The Lfos - Access Virus Rack User Manual

THE LFOS

When you first started this series of
experiments with sounds, we promised
that many of the functions the Virus can
be "programmed" so that they are exe-
cuted automatically. You have already
learned how to control the volume and
cutoff frequencies of both filters as well
as the pitch and intensity of the fre-
quency modulation of Oscillator 2 via
"preprogrammed" envelopes. These
options are great, but you have already
encountered a number of functions
where it would be a helpful if you could
also program them to be executed auto-
matically. And of course envelopes are
great modulation sources, but you have
to play a note every time you want to
initiate an envelope. During your experi-
ments you probably came across a func-
tion or two you would like to be able to
control periodically - independently of
notes. Some features that come to mind
are traditional techniques such as
vibrato (periodic pitch control) and trem-
olo (periodic volume control). Another
option you might like to have at your
disposal is random parameter control.
In the Virus, both of these tasks are exe-
cuted by a so-called LFO (low frequency
oscillator) that oscillates at frequencies
below the audible range. An LFO is simi-
lar to the oscillators you have encoun-
tered thus far, but it oscillates
significantly slower so that its output sig-
nal is too low for human hearing. So
what good are they if you can't hear
them? LFOs are used in much the same
manner as envelopes, with the major dif-
ference that the are repeated indefi-
nitely.
ACCESS VIRUS RACK 41
The LFOs