High Definition Compatible Digital
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Image:HDCD.jpg High Definition Compatible Digital, or HDCD (commonly known as High Definition Compact Disc) is a patented encode-decode process that endeavors to improve the audio quality of Red Book audio CDs.
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Overview
HDCD encoding places a control signal in the least significant bit of the 16-bit audio samples (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 (only decreasing the signal-to-noise ratio by a miniscule amount), but depending on what optional features are used (see below), the sound may be distorted in the absence of an HDCD decoder.
Description
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 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 Incorporated. 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 XP's Windows Media Player 9, 10 and likely any future versions include a HDCD decoder. This is currently the only purely software-based HDCD decoder available. (The feature is not available on earlier Windows systems, like Windows 2000.)
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