Access Virus B, Virus A User Manual

©2000 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. Graphic Design and DTP by Babylonwaves Media.

http://www.access-music.de [e-mail]

CONTENT

INTRODUCTION	- 15
The Virus ..................................................	16
The Amplifier Envelope .......................	20
The First Filter .........................................	23
Filter Modulation ...................................	25
The Saturation Stage ............................	27
The Second Filter...................................	28
Filter Routing ..........................................	32
The First Oscillator................................	34
The Second Oscillator ...........................	37
The MIXER Section................................	39
The LFOs ...................................................	41
LFO 2 .........................................................	46
Velocity....................................................	48
Unison Mode..........................................	49
The Chorus/Flanger Effect..................	50
The Delay Effect......................................	51
More to Come .........................................	52

CONCEPT AND OPERATION	- 53
Operating Modes ..................................	54
The Multi-Single Mode.........................	55

HANDLING	- 59
Parameter Selection and
Data Entry...............................................	60
Knob Modes ...........................................	63
Display of values ...................................	64

ALL ABOUT THE MEMORY	- 67
Store .........................................................	68
Compare..................................................	69

MASTER CLOCK & MIDI-CLOCK - 71

Master Clock and Midi-Clock ..............

72

THE MODULATION MATRIX AND
DEFINABLE KNOB	- 75
Creating Modulation Configurations
via Assign ................................................	76
The Definable Knobs.............................	78

THE EFFECTS SECTION

- 81

Edit Buffers ..............................................	57	The Effect Section	82

AUDIO INPUTS	- 83
Audio Inputs...........................................	84
OSC Volume / Input..............................	85
Input Level Indicator ............................	86

INTERNAL AUDIO ROUTING	- 87
Aux Buses................................................	88
The Audio Outputs ...............................	89

ADDITIONAL FUNCTIONS	- 91
Panic Function .......................................	92
Audition function..................................	92
Reset Function .......................................	92

THE PARAMETERS	- 93
Sound Parameters with a Dedicated
Control Element ....................................	94
LFO 1 – Panel ...........................................	95
LFO 1 – EDIT Menu.................................	97
LFO 2 - Panel .........................................	100
LFO 2 Edit-Menu ...................................	101
LFO 3 ........................................................	102
OSCILLATOR 1- Front Panel................	104
Oscillator 2 – front Panel....................	105
OSCILLATOR – EDIT-Menu................	106

Menu parameters for Oscillator-2	...107
Menu-Parameter for Oscillator-3...	109
Menu-Parameters of the
Suboscillator ...........................................	111
Mixer-Parameters within then
Oscillator-edit-Menu ...........................	112
Mixer ........................................................	113
Filters – Panel.........................................	114
Filter-Edit-Menu....................................	118
Amplifier ................................................	122
Main Edit Menu (Common)...............	123
Assign......................................................	129
Velocity...................................................	133

WITHIN THE CTRL-MENU	- 135
COMMON ..............................................	136
ARPEGGIATOR.......................................	137
DEFINABLE 1 / DEFINABLE 2 ..............	140
MULTI MODE parameters..................	142

PARAMETER OF THE FX-MENU- 149

The internal Effects .............................	150
Input........................................................	150
Follower (Envelope-Follower)...........	154
Ringmodulator .....................................	155
Vocoder ..................................................	156
Distortion...............................................	157

	Analog Boost	158
			THE VOCODER OF THE VIRUS		- 201
	Phaser .....................................................	159
	Chorus	161		Vocoder .................................................	202
				The parameters of the vocoder	204
	Delay/Reverb	162
				Notes about the vocoder	210

GLOBAL-, MIDIAND SYSTEM
PARAMETERS	- 173
Global Parameters ...............................	174
System ...................................................	180

RANDOM PATCH GENERATOR - 183

Random Patches...................................

184

CATEGORIES	- 187
Sound Categories	.................................188

THE KEYBOARD VERSIONS OF
THE VIRUS	- 189
The Virus kb and the Virus Indigo... 190
Local off and “Three in One” ............	190
Keyboard & Company.........................	192
The Keyboard-Modes..........................	195

THE VIRUS AND SEQUENCERS - 213

Parameter Control via MIDI ..............	214
Organizational Information..............	214
Handling MIDI Parameter Control ..	216
Notes on Adaptive Parameter
Smoothing .............................................	217
Problems Related to Parameter
Control....................................................	221
DUMP: The Sound in the Song .........	222

TIPS, TRICKS AND OTHER WORDS
OF WISDOM	- 227
MULTI SINGLE Mode ..........................	228
Value Buttons ......................................	229
All abouts Inputs.................................	229
About the Delay/Reverb.....................	231
The Virus as an Effect Device............	232
Envelope Follower ...............................	233
Oscillators .............................................	234
Filters.......................................................	237
SATURATION for Added Dirt ............	239

LFOs ........................................................	240
Volume Control ...................................	242
ASSIGN and the DEFINABLE Knobs. 243
ARPEGGIATOR......................................	244
MIDI ........................................................	245
PRIORITY ................................................	247
Installing an operating system
update....................................................	247
Loading the Operating System from
One Virus to Another .........................	249
Software Updates ...............................	250

APPENDIX	- 251
System Exclusive Data........................	252
Parameters Describtion.....................	258
Multi Dump Table................................	273
Classes ...................................................	276
Mod Matrix Sources ..........................	280
Mod Matrix Destinations...................	281
Definable Knobs Destinations ........	282
MIDI Implementation Chart.............	284
FCC Information (U.S.A).....................	286
FCC Information (CANADA)..............	288
Other Standards (Rest of World).....	289
Declaration of Conformity................	290
Garantie Bestimmung .......................	292
Warranty ...............................................	293

6

ACCESS VIRUS OS4 7

Important Safety Remarks

Please read and heed the following safety guidelines!

A few fundamental rules on handling electrical devices follow.

Please read all notes carefully before you power the device up.

Don’t expose the device to direct sunlight.

Don’t expose the device to strong vibrations and mechanical shocks.

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.

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.

8 CHAPTER 2

Safety Remarks

Always pull the actual plug, never the cord, when you’re unplugging the device.

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.

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 174).

Care

Do not open the device, it is not equipped with any user-service- able parts. Repair and maintenance may only be carried out by qualified specialists.

Use only a dry, soft cloth or brush to clean the device.

ACCESS VIRUS OS4 9

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 engineeringrelated purposes. Any other use is not permitted and automatically invalidates the warranty extended by Access Music Electronics GmbH.

10 CHAPTER 2

Safety Remarks

ACCESS VIRUS OS4 11

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 - for instance the Prophet 5 or Memorymoog to name just two popular examples of the species - 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 512 slots for storing SINGLE sounds. These are organized in four banks. The first two banks (A and B) are located in the RAM, so you can overwrite them with new sounds. The other

two banks are ”hard-wired”, i.e. they’re programmed into the FLASH ROM.

The Virus offers a maximum of 24 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 80 effects, no less!. 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.

12CHAPTER 3 Prologue

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 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 ”hardwired” or fixed modulation configurations, you can assign three modulation sources to up to six 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

ACCESS VIRUS OS4 13

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 responds 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.

14CHAPTER 3 Prologue

Although far from complete, the features listed above give you some indication that you now own an exceptionally versatile, highquality 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 b. Feel free to get in touch with your local authorized dealer for more info.

Many thanks to:

Ben Crosland, Thomas Green, Axel Hartmann, Uwe G. Hönig, Jörg Hüttner, Oliver Käser, Andrea Mason, Thorsten Matuschowski, Paul Nagle, Kai Niggemann, Rob Papen, Wieland Samolak, Howard Scarr, Hans-Jörg Scheffler, Jenny Simon, Matt Skags, Joeri Vankeirsbilck, Jay Vaughan, Jens Wegerhoff and Daniel Wewer.

Introduction

16CHAPTER 4 Introduction

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 subsection 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

ACCESS VIRUS OS4 17

The Virus

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.

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 indi-

18CHAPTER 4 Introduction

cate the the MIDI Channel, the current Program Bank (A to D) as well as the number and name of the current sound program. 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.

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 and D, 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 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 select 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 “A127 - 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

ACCESS VIRUS OS4 19

The Virus

as possible to give you a basis from which you can begin creating or shaping your own sound.

20CHAPTER 4 Introduction

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 five pots labeled ATTACK,

DECAY, SUSTAIN, TIME 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 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.

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.

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.

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

ACCESS VIRUS OS4 21

The Amplifier Envelope

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.

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 to others, i.e. the effectiveness of a control feature is altered, modified or even negated completely by other related functions.

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

22CHAPTER 4 Introduction

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 next phase of the amplifier envelope is determined by the SUS- TAIN-TIME pot: If the pot is set to the center position (12 o’clock) indicated by the mathematical infinity symbol, then the SUSTAIN level remains constant through to the end of the note.

If you turn it counter-clockwise to the left (towards FALL), then the level drops off at an increasing rate towards the minimum level much in the manner you just experienced with the DECAY pot; If you turn the pot clockwise to the right (towards RISE), the level rises at an increasing rate to maximum and remains there until you release the key.

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.

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.

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

ACCESS VIRUS OS4 23

The First Filter

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 socalled cutoff or filter frequency are suppressed, those below it remain unaffected.Now locate the FILT 1 MODE switch, which is also located in the FILTERS section. It enables you to select a filter operating mode from the four available options:

LP the low pass filter we have just discussed.

24CHAPTER 4 Introduction

HP the high pass filter which works in the opposite manner of the low pass filter: It suppresses the lower frequencies in a signal and lets the higher frequencies pass.

BP the band pass filter which suppresses both ends of the tonal spectrum and allows only a narrowly defined bandwidth of the original sound to pass.

BS The band stop filter, band reject filter or notch filter which works in the opposite manner of the bandpass filter. It allows all of the frequencies of a signal except for a narrow frequency band around the cutoff to pass. The term “notch” is fairly descriptive; you might say this filter chops a notch out of the sound spectrum.

Now activate the different operating modes and rotate the CUTOFF pot to get a feel for the way each filtering option works.

Along with the CUTOFF pot, the RESONANCE pot is the most important control feature of a filter. The filter resonance increases the volume of the frequencies located near the cutoff frequencies and suppresses the more remote frequencies. This sound shaping feature has a striking effect - especially when used in conjunction with the low pass filter: it produces a nasal or honking type of tone which increases as you turn the resonance up. Experiment by varying the RESONANCE setting in the different operating modes in conjunction with different CUTOFF settings. You will find the effect that the RESONANCE pot achieves is markedly different for the band stop filter in comparison to the effect it has on the other filter types: as the resonance increases, the bandwidth of the notch decreases; in other words more frequencies on both sides of the filter frequency are allowed to pass.

FILTER MODULATION

Of course we don’t want to require you to execute every sound modification manually by twiddling pots. All kinds of sound modifications in the Virus can be executed automatically much in the way of your previous experiments with the volume controls: 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 (turns it up or down) an imaginary volume pot.

Similar procedures are applicable to the filter frequencies. The FILTERS section features its own envelope, the structure of which is identical to the amplifier envelope, located directly above the amplifier envelope on the control feature panel. Much like the amplifier envelope, the filter envelope automatically “rotates” the CUTOFF pot.

However there is one significant difference between the two envelopes. With the amplifier envelope, you are always dealing with an ini-

ACCESS VIRUS OS4 25

Filter Modulation

tial volume level of 0 because of course you want absolute silence prior to the beginning of a note.

After the RELEASE phase, it is again highly desirable that your box is silent. With the filter envelope, the situation is somewhat different: It always starts at the CUTOFF value that you determined manually. And it is definitely not always desirable that the filter frequency is brought to the maximum level.

Consequently, you need a tool that limits the effective range of the filter. This is why we equipped the Virus with a control labeled ENV AMOUNT (short for Envelope Amount). When the pot is turned counter-clockwise to the far left, the filter has no effect on the cutoff frequency; the further you turn the pot to the right, the greater the effect the filter envelope has on the filter frequency. The maximum level of the envelope may lie outside the audible range when the filter has already been partially opened via the CUTOFF pot or was manipulated via other control options. In extreme cases where the filter is already completely

26CHAPTER 4 Introduction

open, the filter frequency cannot be increased regardless of how high you set the ENV AMOUNT.

Go ahead and spend some experimenting with different ENV AMOUNT, CUTOFF and RESONANCE settings for the diverse filter operating modes. Also try varying the settings for the amplifier envelope. You will find that with just these few parameters you are able to come up with a vast amount of sound settings. If you are among the many musicians who are associative listeners, you might say many of the settings produce sounds reminiscent of stringed-instruments; some sound picked, plucked or snapped, others sound bowed.

For your next experiment set the amplifier envelope so that you hear a constant level when you press and hold a note. Now deactivate the filter envelope by setting the ENV AMOUNT to 0. Set Filter- 1Filter-1 to low pass mode and decrease the filter frequency until you just barely hear a muddy signal when you play notes in the mid-range.

Now play a few higher and lower notes. You will find that the lower notes have a greater overtone content, whereas the higher notes sound muddier and their volume decreases until the notes are completely inaudible. You might already suspect what this is all about: As the notes are transposed ever lower, more portions of the signal fall below the cutoff frequency, whereas with the notes that are transposed ever higher, more portions of the signal rise above the cutoff frequency and subsequently are suppressed until the root note and the last audible portion of the signal is silenced.

To avoid this effect - or if desirable, to amplify it - you have the option of influencing the cutoff frequency via the pitch of the note, i.e. the note number. The degree of influence is determined by the KEY FOLLOW pot.

Please note that KEY FOLLOW is a so-called bipolar parameter: Its control range is not limited to the positive end of the spectrum (0 to a maximum of 127). Bipolar controls effect negative values as well, in this case from the negative

maximum of -64 through 0 an on to the positive maximum of +63. Consequently, if this pot is set to the center position (12 o’clock or 0) the pitch of the notes corresponding to the keys on your keyboard has no effect on the cutoff frequency. If on the other hand you turn the KEY FOLLOW pot clockwise towards the positive control range, you will find that the filter opens up increasingly as the pitch increases with higher notes. At lower notes, the filter closes down again. If you turn the pot counterclockwise towards the negative control range, the KEY FOLLOW effect is reversed. With the Virus, you will encounter this feature - intensity control via a bipolar parameter - again in conjunction with other modulation sources and targets.

Now experiment as much as you like with different KEY FOLLOW settings and tune the settings via the CUTOFF pot. And remember to bring all of the other parameters you have encountered thus far into play.

ACCESS VIRUS OS4 27

The Saturation Stage

THE SATURATION

STAGE

In the signal chain of the Virus, Fil- ter-1 is followed by a saturation stage. It enables you to add overtones to the filtered signal via distortion. Locate and press the button labeled EDIT in the FILTERS section.

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1 SATURATION

Curve Off≤

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The display will read ”SATURATION CURVE OFF”, which means exactly what it says. With the VALUE buttons or the VALUE pot, you can now select from a number of saturation/distortion curves. Next to the distortion curves, the SATURATION stage offers further DSP effects such as the shaper, rectifier and filter. These are explained in detail in the section on the SATURATION stage.

At this point we would like to mention the OSC VOL pot in the MIXER section. The portion of the control range from the far left to the cen-

28CHAPTER 4 Introduction

ter position (12 o’clock) determines the volume of the filter section’s input signal. The portion of the control range located to the right of the center position (12 o’clock) does not achieve any increase in volume; it simply intensifies the degree of saturation or distortion. This effect is only achieved when you have activated a saturation curve. The intensity of the remaining available DSP effects is also controlled via the OSC VOL knob.

Feel free to experiment with the diverse saturation curves and be sure to vary the OSC VOL settings. Note how the different CUTOFF and RESONANCE settings influence the saturation curve.

THE SECOND FILTER

You probably noticed that by a adding a bit of saturation to the signal you can come up with a pretty heavy, aggressive sound - especially with a low filter frequency level and high resonance. You’re probably thinking these types of sounds could do with some more filtering. We had the same idea, which is one of the reasons why we equipped the Virus with another filter per voice.