WaveWarp 2.0 Component
      
Signal Generators:
Exponential Sweep Control Generator (F)
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Functional Description
Generates a control signal which
(repeatedly) ramps from a selected lower value to
a selected upper value, and back to the lower value,
over a chosen time period,
following an exponential profile on the rise and fall.
The ouput is
scaled to have numerical values which pertain to
audio frequencies in hertz
(designed for use as a "Frequency" controller).
For efficiency, the waveform is pre-calculated and
stored in a wavetable (buffer).
This component is useful for building a phaser effect from scratch,
by using its output to control the center-frequency
of a time-varying notch filter.
NOTE: the sample rate at which this component is executed can be arbitrarily set via the
"Sample-rate setting for Signal Generators and
Input ASCII files" button
(or the "Sample-Rate Setting" command under the "Edit" menu) on the toolbar, which is
activated whenever the component is selected on the DrawingBoard.
Equivalently, it can be set via the dialog box which (i) appears
when the component is initially
dragged on to the DrawingBoard or (ii) is activated using the right-mouse-button when
the component is selected on the DrawingBoard.
This procedure allows the component to either (i) enforce
a user-determined sample rate on the downstream component(s), or (ii) to inherit the sample rate from
the downstream component(s). Different signal generators can run at different
sample rates on a DrawingBoard, as long as the rules of connectivity
for multiple sample rates are adhered to (see the
WaveWarp Users' Guide
for more information.)
The characteristics of the exponential sweep are adjustable via
the Parameter Window, as summarised in the
following table.
| Parameter | Purpose |
|---|
| "Lower" slider | Sets the lower limit for
the sweep (within the numerical range extending from
0 up to the Nyquist frequency (i.e. half the sample rate)). |
| "Upper" slider | Sets the upper limit for
the sweep (within the numerical range extending from
the lower limit up to the Nyquist frequency). |
| "Rate" slider | Sets the rate (in Hz) at
which the sweep cycles through its
profile from the lower limit to the upper limit. The sweep
follows an exponential rise from the lower limit to the upper limit,
followed by an exponential decay from the upper limit to the lower limit. |
| "Skew" slider | Adjusts the time-asymmetry
of the shape of the exponential sweep. A value of 0.5 corresponds to a symmetric profile
(i.e. the rise profile
is a mirror image of the decay profile). |
| Plot window |
Displays a full sweep cycle, showing the value of the output versus time.
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Algorithm
The exponential sweep profile is stored
in a wavetable, and is scanned using a table-lookup oscillator algorithm
(see
[Moore]
section 3.1.7
and
[Roa] p. 90-95
for further information).
Signal Implementations
| Audio signals | Control signals | Description |
|---|
| n/a | single output | Generates a
control signal with an amplitude suitable for use as a "Frequency" controller |
Related components:
Example DrawingBoards illustrating usage:
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