IPA: /ɪnˈtoʊnər/
KK: /ɪnˈtoʊnər/
A person or device that produces a musical or vocal tone, often used in singing or speaking.
The intoner skillfully adjusted the pitch of the choir's performance.
Intoner is formed from "in-" (meaning into) and "toner" (from Latin "tonare", meaning to thunder or make a sound). The word refers to someone who brings sound into a performance or speech, often in a musical context.
Think of someone bringing 'sound' ('tonare') into a performance ('in-') — that's what an intoner does.