RK Audio (RKAU) is a legacy lossless (and lossy) audio codec for the Windows platform. It was developed by Malcolm Taylor together with RK (a general purpose data compressor) and RKim (a lossless image compressor).
Development apparently ceased around year 2000; the author offered it for download until circa 2005 at his new company MSoftware, which then for a while revived the compression suite (including an audio compressor) as the WinRK archiver, now also discontinued.
Testing by ReallyRareWares and Squeezechart indicated excellent compression level by year 2000 standards, at the cost of high CPU usage. Features were few.
|Lossless||(Uncompressed linear PCM) • ALAC • FLAC • La • MLP/Dolby TrueHD • Monkey's Audio • MPEG-4 ALS/LPAC/LTAC • OptimFROG • RealAudio Lossless • RK Audio • Shorten • TAK • TTA • WavPack • WMA Lossless|
|Lossy||AAC • AC-3 • ADPCM • ATRAC • DTS • MP2 • MP3 • Musepack • Opus • QDesign • Speex • Vorbis • VQF • WMA|
|Hybrid||ATRAC Advanced Lossless • DTS-HD • mp3HD • MPEG-4 SLS • OptimFROG DualStream • WavPack|