George Crumb (born October 24, 1929) is an American composer of contemporary classical music. He is noted as an explorer of unusual timbres, alternative forms of notation, and extended instrumental and vocal techniques. Examples include seagull effect for the cello (e.g. Vox Balaenae), metallic vibrato for the piano (e.g. Five Pieces for Piano), and using a mallet to play the strings of a contrabass (e.g. Madrigals, Book I), among numerous others. He is not an electronic music composer; however, many works call for amplification of instruments, such as Black Angels (string quartet) or Ancient Voices of Children (mixed ensemble). Crumb's music contains an intense humanism, which is reflected in his personal definition of music: "a system of proportions in the service of spiritual impulse."