High Definition Compatible Digital

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.

Technical overview

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.