ARP2600 - Fundamentals of Music Technology - Cyborgstudio.com

SECTION SEVEN: ADSR AND AR GENERATORS - 059EG’S IN PRACTICEThe envelope generators on the ARP 2600 are used exclusively as a sourceof control voltages. They can be used to control the frequency or pulsewidth of an oscillator or the cutoff frequency of the filter. The ADSR EGis normalled to FM inputs on each oscillator, as well as one of the controlinputs on the VCF. When used to FM a VCO, an envelope generator canproduce a wild disturbance in pitch depending upon how deep the modulationis set. More importantly, the EG’s can be used to raise the filter’sFc every time a key is pressed, and thus stop or gate the sound when anote isn’t being played. Essentially, the envelope generators are a usefultool whenever one wants to have a voltage contour created whenever akey is played. Of course, there are other ways to cause the EG’s to fire,but their use is generally tied to a key press.The level or time of each stage of the EG’s is set using sliders which canbe seen in Figure 7-9. One will note that the EG’s only have outputs, butno inputs, which means that they cannot be modulated. It is possible todesign EG’s which allow voltage control of each stage, but such featuresare a rare item in a commercially-produced synthesizer.Observant persons may note that there is a jack and a switch just belowthe AR generator which has gone unexplained. However, this jack is intimatelyconnected to the module which will be discussed in Section 10, soit is best left unexplained until that time.THE EVOLUTION OF THE EGModern developers have changed the EG in many different ways, but themost simple change has been the addition of more stages. Some companiesoffer DADSR generators, which have a programmable delay timebefore they begin the attack stage. This is particularly useful if manyEG’s are available, as they can all fire at slightly different times after aFigure 7-9: The ADSR andAR generatorskey is pressed. Other synthesizer companies such as E-mu Systems have developed a DADHSR EGwhich not only had the delay stage, but an extra ‘hold’ stage as well. Many modern synthesizers haveabandoned the ADSR concept entirely and have begun to just allow users to set four different timeswith four different levels. Some EGs even have up to eight stages! These super flexible EG’s areexplored in depth in the second volume of this series.