Shrillness enotes the harsh, strident quality a sound has. Some instruments, like the piccolo have a shrillness in the upper register; thus notes there are mostly used for ornamentation. In the human voice, shrillness relates to the degree in which a vocal sounds like a scream. Although any pitch, high or low, can be shrill, the terminology usually is applied to sounds high in the whistle register, where the difference between a musical note and a blood curdling scream can be thin.