From Sonnet Technologies:
Utility that fixes most audio and video playback problems which occur during playback of files from drives attached to an ATA host adapter installed in pre-G3 Power Macintosh and Macintosh clone computers. The AV Optimizer resolves playback issues by slowing down the data transfer between drives attached to the Tempo Ultra ATA66, Tempo RAID66 or Tempo RAID133 and your legacy Macintosh. This utility is only for use with the listed Tempo PCI Host Adapter cards and pre-G3 Power Macintosh and Macintosh clone computers. It is not compatible with any other computer or ATA host adapter card.