quality audio "was only slightly better than chance".