This term is normally used to refer to the tradional synthesis model used by analog synthesizers in the 1970s. It is also known as subtractive synthesis. It involves oscillators, the outputs of which are mixed together and fed into a filter (where certain frequencies are subtracted) after which they are fed through an amplifier. The amplifier and filter are normally also driven by envelope generators....
Eight-Voice
Originally owners of the Four-Voice could expand it to up to eight SEM modules. Shown
here is an example of just that. This became the first Eight-Voice.
Later Oberheim released an Eight-Voice with two keyboards, (one on top of the other:
the top one, a 4-octave(C-C), 49-note, and the bottom one, a 5-octave(C-C), 61-note)
and an onboard Digital Programmer which held 16 presets. Currently we have no
picture of this one.