monophonic (adj.)

of recordings, broadcasts, etc., "not stereo, having only one output signal," 1958, coined to be an opposite of stereophonic; from mono- "single" + -phonic, from Greek phōnē "sound, voice," from PIE root *bha- (2) "to speak, tell, say." It was used earlier in music, "pertaining to a style of composition in which one voice-part predominates over the others" (opposed to polyphonic), by 1885.