PROGRAM > MOD-7: Oscillator 5–4: VPM Osc1
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Key Slope [0…75]
This scales the amount of Drive as you move up and down
the keyboard, with a center point of C4. Key Slope can help
to keep the timbre even across the keyboard, and also help to
minimize aliasing. The Slope Shape parameter, below,
affects how this parameter works.
The steps are in increments of 0.2dB per octave, up to a
maximum of 15dB/oct.
Slope Shape [graphics: symmetric,
high range only]
Key Slope always attenuates Drive above C4. This
parameter selects whether or not it also boosts Drive below
C4.
Offset [0…100]
This introduces a DC Offset into the input signal, shifting the
signal in relation to the waveshaper table.
With a full-scale input signal, this will make the signal clip
on one side or the other, and result in an asymmetric
waveform. When used in conjunction with Drive, it can
select the part of the table used to process the signal. Offset
can be modulated at note-on, which works well with AMS
sources such as Velocity and Exponential Velocity.
Offset also has specific uses with particular tables; see the
individual table descriptions for more information.
For more information, see the diagram “Drive and Offset,”
above.
HPF [0…100]
The output of the waveshaper is processed through a simple
highpass filter. This filter is primarily intended to prevent
DC offsets in the waveshaped signal, which can cause
unexpected clipping at the audio outputs, along with other
strange results.
This parameter controls the cutoff of the filter. The default
value of 5 is generally sufficient to block DC offsets. Higher
values will make the sound increasingly thin, which may be
useful for creative purposes.
Makeup Gain [-36dB…0dB…+36dB]
This provides additional gain to compensate for loss through
the Waveshaper. For information on how to use this, see
“Tip: Modulating Drive,” below.
Drive Parameter Details
These items appear in the Parameter Details area when any
of the parameters in the Waveshaper section other than
Offset are selected. This includes Table, Drive, Key Slope,
Slope Shape, HPF, and Makeup Gain.
AMS [List of AMS Sources]
This selects an AMS source to control the Drive. For a list of
AMS sources, see “Alternate Modulation Source (AMS)
List” on page 901.
Intensity [–72dB…+72dB]
This controls the depth and direction of the Drive
modulation.
Tip: Modulating Drive
Modulating Drive can be extremely useful for creating
dynamic timbres. Depending on the selected table, this
modulation will also often cause significant changes in
overall level. You can compensate for this with a
combination of Makeup Gain and Output Level
modulation:
1. Set up an AMS source to modulate Drive.
2. Assign the same AMS source to modulate the main
Output Level, inversely from Drive.
In other words, if you use a positive intensity for Drive
AMS, use a negative intensity for Output Level AMS.
3. Adjust the Output Level AMS Intensity until the
volume level stays sufficiently even.
The actual settings will vary depending on the input level
and the selected table. Don’t expect the Output Level
intensity to be the same as that of Drive.
4. Increase the Waveshaper’s Makeup Gain parameter
to compensate for the reduction in volume.
Offset Parameter Details
These items appear in the Parameter Details area when the
Waveshaper Offset parameter is selected.
AMS [List of AMS Sources]
This selects an AMS source to control the Offset. For a list
of AMS sources, see “Alternate Modulation Source (AMS)
List” on page 901.
Offset can be modulated at note-on only. This works well
with AMS sources such as Velocity and Exponential
Vel oc ity.
Intensity [–100…+100]
This controls the depth and direction of the AMS modulation
for Offset.
5–4d: Keyboard Track
Each VPM Oscillator has its own keyboard tracking, which
is dedicated to modulating the Output Level as you play up
and down the keyboard.
NAUTILUS’s keyboard tracking can be fairly complex, if
desired. You can create different rates of change over up to
four different parts of the keyboard.
Tracking for timbre
Most acoustic instruments change in timbre as you play
higher or lower pitches. At its most basic, keyboard tracking
can compensate for these effects by adjusting the output
level of an FM Modulator as you play higher and lower on
the keyboard. With Modulators, raising the level will make
the timbre brighter; reducing the level will make it darker.
Tracking for aliasing
With FM, aliasing generally increases at higher frequencies
(see “Aliasing” on page 301). Reducing Modulator levels at
higher pitches is usually the most effective way to minimize
aliasing.
How it works: Keys and Ramps
The keyboard tracking works by creating four ramps, or
slopes, between five keys on the keyboard. The bottom and
top keys are fixed at the bottom and top of the MIDI range,
respectively. You can set the other three keys–named Low
Break, Center, and High Break–to be anywhere in
between.
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