I've been suffering from excessive slowness in Melodyne startup since I upgraded to v4 (from v3) several years ago: the first instantiation per run of Cakewalk/SONAR before it, or even a VST scan, would take almost exactly 15 seconds (on old quad core Q6600 as well as more recent Ruzen 2600).  Subsequent opens in the same Cakewalk/SONAR session were fast. Celemony support were unable to help. Thanks to a post on an unrelated topic in this forum: I can confirm that the lack of iLo