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.
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).
