Voice duplicator
A voice duplicator or voice synthesizer was a mechanism or method for imitating the voice of another individual. Technology of this sort was used chiefly for subterfuge. An individual with a sample of the real voiceprint, a sample of the imitation, and analysis software could sometimes detect the deception. Voice duplicators could be standalone instruments, or they could be incorporated into more complex machinery.

In 2266, the self-aware android Ruk demonstrated the ability to duplicate the voice of anyone he had heard. He later attempted to deceive James T. Kirk with this ability, speaking as if he were Christine Chapel, but Kirk, having seen it demonstrated, was not fooled. ()

The Gorn possess voice duplicator technology good enough to fool at least an unsuspecting listener. After their attack on Cestus III, they used this technology to trick Kirk into visiting the destroyed colony, and bringing along his tactical specialists. Their goal was to isolate these men so that an emplaced ground force could destroy them quickly. ()

In 2267, Anan 7, then leader of the Eminian Union, used a voice duplicator to imitate Kirk. His goal was to lure the crew of the  to the surface of Eminiar VII so they could be killed in accordance with a treaty he was obligated to enforce. Montgomery Scott, in command of the ship, was able to discover the deception using a computer analysis. ()

In 2364, Wesley Crusher created a device that duplicated the voice of Captain Jean-Luc Picard, which had been captured by Crusher from various instances of his using the ship's intercom. According to Crusher, since he wasn't allowed on the bridge, he could imagine himself there and "pretend he's ordering me to take the Enterprise anywhere." 

Later, while under the influence of polywater intoxication, Crusher was able to use it to get Chief Engineer MacDougal and Assistant Chief Engineer Jim Shimoda outside of the control booth in main engineering. ()

In the 24th century, several artificial lifeforms in service of the Federation had the ability to duplicate voices. In 2367, Lieutenant Commander Data, under the influence of a signal sent from his creator, was able to duplicate the voice of Captain Picard and commandeer the Enterprise-D. () 

In 2372, an operative of the True Way terrorist group used a voice synthesizer to duplicate Worf's voice. He did so in order to trick Odo into releasing control of a turbolift to him so he could use it in an attempt to assassinate Shakaar Edon. ()

The Emergency Medical Hologram was also capable of duplicating voices. ()

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