From Just Solve the File Format Problem
RK Audio is a proprietary lossless audio format created by RK Software (later M Software) and is a variant of the RK compression format. It does not appear to be supported by WinRK, the successor to RK.
- RK Software - RK Audio page (Wayback Machine capture 2005-02-07)
- Info for RKAU files. A patch for MediaInfo adding support for RK Audio files.