High Definition Compatible Digital (HDCD) is a proprietary audio encode-decode process that claims to provide increased dynamic range over that of standard Red Book audio CDs, while retaining backward compatibility with existing compact disc players.

HDCD was a favorite for several artists such as Joni Mitchell, Neil Young and the Beach Boys, all of whom have had many titles in their catalogs reissued in this format.

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.