THE SCIENCE AND APPLICATIONS OF ACOUSTICS - H. H. Arnold ...

560 18. Music and Musical InstrumentsFigure 18.39. Arrangement of modules for an analog synthesizer. The signals from thetwo keyboard-manipulated voltage-controlled amplifier (VCO) are summed into a voltagecontrolledamplifier (VCA) and then relayed to a voltage-controlled filter (VCF). Both VCAand VCF are controlled by the envelope generators (EG). A third oscillator operating atlow frequency (LFO) is on hand for modulation of any voltage-controlled module.In the early years of the synthesizer, control was a cumbersome matter, involvingpatch cords for connecting analog synthesizers. The early digital synthesizers wereeven more cumbersome, none of them operating in real time. In the early 1970s,prepatched analog synthesizers were introduced, primarily for creating specialeffects in a live performance. The setup of the modules is given in Figure 18.39.In the mid 1970s, the modules of Figure 18.39 were combined into a singleintegratedchip. One such chip was placed under each key of the keyboard, so eachkey essentially constituted the control for a miniature synthesizer. The PolyMoogwas the first and the last instrument to be constructed this way. Subsequent designsnow employ digital scanning keyboards and assign a specific sound synthesis chainto each key. The number of chains (generally 8, 12, or 16) establishes the maximumnumber of simultaneous notes.The sequencer was introduced to provide additional automated control. Theearlier sequencers generated several channels of control voltages in repetitivesequences. The analog sequencer could even replace a keyboard for generatinga repetitive bass line. The sequencers have evolved into small computers whichhave almost unlimited musical capabilities. Thanks to computer memory, they