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
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superseded by newer and more sophisticated digital audio technologies such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.
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
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
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.
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 -
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'
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