ARP2600 - Fundamentals of Music Technology - Cyborgstudio.com

SECTION12VOLTAGE PROCESSORSINTRODUCTIONThe voltage processors are an important part of theARP 2600, but are often neglected and misunderstood.While their operation is not difficult to understand,their applications are rather specialized.As such, they are not used as frequently as a VCOor the VCF. The voltage processor module containsthree separate processors. One of the processors isa lag processor and the other two are mixing andinverting processors. The voltage processors are locatedbetween the noise generator and the S/H module.(See Figure 12-1) Two of the three voltage processorslack formal names, so the top one will becalled ‘the first voltage processor’ and the one belowit will be called ‘the second voltage processor.’Figure 12-1: The voltage processorsTHE FIRST VOLTAGE PROCESSORThe first voltage processor mixes and inverts. Five jacks and two sliders comprise this processor. Theinputs are labeled one through four. All of these inputs are summed or mixed together, and come out ofthe remaining jack which isn’t labeled. In this way, this processor acts like a mixer. Inputs two and fourare located on the left hand side of the module, to the left ofthe sliders. (See Figure 12-1) The incoming signals on eachof these jacks can be attenuated using the sliders which areto the right of them. Inputs one and three have no sliders, sotheir levels cannot be attenuated, and nothing is normalledto them. The other normals will be discussed in a moment.Figure 12-2: An uninverted saw waveIt is important to note that both control signals and audio signals work equally well. This processor caneven be used to mix raw direct current or DC. Since this voltage processor can be used as a mixer, itwill almost always be chosen over the mixer module (Section 9) for the purpose of mixing controlsignals. It is a better choice because this voltage processor does not feed the synthesizer’s main outputs.INVERTED FUNBefore the signals reach the output of this processor, they pass through an inverter. This circuit isrepresented on the cabinet’s panel with a triangle and the word INVERTER. An inverter is an electroniccircuit which essentially flips a waveform or incoming voltage upside down. For instance, if oneinputs a saw wave such as the one shown in Figure 12-2, it will be turned upside down at 0 volts asshown in Figure 12-3 on page 92. Another way to describe this is to say that the signal has been moved180 degrees out of phase with the original signal.091