High Definition Compatible Digital, or HDCD (also known as High Definition Compact Disc) is a patented encode-decode process that endeavors 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 is required in order to take advantage of the subtle improvement that HDCD is intended to accomplish.

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 Although new HDCD-encoded CDs are still occasionally added to various catalogs, the format has been largely superseded by newer and more sophisticated digital audio technologies such as Super Audio CD (SACD) and DVD-Audio.

Technical overview

HDCD is a proprietary process, and no accurate technical description has been released to the public. Hence, the following known attributes are somewhat general, i.e. not verbose or technically in-depth.

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.

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.

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. 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

Note that although 24-bit audio output is enabled, decoded HDCD is still a 20-bit standard. Because sound cards are typically set at 16 or 24 bits, it is necessary to 'step up' to 24 bits before the 20-bit HDCD output can be used.

Wikipedia information about High Definition Compatible Digital. This article is licensed under the GNU Free Documentation License . It uses material from the Wikipedia article 'High Definition Compatible Digital'