User manual ACCESS VIRUS C

ACCESS VIRUS C SERIES USER MANUAL OS5 ENGLISH VERSION ©2002 Access Music GmbH, Germany. VIRUS is a trademark of Access Music GmbH. All other trademarks contained herein are the property of their respective owners. All features and specifications subject to change without notice. Written by Christoph Kemper, Uwe G. Hönig, Wiland Samolak and Marc Schlaile. Translation by Thomas Green and Howard Scarr. Graphic Design and DTP by Babylonwaves Media. http://www.access-music.de info@access-music.de 2 1 Content IMPORTANT SAFETY REMARKS Handling............................................................... 44 All about the memory ........................................... 47 The Modulation Matrix and Soft Knobs..................48 Random Patch Generator......................................50 Categories............................................................ 52 The Effects Section............................................... 52 Audio Inputs ......................................................... 53 Internal Audio Routing .......................................... 54 Additional functions .............................................. 55 PROLOGUE SYNTHESIS PARAMETERS INTRODUCTION The Virus ............................................................. 14 The Amplifier Envelope ........................................ 17 The First Filter...................................................... 18 Filter Modulation .................................................. 19 The Saturation Stage ........................................... 21 The Second Filter ................................................. 21 Filter Routing ....................................................... 24 The First Oscillator ............................................... 25 The Second Oscillator .......................................... 27 The Third Oscillator.............................................. 29 The Mixer Section ................................................ 29 The LFOs ............................................................. 30 The MOD Section ................................................. 33 Soft Knob 1/2....................................................... 33 Volume and Panorama Position ............................ 34 Velocity................................................................ 34 Unison Mode........................................................ 35 The Effects........................................................... 36 The Arpeggiator ................................................... 38 SoundDiver Virus ................................................. 38 More to Come ...................................................... 39 OSCILLATORS ...................................................... 58 Oscillator-1/2/3 (Panel).........................................58 Oscillator (Edit-Menu) ........................................... 59 FILTER ................................................................. 63 Filters (Panel) ....................................................... 63 Filter Envelope...................................................... 64 Filter-Edit-Menu ................................................... 65 ENVELOPES ......................................................... 69 MIXER .................................................................. 70 LFO AND MODMATRIX .........................................71 LFO (Panel)........................................................... 71 LFO (Edit Menu).................................................... 73 ARPEGGIATOR EDIT.............................................. 80 THE INTERNAL EFFECTS ......................................82 Distortion (Panel) .................................................. 82 Chorus (Panel) ...................................................... 83 Chorus (Edit Menu) ............................................... 83 Phaser (Panel) ...................................................... 84 Phaser (Edit Menu) ............................................... 84 Delay / Reverb...................................................... 85 Delay / Reverb (Panel) .......................................... 86 Delay / Reverb (Menu) .......................................... 87 Vocoder................................................................ 92 Analog Boost ........................................................ 92 Equalizer .............................................................. 92 CONCEPT AND OPERATION Operating Modes ................................................. 42 Master Clock and Midi-Clock ............................... 44 ACCESS VIRUS OS5 3 MAIN EDIT MENU Common .............................................................. 96 Unison Mode........................................................ 99 Punch Intensity .................................................. 100 Envelope Sustain Time....................................... 100 Analog Inputs..................................................... 100 Follower (Envelope-Follower) ............................. 102 Ringmodulator ................................................... 102 Second Output/Surround.................................... 103 Velocity.............................................................. 104 Sound Category ................................................. 106 Soft Knob-1/2 .................................................... 106 Problems Related to Parameter Control ..............144 Arrangement Dump - The Sound in the Song......145 TIPS AND TRICKS All abouts Inputs................................................. 148 About the Delay/Reverb ......................................149 The Virus as an Effect Device .............................150 Envelope Follower .............................................. 150 Oscillators .......................................................... 151 Filters................................................................. 153 Saturation for Added Grit and Dirt .......................153 LFOs .................................................................. 154 Volume Control................................................... 155 Assign and the Soft Knobs ..................................156 Arpeggiator ........................................................ 156 How to modulate the Vocoder parameters ..........156 MIDI ................................................................... 157 How to install Updates ........................................158 MULTI MODE & SYSTEM SETUP MULTI MODE PARAMETERS .............................. 110 SYSTEM ............................................................ 114 Keyboard ........................................................... 114 Input .................................................................. 116 MIDI................................................................... 117 System .............................................................. 121 APPENDIX System Exclusive Data .......................................162 Parameter Descriptions ......................................166 Multi Dump Table ............................................... 178 Classes .............................................................. 180 Mod Matrix Sources .......................................... 182 Mod Matrix Destinations .....................................183 Soft Knob Destinations ......................................184 MIDI Implementation Chart .................................185 FCC Information (U.S.A) ......................................186 FCC Information (CANADA) .................................187 Other Standards (Rest of World)..........................187 Declaration of Conformity ...................................188 Garantie Bestimmung .........................................189 Warranty ............................................................ 190 THE KEYBOARD VERSIONS OF THE VIRUS The VIRUS kc and the indigo ............................. 126 The Keyboard-Modes ......................................... 128 THE VOCODER OF THE VIRUS Vocoder ............................................................. 132 The parameters of the VIRUS Vocoder ................ 134 Notes about the vocoder: ................................... 137 THE VIRUS AND SEQUENCERS 4 1 INDEX INDEX ................................................................ 192 Important Safety Remarks 6 2 Important Safety Remarks Please read all notes carefully before you power the device up. A few fundamental rules on handling electrical devices follow. OPERATION · Don't set beverages or any other receptacle containing liquids on the device. · Make sure the device is placed on a solid base. Set it on a stable tabletop or mount it to a rack. · Make sure that no foreign objects fall into or somehow end up inside the device's housing. In the event that this should occur, switch the device off and pull the power plug. Then get in touch with an authorized dealer. · Used on its own and in conjunction with amps, loudspeakers or headphones, this device is able to generate levels that can lead to irreversible hearing damage. For this reason, always operate it at a reasonable volume level. SET-UP · Operate and store the device in enclosed rooms only. · Never expose the device to a damp environment. · Never operate or store the device in extremely dusty or dirty environments. · Assure that air can circulate freely on all sides of the device, especially when you mount it to a rack. · Don't set the device in the immediate vicinity of heat sources such as radiators. · Don't expose the device to direct sunlight. · Don't expose the device to strong vibrations and mechanical shocks. MEMORY BATTERY CHANGE The VIRUS stores its sound programs in a battery-buffered RAM. This battery (general type designation: CR2032) should be replaced every three to four years. The housing has to be opened to change the battery, so take the device to a qualified service technician. Do your part in protecting our environment and take it to a shop that disposes of batteries properly. Before you have the battery changed, save the entire memory content of the RAM by loading it to a sequencer via "Total Dump". Be advised that RAM content is lost when the battery is swapped (see "Midi Dump TX" on page 117).). CONNECTIONS · Be sure to use exclusively the included mains power supply adapter. · Plug the device only into mains sockets that are properly grounded in compliance with statutory regulations. · Never modify the included power cord. If its plug does not fit the sockets you have available, take it to a qualified electrician. · Always pull the power plug out of the mains socket when you won't be using the device for prolonged periods. · Never touch the mains plug with wet hands. · Always pull the actual plug, never the cord, when you're unplugging the device. CARE · Do not open the device, it is not equipped with any user-serviceable parts. Repair and maintenance may only be carried out by qualified specialists. ACCESS VIRUS OS5 7 · Use only a dry, soft cloth or brush to clean the device. · Do not use alcohol, solvents or similar chemicals. These can damage the surface of the housing. FITNESS FOR PURPOSE This device is designed exclusively to generate low-frequency audio signals for sound engineering-related purposes. Any other use is not permitted and automatically invalidates the warranty extended by Access Music Electronics GmbH. 8 2 Important Safety Remarks Prologue 10 CHAPTER 3 Prologue Dear VIRUS Owner, Congratulations on your choice, the new VIRUS. You have purchased a cutting-edge synthesizer that comes fully loaded with several revolutionary features. Here are just a few of the highlights: The VIRUS delivers the sound characteristics and tone of traditional analog synthesizers in a previously unparalleled level of quality and handling ease. We're not kidding, the VIRUS actual delivers the authentic response of an analog synth via a digital signal processor chip, although the sound shaping and voicing options out-perform those of it historical predecessors by a considerable margin. The VIRUS comes with up to 1024 slots for storing SINGLE sounds. These are organized in eight banks. The first two banks (A and B) are located in the RAM, so you can overwrite them with new sounds. The other six banks are "hard-wired", i.e. they're programmed into the FLASH ROM. To make use of the banks E-H you need to install the second1024.mid file first ("The 1024 sounds update" on page 158). The VIRUS offers a maximum of 32 voices. In Multi Mode, these are allocated dynamically to sixteen simultaneously available sounds. You have no less than three audio oscillators plus one suboscillator, a noise generator, a ring modulator, two Multi Mode filters, two envelopes, a stereo VCA, three LFOs and a saturation stage (SATURATOR) for cascade filtering, tube and distortion effects. The VIRUS offers a veritable arsenal of effects. You have seven powerful sound-sculpting functions, including chorus, phaser and distortion, at your disposal, with each effect available separately for every sound. Thus, in 16-way MULTI mode, the VIRUS offers over 98 effects, no less!. Among them you also get a global reverb/ delay unit that lets you create high-quality reverb effects and rhythmic delay taps. Delay time can be synced up to MIDI clock. With the benefit of two external audio inputs, the VIRUS may also serve as an FX device and signal processor that you can use creatively to come up with all kinds of effects. External signals can be processed with filter, gate and lo-fi effects, routed to the VIRUS effects section and serve as a modulation source for frequency and ring modulation. Beyond that, you can use internal or external signals as sources for the VIRUS' on-board vocoder serve. The vocoder works with up to 32 filter bands and offers diverse manipulation and modulation options. The three main oscillators produce 66 waveshapes, three of which are dynamically mixable so that spectral effects are possible within the confines of a single oscillator. In conventional synthesizers, this type of effect requires several oscillators. Synchronization, frequency modulation and ring modulation between the audio oscillators delivers additional complex spectral effects that you can use for all kinds of sound shaping purposes. The filters can be switched in series or in parallel within the voices via several options. When you switch the filters in series, the saturation stage is embedded between the filters. Consequently, an overdriven filter resonance can be re-filtered within the same voice! A maximum of six filter poles (36 dB slope!) enables radical tonal manipulations. The LFOs feature 68 continuous variable waveshapes each, including a triangle with variable symmetry and infinitely variable aperiodic oscillations for random variation of the controlled parameters. The LFOs are capable of polyphonic as well as monophonic oscillation. In other words, if several voices are active, the ACCESS VIRUS OS5 11 LFOs can run independently or in sync. A number of keyboard trigger options enable you start LFO waveshapes with variable phase lengths at the beginning of a note and/or to cycle once only, like an envelope. Next to the numerous "hard-wired" or fixed modulation configurations, you can assign three modulation sources to up to nine different modulation destinations via the Modulation Matrix. For your modulation sources, you have LFOs, velocity, the pitch bender, aftertouch, the modulation wheel, numerous MIDI controllers and other sources to chose from. For your modulation destinations, you can select any sound parameter of the VIRUS that is conducive to being remote controlled. Up to 16 arpeggiators are available in MULTI mode. These give you countless options for creating arpeggios, which can also be synced up to MIDI clock. Sounds and effects are patched out via six audio outputs which of course can also be used to route three stereo signals out. In additional to its killer sounds and tone, the VIRUS was designed to deliver ultimate handling and control comfort. It is equipped with dedicated knobs and buttons for the crucial synthesizer functions, further parameters are accessible via data entry procedures. We distinguished between these two levels of expertise to enable you to create complex sounds while keeping the user interface as clear and uncluttered as possible. In all modesty, we are especially proud of a feature we developed called Adaptive Parameter Smoothing. For the first time in the history of synthesizers equipped with memories, you can manipulate a knob or control feature without an audible step or increment. In other words, the sound does not change abruptly but SEAMLESSLY. No more zipper noises! The VIRUS re- sponds just as smoothly as analog synthesizers did prior to the introduction of digital sound storage And users of contemporary software sequencers will appreciate the fact that the VIRUS sends all sound shaping commands immediately in the form of MIDI Controller or Poly Pressure data (and of course accepts all of the corresponding Controller and SysEx messages). This feature lets you dynamically control the VIRUS and all its functions via computer. Although far from complete, the features listed above give you some indication that you now own an exceptionally versatile, high-quality musical instrument that will give you plenty of joy for years to come. We certainly hope you can fully exploit the enormous potential of this fine instrument. Have fun and enjoy! Your VIRUS Development Team By the way: a rack mounting kit is optionally available for the Virus C. Feel free to get in touch with your local authorized dealer for more info. Many thanks to: Ben Crosland, Maik Fliege, Thomas Green, Axel Hartmann, Uwe G. Hönig, Jörg Hüttner, Timo Kaluza, Oliver Käser, Andrea Mason, Thorsten Matuschowski, Jörg Meißner, Paul Nagel, Kai Niggemann, Rob Papen, Matt Picone, Wieland Samolak, Daniela Sauerbier, Howard Scarr, Hans-Jörg Scheffler, Shehryar Lasi, Jenny Simon, Matt Skags, Joeri Vankeirsbilck, Jay Vaughan, Jens Wegerhoff and Daniel Wewer. 12 CHAPTER 3 Prologue Introduction 14 CHAPTER 4 Introduction í THE VIRUS This section provides deliberate, step-by-step guidelines on operating and handling the VIRUS for those of you who are new to the world of synthesizers and MIDI. The following covers basics such as how to connect the VIRUS to an AC power supply, your MIDI system and your audio system. Then we will guide you through a series of experiments designed to demonstrate the different functional groups, their control features and the tasks they execute. After you have finished reading this section, you will be able to handle virtually all of the sound generating and sound shaping functions of the VIRUS. All of these are described in context, along with their control features. Even the majority of less significant functions, accessible via menus, are discussed here. You will find a detailed, comprehensive description of all functions of your new synthesizer in the section following this introduction. Please keep in mind that within confines of this introduction, we are unable to impart all of the knowledge and skills in acoustics, sound synthesis and MIDI control you might desire or need to acquire. If you are keen to learn more about these subjects, you should consider becoming a regular reader of one or several of the leading trade publications in your country. Your local musical instruments dealer or more experienced musicians will be able to recommend the best magazines to you. And of course there is a wide range of books available on these subjects. If you decide to read this section, we recommend you read it in its entirety from the start rather than begin with a subsection that is of particular interest to you. A fitting metaphor for the basics discussed in this section might be a house where each bit of information in a sub- section is a brick that builds on a preceding brick and interlocks with those next to it. You want your knowledge base to be a sound structure so you won't run into problems when you find one of the "bricks" is missing. CABLE CONNECTIONS Before you connect the VIRUS to an AC outlet and the rest of your equipment, ensure that all of the devices are switched OFF. If your VIRUS does not have a build-in keyboard, then connect the MIDI OUT of the desired MIDI send device (keyboard, computer, hardware sequencer, etc.) with the MIDI IN of the VIRUS. Connect the audio outputs of the VIRUS with the signal inputs of your audio system. In order to receive a signal, as a minimum you must connect the output OUT 1 R/MONO. However, we recommend you also connect the output OUT 1 L so you are able to enjoy the stereo sounds of the VIRUS. Once you have established the desired cable connections, make sure the main volume controls of all the connected devices (VIRUS: MASTER VOLUME, located at the upper left hand of the control panel) are dialed to the lowest possible setting. Switch the devices on in the following sequence: the MIDI send device (computer, master keyboard, etc.) first, then the sound generators (VIRUS and the other signal sources), followed by the mixing console and finally the amplifier. Now while you are sending notes on MIDI Channel 1 of the VIRUS, turn the master volumes of the connected devices up in the same order that you switched the devices on. Be sure to keep on eye on the signal level indicators of your mixing console. ACCESS VIRUS OS5 The Virus 15 MASTER VOLUME Controls the overall volume of the VIRUS. This control determines the volume of the signal pair piped through Output 1 before it is converted into an analog signal. This means that under normal circumstances, you should turn Master Volume all they way up because you of course want the VIRUS to deliver the most dynamic signal possible. and so on, simply use the PARAMETER/BANK buttons to step from one program bank to another. You'll find that some sound programs are labeled with the abbreviations "INP" or "VOC". These use the external audio input as a signal source for the filter section (INP) or vocoder (VOC). This means that you won't hear anything until you route an audio signal into the external audio inputs. LISTENING TO THE FACTORY SOUNDS The program memory of the VIRUS was loaded with sound programs (SINGLE PROGRAMs) and sound combinations (MULTI PROGRAMs) before it left the factory. To hear the SINGLE PROGRAMs (and gain an initial impression of the possibilities your new instrument has to offer in terms of sounds), first make sure your MIDI source is sending on MIDI Channel 1. Press the SINGLE button. A number, a letter, number and name appear in the display. These indicate the the MIDI Channel, the current Program Bank (A to D or A to H) as well as the number and name of the current sound program. MULTISINGLE UNDO STORE MULTI SINGLE + SOFT KNOB 1 í Tip: You can trigger a note on the Virus by pressing both the EDIT and SYNC buttons in the OSCILLATORS section at the same time ­ this is the AUDITION function, which is especially useful for auditioning sounds when there is no keyboard connected to the Virus. í Now if you play notes you should be able to hear this sound and a note (the round dot at the end of the note staff is solid black) should appear in the display every time you press a key and release a key. If you do not hear a sound but you see a half note (blank note head) check to see if you are sending on the wrong MIDI Channel. Call up each of the 128 programs in Bank A in turn. You can do this either with the VALUE keys (which simply increment/decrement the program number), or by holding down the MULTI key and scrolling through programs with the VALUE knob. To try out all the other sounds in banks B to H, simply switch banks with the PARAMETER/BANK buttons. Press the VALUE button to call up the 128 single programs of Bank A in sequence. (The VALUE pot is inactive in this operating mode.) In order to hear the sound programs in banks B, C 16 CHAPTER 4 Introduction SOUND CATEGORIES To help you find the type of SINGLE sound you are looking for more quickly, the Virus operating system lets you define so-called ,,categories" and save this information together with each of your SINGLE sounds. Available categories are: Off, Lead, Bass, Pad, Decay, Pluck, Acid, Classic, Arpeggiator, Effects, Drums, Percussion, Inp u t , Vo c o d e r, F a v o u r i t e 1 , F a v o u r i t e 2 , Favourite3 Each SINGLE sound can ,,belong" to two categories at the same time. Of course the categories of all the presets in Banks C to H are fixed, but for sounds in the RAM Banks (A and B) they can be defined and saved together with the program. To search for sounds in a specific category (in SINGLE or MULTI-SINGLE mode): Press and hold the SINGLE button. This causes the currently selected category to appear in the display, and it can be changed by stepping up or down with the Parameter buttons. Having found the category you want, do not release the SINGLE button and scroll through the sounds using the Value buttons. Release the SINGLE button when you have found what you are looking for. SINGLE sounds which do not belong to the currently selected category are simply skipped over. lect these combination programs via the VALUE button. The VIRUS features "only" 128 MULTI PROGRAMs, so you don't have to switch back and forth between banks they way you just did while activating single programs. The majority of available MULTI PROGRAMs contain sound combinations that are controlled via a single MIDI channel. In these MULTI PROGRAMs, the sounds involved are allocated side-by-side (split) or on top of one another (layered) on the keyboard. In other MULTI PROGRAMs, the sounds are divided up over several MIDI channels to make it easier to work with a sequencer. If you activate a MULTI PROGRAM and hear a single sound only, then you can control this MULTI PROGRAM via several channels. YOUR FIRST SOUND PROGRAM If you have never created or changed a sound on a synthesizer, we now have the pleasure of introducing you to this fascinating process. Select the single program "C127 - START -". Press any key on the connected keyboard. You should hear a sound that, for lack of better description, is a bit harsh or biting, but above all completely static. It should start immediately after you press a key and sustain indefinitely for as long as you hold the key down. As soon as you release the key, the sound should end abruptly. This sound is not designed to be especially pleasant; it is intended to be as neutral as possible to give you a basis from which you can begin creating or shaping your own sound. LISTENING TO THE MULTI PROGRAMS The VIRUS not only has the capability of playing SINGLE PROGAMs, but also combinations consisting of more than one sound simultaneously (MIDI Multi Mode). To call up the MULTI PROGRAMs, press the MULTI button and se- ACCESS VIRUS OS5 The Amplifier Envelope 17 í THE AMPLIFIER ENVELOPE Long-term exposure to this sound will definitely grate on your nerves, so let's get started with changing it into a signal you might enjoy hearing, beginning with the volume characteristics. Locate the section labeled AMPLIFIER at the bottom right of the control feature panel of the VIRUS. Here you can see four pots labeled ATTACK, DECAY, SUSTAIN and RELEASE, respectively. These controls will help you to dial in volume characteristics called an amplifier envelope and put an end to the nerve-racking drone that may remind you of one of those cheesy organs that you hear in `60s B-movie sound tracks. Rotate the ATTACK pot while you repeatedly AMPLIFIER 6 6 6 6 Take a look at the display of the VIRUS to gain an impression of the difference between these two values. It shows two numeric values when you dial a pot: at the left you can see the value stored in the sound program and at the right, the numeric equivalent to the value determined by the current position of the pot. í Always keep in mind that for a programmable synthesizer the position of the control feature or pot does not necessarily indicate the actual value of the given function. The reason for this is that when you first activate a sound program, it will reflect the programmed value. You have to adjust the control feature before the programmed value is superseded by the value you determine manually. 0 12 0 12 0 12 0 12 ATTACK DECAY SUSTAIN RELEASE Now fiddle with the DECAY pot while you repeatedly press a key to activate a note. Hold the key down for good while. You will notice that the volume, once it reaches maximum level at the end of the ATTACK phase, drops until it reaches a minimum level. The DECAY pot determines the speed, or in synthesizer jargon, the rate at which the volume decreases. However, the DECAY level does not always drop to the minimum level; you can determine a random value between the maximum and minimum levels at which the volume remains constant. This level in turn is controlled via the SUSTAIN pot. Whenever the SUSTAIN level is set to maximum, the volume cannot drop during the DECAY phase; in other words, in this situation the DECAY pot is ineffective. engage a key to hear the note. The further you turn the pot up, the longer it takes for the sound to achieve maximum volume after the start of the note. So you can say ATTACK controls the initial volume swell of the sound. Presumably the ATTACK pot was set to a random position before you made any adjustments. Nevertheless the volume automatically increased to the maximum level before you started rotating the pot. The reason for this is that an ATTACK value of 0 is saved in the sound program - START - and this value remains valid until you determine a new value by adjusting the position of the pot, even if you turn it ever so slightly. í The individual functions of a synthesizer are designed to interact; many functions are dependent on other functions. In a number of cases this means that some functions are subordinate 18 CHAPTER 4 Introduction to others, i.e. the effectiveness of a control feature is altered, modified or even negated completely by other related functions. í THE FIRST FILTER Now we will take a look at a component of a synthesizer that is generally regarded as the most important functional unit as it enables drastic sound shaping measures: the filter - or in the case of the VIRUS, the two filters. But first we will concentrate on just one of the two filters. The final pot, RELEASE, determines the speed or rate at which the volume decreases when you release the key: At low values the sound ends relatively abruptly, at high values, the sound fades out more gradually and softly. The length of the RELEASE phase also depends on which level the amplifier curve is at when you release the key: The lower the level, the shorter the RELEASE phase. If you dialed in a brief DECAY or SUSTAIN-TIME phase and it ended while you held the key down then of course there will not be an audible RELEASE phase. The amplifier envelope can be described as a variable curve which, depending on the type and duration of attack, hold and release data, automatically influences an imaginary volume pot (turns it up or down). At the beginning of the note, ATTACK controls the rise or rate of increase to the maximum level. Once the maximum level is achieved, DECAY determines the fall or rate of decrease to the SUSTAIN value, which is infinitely variable between the minimum and maximum levels. The amplifier envelope may remain at this value until the end of the note, fall towards the minimum level as determined by the variable TIME value, or even rise again towards the maximum level. After the end of the note, RELEASE controls the fall or rate of decrease to the minimum level. Consequently, the control pots labeled ATTACK, DECAY, TIME and RELEASE control a speed or rate, where as SUSTAIN actually controls a level. FILTERS 6 6 0 1+2 0 12 0 12 -100% 100% 1 2 CUTOFF 0 RESONANCE ENV AMOUNT FILTER BALANCE FILT 1 FILT 2 LP HP BP -6 6 BS EDIT FILT 1 MODE FILT 2 SELECT CUTOFF 2 Locate the Cutoff pot (not to be confused with Cutoff 2!) in the section labeled FILTERS, directly above the section labeled AMPLIFIER. Rotate the pot to the left and right and note how the sound becomes muddier and clearer in response to the direction in which you turn the pot. (To ensure this effect and the following aural experiments are most pronounced, adjust the amplifier envelope so that the VIRUS generates a constant level while you hold a key down). This is how a low pass filter works: it suppresses, or in technical jargon, attenuates the higher frequencies in a signal and allows the lower frequencies through. Think of the Cutoff pot as a bouncer and the VIRUS as your pub. You can tell it which frequencies to let in and which frequencies to keep out. The frequencies above the so-called cutoff or filter frequency are suppressed, those below it remain unaffected.