The First Filter - Access VIRUS CLASSIC User Manual

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 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 fre-
quencies 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.
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:
Mode
LOW PASS (LP)
HIGH PASS (HP)
BAND PASS (BP)
BAND STOP (BS)
Now activate the different operating modes and rotate the CUTOFF pot to get a feel for the way
each filtering option works.
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Description
the low pass filter we have just discussed.
the high pass filter which works in the opposite manner of the low pass fil-
ter: It suppresses the lower frequencies in a signal and lets the higher fre-
quencies pass.
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.
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.