HDCD

Keith Johnson and Michael Pflaumer at Pacific Microsonics wanted more than 16 bits out of a format that didn't allow it. HDCD tucks a hidden code stream into the lowest bit, sparse and pseudo-random, carrying instructions for peak extension and low-level gain. An ordinary CD player plays the disc as is; a decoder was claimed to deliver up to 20 bits of resolution.

The outcome was odd. Thousands of discs carried the HDCD flag, often simply because the mastering house used Pacific Microsonics converters, while most listeners never owned a decoder. Microsoft bought the technology in 2000 and built decoding into Windows Media Player — and then things went quiet. A format for sneaking extra bits past CD-DA became redundant once hi-res audio could be delivered directly.