A form of synthesis which creates desired timbres and waveforms by starting with complex, harmonic-rich waves and using filters to selectively deemphasize or remove unwanted harmonics. Subtractive synthesis was the method by which nearly all of the classic analog synthesizers of the 1960s and '70s produced their sounds. Two factors coincided to make this the case: it was practical to implement with the technology available at that time, and subtractive synthesis happens to be fairly good at approximating the sounds of many traditional instruments, as well as producing timbres that are novel but not so bizarre as to be incomprehensible or offensive to the casual listener. Subtractive synthesis is good at imitating the physical processes involved in bowed-string, air resonance, and some pluc