When we came to develop version 3 of the Pro-Codec (and introduce the Pro-Codec Manager) we were advised by Fraunhofer that the MP3-HD codec is obsolete, and so we removed it from the updated version.

MP3-HD is still available in previous versions of the plug-in on a suitable host machine/DAW. The legacy installers (for Pro-Codec v2) are provided from the download link in your Order Confirmation email, or from www.sonnox.com/mysonnox.