High Definition Compatible Digital

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High Definition Compatible Digital, or HDCD is a patented encode-decode process that claims to improve the sound quality of standard audio CDs. A HDCD-encoded CD usually, but not always, has the HDCD logo printed somewhere on the back cover. A relatively high-quality sound-system would be required to take advantage of the purported improvement in bit-depth (or dynamic range) that HDCD is intended to accomplish.

Currently, Microsoft, the owners of HDCD technology, have removed all information about it from their website.

There are a relatively small number of CDs which have been encoded in HDCD, and a correspondingly small number of players have been sold which are capable of decoding them. However version 9 and above of Windows Media Player running on Microsoft Windows XP is capable of decoding HDCD on personal computers with a 24-bit sound card.

HDCD was an early attempt by audiophiles to improve the sound-quality of CDs, while retaining backward compatibility with existing players. Although new HDCD-encoded CDs are still occasionally added to various catalogs, the format has been largely superseded by newer and more sophisticated digital audio technologies such as Super Audio CD (SACD) and DVD-Audio.

1 Technical overview
2 History
3 Windows Media Player
4 External links

[edit] Technical overview

HDCD is a proprietary process, and no accurate technical description has been released to the public. Hence, none of its claims have any evidence. In fact, since the technology does not involve compression, and still allows an audio CD to hold the normal 80 minutes of audio within 700MB, the additional 4 bits of bit depth it claims to add to the seems to be a monumental feat of engineering.

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 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 least significant bit does little to degrade sound quality on a non-HDCD player (only decreasing the signal-to-noise ratio by a minuscule amount).

HDCD provides several digital features, which the audio mastering engineer controls at his/hers 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, which can reduce alias distortion and temporal smearing, resulting in a more natural, open, and accurate sound reproduction.

[edit] 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 cd players and processors over the years that were capable of properly decoding the information from HDCD's. Some of the "higher end" CD players included those from California Audio Labs (USA), Mark Levinson / Madrigal (USA) , Cary (USA), Naim (England) , Linn (Scotland), Classe (Canada), Arcam, and Rotel. Outboard DAC's (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. As of 2007, very few new CD players in the US continue to feature HDCD capability, but they do exist, notably some from Denon. HDCD titles and hardware continue to be made, however they seem to be more popular in Asia than in the West.

A few labels continue to record and release HDCD's. Reference Recordings has many classical CD's done in the HDCD format, which include new releases and have won numerous awards. Linn Recordings has a number of hybrid HDCD / SACD's, and also seem to enjoy a good reputation amongst music enthusiasts. As far as "mainstream" popular artists, Mark Knopfler, Van Halen & Neil Young have quite a few of their albums that have been released on HDCD. Interestingly, as of January 2007, there are roughly the same number of titles released on SACD as there are on HDCD.

[edit] Windows Media Player

Version 9 and above of Windows Media Player running on Microsoft Windows XP is capable of decoding HDCD on personal computers with a 24-bit sound card enabled. [1] [2] 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