ARP2600 - Fundamentals of Music Technology - Cyborgstudio.com

050 - SECTION SIX: VCFTHE ROLE OF THE FILTER IN THE SYNTHESIZERIt is important to realize that filters are not a ‘set and forget’ module of a synthesizer. Although there aretimes when their Fc is set and left at a particular frequency, most of the time, the Fc will be constantlychanged via modulation. This constant change is what brings the sound to life and makes the soundinteresting. There is nothing more deadly than a synthesizer sound that does not change. Some musiciansthink that they can make up for incredibly dull sounds by playing lots of interesting notes, butwhen it comes to synthesizers, the notes that are being played are only half of the music being produced.In the world of synthesizers, the sound itself is as important as the music being played.USING THE VCF AS A MIXERIn addition to control sliders for cutoff frequency, fine tuning of Fc, and resonance amount, a physicalsurvey of the VCF will reveal that it is blessed with eight inputs. The three inputs on the right side arecontrol inputs and the left five inputs are audio inputs. These inputs allow signals to be input to thefilter so that they can be filtered and passed out the filter’s output (right hand side of the filter). It isinteresting to note that signals move left to right even within different synthesizer modules.There are many inputs on the filter so that many different signals can be fed to the filter for filtering atonce. However, the synthesist can use this feature to his/her advantage by using the filter to mix severalsounds together. All of the audio inputs have a slider above them which allows the user to control thevolume level of each signal being input. The inputs are mixed together, filtered, and appear at thefilter’s output.Notice also that each of the filter’s audio inputs is normalled to the output of a different module. One isnormalled to each of the VCO’s, one to the noise generator’s output, and the final one to a module yetto be discovered. Thus, another piece of the puzzle has been filled in for us. The most basic patch startswith oscillators and possibly the noise generator, all of which is then fed to the filter.THE VCF IN PRACTICEUp to this point, this section has dealt with raw factual information about filters, their types, how theywork, etc. However, nothing has been said about how they are commonly used in synthesis applications.Generally, the outputs of the oscillators (and sometimes the noise generator) will be routed to theaudio inputs on the filter (note that they are already normalled there). Notice that there is an attenuationslider above each of the audio inputs. This allows a user to control the volume of each incoming signal.Thus, the filter is a very useful tool for mixing sounds together. When a little resonance is added, andthe filter’s Fc is swept up and/or down, an effect called a filter sweep is created, which is one of themost commonly used filtered sounds today.Another way in which the filter is extremely helpful is that it can stop the constant monotonous outputof the oscillators. Of course, the oscillators continue to oscillate no matter what they are connected to.However, when the filter’s Fc is set low enough, it can stop all sound coming through the filter. Whenthe device in the next section is explored (the envelope generator), the process of automating the changein Fc will be explained.