So, I still don't get how this 1966 "black box" worked, but I take Bob Justman at his word that there was indeed some large, clumsy, expensive tehcnology available to have changed the pitch of Malachi Throne's voice--and, off the top of my head, probably Cloud Williams' in "The Omega Glory" and Lt. Mira Romaine's in "The Lights of Zetar."
Cloud William? No, his voice doesn't sound artificially deepened; he's just a natural bass. Heck, Ted Cassidy had a deeper voice than that.
The other major example of pitch changing in TOS would be Professor Crater in "The Man Trap," whose dialogue was slowed or pitched down for a few moments after he was phaser-stunned.
In "The Omega Glory," in scene 155, Cloud William says "The fight is done when one is dead." This same scene appears in the "scenes from next week" trailer. But when this dialog is heard in the scenes from next week, the dialog is noticably higher in pitch than in the actual episode. We notice a pitch change on Professor Crater, of course, because we have two different pitches to compare. We don't really notice it on Cloud WIlliam/Roy Jenson, because we don't have two different pitches to compare--except that, thanks to the preview trailer, we actually do. I think Roy Jenson's dialog was deepened throughout the entire episode--but not in the preview trailer.