High Definition Compatible Digital, or HDCD is a patented encode-decode process, now under Microsoft, that improves the audio quality of standard Redbook audio CDs, while retaining backward compatibility with existing Compact disc players.

At over 4000 titles, HDCD-encoded releases constitute a fraction of the total CD commercial music catalog, but many popular artists insist on using HDCD for their new releases. A web site devoted to HDCD recordings can be found at the following location ].

A number of universal CD and DVD players include HDCD decoding, and version 9 and above of the Windows Media Player software (on personal computers with a 24-bit sound card) are capable of decoding HDCD.

An HDCD-encoded CD usually, but not always, has the HDCD logo printed on the back cover. An HDCD logo will be displayed in Windows Media Player 9 or above when an HDCD encoded disc is played.

New HDCD-encoded CDs are still being mastered and being added to various catalogs, and there is no extra cost for these HDCD recordings, unlike the higher price charged for newer digital audio formats based on higher bit-rate media such as Super Audio CD (SACD) and DVD-Audio.

Technical overview

HDCD encodes the equivalent of 20 bits worth of data in a 16-bit digital audio signal by utilizing custom dithering, audio filters, and some reversible amplitude and gain encoding; Peak Extend, which is a reversible soft limiter and Low Level Range Extend, which is a reversible gain on low-level signals.

HDCD encoding places a control signal in the least significant bit of the 16-bit Red Book audio samples (a technique known as in-band signaling). The HDCD decoder in the consumer's CD or DVD player, if present, responds to the signal. If no decoder is present, the disc will be played as a regular CD.

In itself, the use of the first bit in the dithered least significant bit stream does not degrade the sound quality on a non-HDCD player; it only decreases the signal-to-noise ratio by a minuscule amount. HDCD Peak Extension, if chosen in HDCD mastering, will apply compression to the peaks which will be audible in playback on a non-HDCD system which does not apply the approriate expansion curve.

HDCD provides several digital features, which the audio mastering engineer controls at his/her own discretion. They include:

Dynamic range compression and expansion, with which virtually 4 more bits of accuracy can be added to the musical signal.

Precision digital interpolation filtering with multiple modes of operation, that can reduce alias distortion and temporal smearing, resulting in a more natural, open, and accurate sound reproduction.

History

HDCD technology was developed between 1986 and 1991 by Keith Johnson and Michael "Pflash" Pflaumer of Pacific Microsonics Inc. It was made publicly available as HDCD-enabled audio CDs in 1995.

In 2000, Microsoft acquired the company and all of its intellectual property assets.

There have been a number of players and processors over the years that were capable of properly decoding the information from HDCDs. Included were those from California Audio Labs (USA), Mark Levinson/Madrigal (USA), Cary (USA), Naim (England), Linn (Scotland), Classe (Canada), A&R Cambridge Ltd (ARCAM) (England), Rotel (Japan) and Cayin-Spark (China). Outboard DACs (digital to analog converters) were produced by Manley Labs, Classe, Mark Levinson and others. Manley Labs also made a unique component called "the Wave," which was a tube-based preamplifier that featured digital inputs for HDCD processing.

In 1998 Burr-Brown (now part of Texas Instruments) and Sanyo Electronics of Japan introduced low cost D to A converters with HDCD decoding included, allowing HDCD to be used in CD and DVD players in the $100 range. HDCD algorithms were included in DVD chips from many IC makers including Motorola and C-Cubed, allowing HDCD to be offered by mass-market DVD player makers such as Panasonic. As of 2007, a number of players continue to feature HDCD capability, including Denon, Marantz, Cary, Rotel, Mark Levinson, Shanling, and NAD.

There are no labels that record and release only HDCDs. Reference Recordings has produced many classical CDs in the HDCD format, which include new releases and have won numerous awards. Linn Recordings has a number of hybrid HDCD / SACDs, and also seem to enjoy a good reputation amongst music enthusiasts.

As far as "mainstream" popular artists, The Grateful Dead, Jerry Garcia, Mark Knopfler, King Crimson, Van Halen, Joni Mitchell, Neil Young and Mike Oldfield have quite a few of their albums that have been released on HDCDs. As of January 2007, there are roughly the same number of titles released on SACDs as there are on HDCDs (4000 or so at last count).

Windows Media Player

Windows Media Player 9, 10 or 11 running on Windows XP and Windows Media Player 11 running on Windows Vista are all capable of decoding and playing HDCDs on personal computers with a 24-bit sound card installed. This is currently the only purely software-based HDCD decoder available.

This feature must be enabled by changing a "Properties" setting of the Speakers involving 24-bit audio. The path to this setting is:Tools - Options - Devices - Speakers - Properties - Performance