Voice track
Referenced in the final revised draft of the script for the  first season episode , a voice track was a way to graph a person's voice. It could be displayed on a piece of paper.

In the script, Captain Kirk was about to show Spock a slip of paper that showed a voice track of Kodos, while trying to ascertain whether Kodos was actually now Anton Karidian, when the noise of a phaser on overload suddenly interrupted Kirk and Spock. In the final version of the episode, however, Kirk simply begins to say that he has an idea which may prove Karidian innocent, though Kirk is abruptly silenced by Spock.

See also 
Voice-O-Graph projection
Unused production material