High-resolution audio

High-resolution audio, also known as High-definition audio or HD audio, is a marketing term used by some recorded-music retailers and high-fidelity sound reproduction equipment vendors.^[1][2] It refers to higher than 44.1 kHz sample rate and/or higher that 16-bit linear bit depth. It usually means 96 kHz (or even much higher), sometimes informally written as "96k", meaning a Nyquist frequency of 48KHz, which is outside of the hearing range of any human ear.

Definitions

Approximate dynamic range and bandwidths of some high-resolution audio formats

There is no standard definition for what constitutes high-resolution audio,^[3] but it is generally used to describe audio signals with bandwidth and/or dynamic range greater than that of Compact Disc Digital Audio (CD-DA, informally CDs).^[2] This includes pulse-code modulation (PCM) encoded audio with sampling rates greater than 44,100 Hz and with bit-depths greater than 16,^[2] or their equivalents using other encoding techniques such as pulse-density modulation (PDM).^[3]

Although there is no firm definition, Sony describes high-resolution audio devices as those that deliver audio that’s clearer, sharper and more complex than other music sources and closer to the original.^[4]

File formats capable of storing high-resolution audio include FLAC, ALAC, WAV, AIFF and DSD, the format used by Super Audio Compact Discs (SACD).^[3]

History

One of the first attempts to market high-resolution audio was High Definition Compatible Digital in 1995.^[5] 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.^[6]

Following the rise in online music retailing at the start of the 21st century, high-resolution audio downloads were introduced by HDtracks^[6] 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.^[7] Competition in online high-resolution audio retail stepped-up in 2014 with the announcement of Neil Young's Pono service.^[8]

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.^[9]—The Mariinsky record label of the Mariinsky Ballet (formerly Kirov Ballet), St. Petersburg, Russia, that sells Super Audio CDs (SACDs)
• "the main claimed benefit of high-resolution audio files is superior sound quality [..] 24-bit/96k or 24-bit/192kHz files should therefore more closely replicate the sound quality that the musicians and engineers were working with in the studio. [..] As always, though, there are some people who can't hear a difference. So, if you can't see or hear a difference, save your money…"—What Hi-Fi?^[3]

and with other opinions ranging from skeptical to highly critical:

• "If they [the music business] 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^[10]
• "Impractical overkill that nobody can afford"—Gizmodo^[2]
• "A solution to a problem that doesn't exist, a business model based on wilful ignorance and scamming people."—Xiph.org^[11]

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."^[12]

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 "special" releases are evaluating differences in mastering, rather than bit depth.^[13]

In the early days of Super Audio CD, a number of special remastered releases were published, and consumers expressed a preference for the SACD remasters. A scientific double blind trial, however, showed that by professionally producing a CD from the SACD master, individuals could not detect a difference in an ABX test.^[11] Notably, many people who perform their own unblinded listening tests do not match the decibel level of both audio sources, or guarantee that the CD version is produced from the high resolution version (to guarantee no mastering differences).^[11]

Most early papers using blind listening tests concluded that differences are not audible by the sample of listeners taking the test.^[14] Blind tests have shown that musicians and composers are unable to distinguish higher resolutions from 16-bits 48 kHz^[15] One 2014 paper showed that dithering using outdated methods (rectangular unshaped dither, rather than the industry standard triangular dither) produces audible artifacts in blind listening tests.^[16]

Notes