ARP2600 - Fundamentals of Music Technology - Cyborgstudio.com

SECTION9 MIXER SECTIONTHE MIXERThe mixer section is a module of the synthesizer that has been used almostsince the beginning of this book, but has yet to be explained fully. The mixersection is one of the most simple modules, and easiest modules to understand.The mixer performs a simple task: it combines two different signalsand prepares them for output to the ARP 2600’s internal amplifier. One cansee in Figure 9-1 that the mixer features two audio inputs. Each one featuresan attenuation slider so that the signals can be combined at the desired levels.Note that the outputs of the VCF and VCA are normalled to the mixer’sinputs. This makes sense, since these are the two modules most likely to beat the end of the signal chain of a patch (not counting the mixer section,which has to be at the end of every patch if one wants to hear any sound atall).The mixer’s signal flow is easy to see by following the white lines screenedon the ARP’s front panel. One can see in Figure 9-1 that first, each inputleads to a separate jack. Unfortunately, there is no mention of the function ofthese jacks anywhere in the ARP 2600’s user manual. (A copy of the author’suser manual is available on-line at http://www.EmusicDIY.com/arp/pages.)These jacks aren’t labeled, which makes it rather difficult to discover theirpurpose. Careful inspection of the 2600’s schematics reveal that these jacksare individual outputs. These jacks pass a copy of whatever comes in eachinput back out. However, when a plug is inserted into them, they cut off thesignal flowing to the mixer and then to the amplifier and speakers. One mightthink that this would render them completely useless, but this is not reallyso. They allow either of the sliders on the mixer to be used to attenuate audioor control signals independently of any other module.Figure 9-1: The mixer sectionIt is interesting to note that while the mixer has been used exclusively for audio signals to this point, itis possible to use it to mix control signals as well. This technique is of rather dubious value, however,since the mixer’s ability to mix and attenuate incoming audio signals is lost when it is used with controlvoltages. There are modules better suited to this task which will be explored in the next section.PANNINGIn the next part of the mixer, the white lines converge and meet at one output. This is where the actualmixing occurs. Whatever is input to the mixer’s two channels appears here at this single output. However,this jack is more than an output. It is also an input. Incoming signals are fed to the next part of themixer: the PAN control. Pan is an abbreviation of the term panoramic potentiometer. The PAN controlsimply determines the amount of signal which is going to each output, and to each speaker. When the070