Spectral analyses were applied to the courtship songs of the mutants cacophony (cac), dissonance (diss), fruitless (fru), and period (per), as well as to the double mutant cac diss. Aberrant intervals between song pulses were observed in diss, cac, cac diss, and fru songs. diss males displayed a defect in song hums manifested by an irregular sine wave, although the fundamental frequencies were normal. Sine song frequencies and intrapulse frequencies were aberrant in cac diss males. Two per mutant alleles (pero1 and pers) were associated with normal song [corrected] pulses and hums. These findings are discussed with regard to the mechanisms of song production and the role of these sounds in Drosophila reproduction.