Distune

[…] the clapper of his distuned belle May cankre soone I mene his false tonge Be doumbe for euer & neuer efte to be runge

Source: wiktionary

And as the Musician neyther streyneth the string of his instrument to hye, for feare of breaking, nor lette[t]h it to low for feare of distuning. So god […] will keepe a meane neyther suffering vs to be carelesselye secure, nor driuing vs for want of comforte to despayre.

Source: wiktionary

[…] thy voice distuned and marred of modulation;

Source: wiktionary

A judicious distuning, applied to piano tone, has the effect of introducing a wavering quality which the ear interprets as a pleasing liveliness of tone.

Source: wiktionary