Filter Modulation - Access VIRUS CLASSIC User Manual

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 - espe-
cially 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, auto-
matically 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 initial 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 maxi-
mum level of the envelope may lie outside the audible range when the filter has already been par-
VIRUS CLASSIC MANUAL 21
Introduction