Those of you who remember the early 2000s will recall that most of the world was still consuming music on CD. Our family was no exception, and we ended up with a fine CD player that had an interesting feature—it was able to decode regular CDs as well as high-definition-compatible digital (HDCD) discs.
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.
Pacific Microsonics, the manufacturer, ceased operations in 2000.
Fortunately, FFmpeg’s libavfilter includes an HDCD filter as of FFmpeg 3.1 (June 2016) that will convert 16-bit PCM with HDCD data to 20-bit PCM.”
See the article on the Linux commands used to decode the audio and reencode it to flac.
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