High Definition Compatible Digital or HDCD

is a patented encode-decode process that claims to improve the sound quality of standard audio CDs.

An 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 improved dynamic range that a decoded HDCD can deliver relative to standard 16-bit linear PCM " Red Book " CD recordings.

HDCD encoded CDs may be played back on systems without HDCD decoding with acceptable audio quality.

At ~4000 titles HDCD encoded releases are a relatively small fraction of the total CD commercial music catalog, and only fraction of the players that have been sold are capable of decoding them.

Some universal CD/DVD media players include HDCD decoding and 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, audiophiles now have the option of seeking higher resolution digital recordings on newer and more sophisticated digital audio formats based on higher bit rate media such as Super Audio CD (SACD) and DVD-Audio.

-- From Wikipedia --