The vocal folds, groups of muscle tissue in the larynx, are normally open to allow breathing. When you speak they close, while air from the lungs makes them vibrate. This produces sound. The size and shape of the vocal folds and surrounding cavities (throat, mouth and nose) help determine the pitch, volume and tone of your voice. This is what makes it unique. When illness or disease affects your voice, it can change the pitch, volume and quality of sound.