Oscillators; Pulse Width Modulation - Access Virus Rack User Manual

OSCILLATORS

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Pulse Width Modulation

Pulse width modulation is a very effec-
tive method for producing beat oscilla-
tions without having to resort to several
detuned oscillators.
Dial OSC BALANCE to the far left so that
only OSC1 is audible, then select the
waveform Pulse for this oscillator (OSC1
Shape to the right). Slowly turn the Pulse
Width (PW) knob back and forth. As you
change its pulse width, you'll hear move-
ment in the sound itself. When its pulse
width remains fixed, the sound will
remain static. This to-and-fro pulse width
modulation can be automated by means
of an LFO. Select PWM for LFO1 Amount
and set a relatively high modulation
amount. You can vary the intensity of
the modulation via LFO Rate.
Now when you play different sounds,
you'll will find that the intensity of the
modulation is considerably greater with
low-frequency sounds than it is with
higher-frequency sounds. This is due to
the fact that the LFO frequency does not
follow the pitch. You can compensate for
this effect by activating and adjusting
the function LFO1 KEYFOLLOW. When
you set LFO1 KEYFOLLOW to a value of
127, the LFO rate will follow whatever
pitch you play precisely (in octaves).
To come up with a fatter sound, you
should also dial in the second oscillator
(set OSC BALANCE to the center posi-
tion) and use DETUNE to do just that to
its pitch (relative to the first oscillator).
Next to LFO1, LFO3 is also able to gener-
ate pulse width modulation. However,
unlike LFO1, LFO3's modulation algo-
rithm was tweaked specifically to deliver
what we consider hip pulse width modu-
lations. Note that LFO3 PWM often deliv-
ers smoother results, particular a softer,
tighter sound for pads. Another advan-
tage of LFO3 is that it frees up LFO1 so
that you can use it for other sonic chores.
By the way, KEYFOLLOW should also be
activated for LFO3.
ACCESS VIRUS RACK 185
Oscillators