ARP2600 - Fundamentals of Music Technology - Cyborgstudio.com

SECTION THIRTEEN: KEYBOARD CONTROLS - 103The keyboard’s LFO is normalled into the patch of the keyboard’s CV. More accurately, the keyboard’sLFO actually adds vibrato to the keyboard control voltage itself. Thus, the voltage coming into eachVCO via its normal to the keyboard CV actually fluctuates to create vibrato. This is an importantdesign concept. Because the vibrato is actually added to the keyboard CV signal before it reaches thecabinet, it is possible to use a newer keyboard such as the 3620 with an older cabinet. This is consideredto be a highly desirable combination, since one can have the benefits of a duophonic keyboard and abuilt in LFO with delay while still retaining the older Moog filter design in the cabinet.THE LFO’S PARAMETERSThe keyboard’s LFO offers four parameters. First, the rate and depth of the vibratocan be set. This is no different from the FM patch which was created in Section 3.The vibrato rate is adjusted using the LFO SPEED slider, while the vibrato depthis adjusted using the VIBRATO DEPTH slider. (See Figure 13-6) However, adelay can also be set for this vibrato. Delayed vibrato can be defined as the amountof time from the time a key is pressed to the time the vibrato starts in. It is adjustedusing the VIBRATO DELAY slider. (See Figure 13-6) This effect is highly desirablesince it better simulates real-world vibrato. Before this parameter was madeavailable on the keyboard’s LFO, synthesists would often route the output of theVCO being used as an LFO to an audio input on the VCA. The VCA would thenbe modulated by an EG and the output of the VCA would be fed back to the FMinputs on the VCOs. This patch is illustrated in Figure 13-7. In this patch, oneVCO, the VCA, and one EG are sacrificed to create delayed vibrato. A huge sacrifice,to be sure, but the effect was desirable enough to make it worthwhile formany synthesists.13-6: The keyboard’sLFO sectionVCOLF MODEEGSlow attacksimulates delayVCOVCAVCFEGFigure 13-7: Delayed vibrato without using the keyboard’s LFOToamplifierandspeakersNotice that the VCO in LFmode going to the VCA isa control but, since its amplitudeis actually beingchanged by the VCA, it isnot modulating the VCAitself. The EG modulating the VCAwill gradually increase the VCA’sgain, thus increasing the amount ofthe VCO in LF mode reaching theVCO that is being heard through theVCF. Again, the VCA is illustratedin yellow since it is a carrier whilebeing modulated by an EG and amodulator (the VCO’s signal exitingit to modulate the audio VCO).