HDCD
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| Media type | Optical disc |
|---|---|
| Capacity | Typically up to 700 MB |
| Read mechanism | 780 nm wavelength semiconductor laser |
| Developed by | Pacific Microsonics Inc./Microsoft |
| Usage | Audio storage |
| Extended from | Redbook |
High Definition Compatible Digital, or HDCD is a Microsoft proprietary audio encode-decode process that claims to provide increased dynamic range over that of standard Redbook audio CDs, while retaining backward compatibility with existing Compact disc players.
Originally developed by Pacific Microsonics, the first HDCD-enabled CD was released in 1995. In 2000, the technology was purchased by Microsoft, and the following year, there were over 5,000 HDCD titles available. Microsoft's HDCD official website was discontinued in 2005; by 2008, the number of available titles had declined to around 4,000.
A number of CD and DVD players include HDCD decoding, and versions 9 and above of the Microsoft's Windows Media Player software on personal computers are capable of decoding HDCD.
HDCD encodes the equivalent of 20 bits worth of data in a 16-bit digital audio signal by using custom dithering, audio filters, and some reversible amplitude and gain encoding; Peak Extend, which is a reversible soft limiter and Low Level Range Extend, which is a reversible gain on low-level signals. There is thus a benefit at the expense of a very minor increase in noise.
The claim that the encoding process is compatible with ordinary CD players (without audible distortion), is disputed: “Not being able to decode the peak soft limiting, a normal CD player will output distorted peaks”.
HDCD technology was developed between 1986 and 1991 by "Prof." Keith O. Johnson and Michael "Pflash" Pflaumer of Pacific Microsonics Inc. It was made publicly available as HDCD-enabled audio CDs (often identifiable by the HDCD logo printed on the back cover) in 1995.
In 1998, Burr-Brown (now part of Texas Instruments) and Sanyo Electronics of Japan introduced low cost D-to-A converters with HDCD decoding included, allowing HDCD to be used in CD and DVD players in the $100 range. HDCD algorithms were included in DVD chips from many IC makers including Motorola and C-Cubed, allowing HDCD to be offered by mass-market DVD player makers such as Panasonic and Toshiba.
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