The First Oscillator - Access Virus Rack XL User Manual

í

THE FIRST OSCILLATOR

To this point, we have turned our attention ex-
clusively to sound-shaping functions and have
always started with the same basic material: a
so-called sawtooth wave. This waveshape is
especially well-suited as a neutral starting point
as it contains all of the so-called natural scale of
overtones, which give the filter plenty of quality
material to work with.
The filters, with the exception of a notch filter or
band stop (BS), trim the far reaches of the tonal
spectrum, so for instance a signal sounds mud-
dier after it has been routed through a low pass
filter. You can well imagine that this type of
sound modification is substantial but insuf-
ficient for shaping more subtle differences in to-
ne. For instance the tone of a trumpet differs
significantly from that of a saxophone even
though no one would seriously claim that either
of the instruments has a muddier tone than the
other.
What you need is a sound-shaping option for
the portion of a signal that a filter allows to
pass. And of course you also need a tool for de-
termining the pitch of a signal. In synthesizers,
both of these tasks are executed by oscillators.
They oscillate at a variable pitch that can be
modulated and they also generate different wa-
veshapes which give the filters a wider variety
of material to work with.
The Virus is equipped with two main oscillators
and a so-called suboscillator. We will first take a
look at Oscillator 1, which is the oscillator you
have already heard in action during your experi-
ments thus far.
Dial in the same basic sound that you started
with at the very beginning (A127 - START -). To
this end, first press the SINGLE button in order
to return to Play mode from the selected para-
meter section. In Play mode, you can switch
sounds via the VALUE buttons.
Now modify the amplifier envelope so you are
working with a less grating sound, but hold
back on any other filter or saturation modificati-
ons so you can hear the purest oscillator signal
possible.
Locate the section labeled "1", it is bordered off
in a separate area at the far left of the section
labeled OSCILLATORS. No check out the two
encoders labeled SHAPE and WAVE SEL/PW.
These enable you determine the waveshape
and consequently the tonal spectrum of Oscilla-
tor 1.
In the sound program, SHAPE is preset to the
center position. The display shows "Saw" for
the sawtooth waveform.
Press and hold a key and slowly turn the enco-
der clockwise. You should be able to hear how
the tone becomes increasingly more hollow-so-
unding. You might say this effect thins the
sound out, but in any case, the entire tonal
spectrum is affected by an equal measure,
which is an audio result filters are unable to
achieve.
The waveshape that is audible when you turn
the SHAPE encoder to the far right is a so-cal-
led pulse wave. It is unique because the durati-
on of the negative pulse is equal to the duration
of the positive pulse: It has a so-called pulse
width of 50%. The tone of a pulse wave is diffe-
rent to that of a sawtooth wave because it does
not contain all overtones in the natural overtone
scale, only the odd-numbered tones, i.e. the
first (the root note that determines the pitch),
third, fifth, and so forth. By turning the SHAPE
PDF VERSION - RESTRICTIONS APPLY
ACCESS VIRUS RACK XL OS5
The First Oscillator
27