Vocal subprocessor

From Memory Alpha, the free Star Trek reference.

A vocal subprocessor is a Borg implant placed near the esophageal aperture in the neck of a drone. This implant is designed to facilitate the sonic interface with Borg transponders. It also enables its user to have "perfect pitch" in speech and other forms of communication. (VOY: "Someone to Watch Over Me", "Collective", "Unimatrix Zero, Part II")