Spellsinger is the title of the first book in the series of the same name, by Alan Dean Foster. The books feature a young pre-law student by the name of Jonathan Thomas Meriweather, who wishes to be a rock musician despite a distinct lack of singing talent. After a pot-smoking bender, he wakes up in a mysterious alternate universe inhabited by talking animals. Jon-Tom, as he is known there, discovers that he was summoned by the tortoise wizard Clothahump to assist in the fight against the evil insects of the Greendowns, and manifests the powers of a "spellsinger."
Spellsinging is the ability to work magic via singing and playing an instrument simultaneously, but the song must be chosen carefully or it can have unexpected effects. For example, Jimi Hendrix's "Purple Haze" causes his instrument (a fictional stringed instrument called a duar) to produce a lot of purple smoke, and when he sings most of Def Leppard's album Pyromaniac in an attempt to placate fire spirits, the strings start to glow red hot.