A powerful aspect of Spectron is its ability to provide
"sweeping" or modulation spectral effects.
The sweeps can be controlled by an LFO, or low frequency oscillator, so that the
sweep is based on a timed period. They can also be controlled by the envelope or
level of the incoming audio, so that the sweep is triggered by higher levels in
the audio.
LFO Sweeps
To create a sweeping LFO node, select a node and click the LFO button. Additional LFO controls appear in the upper right corner as shown below:
You can set the period or speed of the sweep with the Period control. Smaller periods are faster sweeps, where the period is by default displayed in milliseconds. In addition to entering the speed directly, you can tap the "Tap Tempo" button to automatically set the speed to the rate that you've tapped the button.
The shape of the sweep can be set by clicking on the shape button -- toggling between various waveforms such as sine, square, and triangle to set the shape of the controlling sweep.
Note that the Options screen allows you to view and set the rate of the LFO in tempo (beats per minute) as opposed to milliseconds. Click on the Options button and set the LFO to display tempo. You can also have the LFO slider snap to integers of the tempo, allowing you for example, to easily go from full measure to half measure sweeps.
Finally, you'll want to set the position of the sweeping node -- the target destination for the sweep. A node can sweep in shape, frequency, and effect amount -- any parameter that can be set on a node can be used as a "target destination" for a sweep. For example, you might have a node that sweeps up and down in frequency, or one that sweeps to become wider and then more narrow.
To set a target destination, note that when you selected a filter and set it to LFO, an additional white circle appeared on the spectrum. That is your target filter -- you can position that filter in any location with any resonance or bandwidth, and your filter will sweep to that point. A red line connects a node with its target node, and a red dot on that line shows the current position of the modulation during playback.
Advanced LFOs
In addition to "simple" LFOs, Spectron provides an advanced mode that lets you further customize the behavior of the modulation. You can enter this advanced mode by clicking the "..." button next to the LFO shape
Resolution: lets you set a quantization or "staircasing" of the LFO signal. For smooth "continuous" modulations, set this control all the way to the right. At lower resolutions, you can achieve interesting stepped or staircased effects.
Pulse Width: This control only applies to the square wave and sample and hold LFO shapes, and controls the amount of time that the modulator wave is spending at its peaks. For example, at lower pulse widths these shapes are more often "off" or at zero.
Modulator: The advanced modulator controls let you modulate the modulations. For example, a simple LFO modulation might be a sine wave. It has a fixed frequency and amplitude that doesn't change over time. The advanced LFO lets you change that -- you can modulate your node with a sine wave as before, but also have an additional LFO that modulates the amplitude of that sine wave over time.
That's the basic idea behind "modulating the modulations" -- you can vary or modulate some aspect of a simple LFO shape.
Type: This controls what aspect of the simple LFO you want to modulate. You can modulate the amplitude of your simple LFO shape, the frequency, or the pulse width.
Period: This controls the rate of the advanced modulation. This is of course independent of the period of your simple LFO shape -- you could for example have a slowly sweeping sine wave for your simple LFO whose amplitude is modulated very quickly by your advanced LFO.
Shape: This sets the shape of your advanced LFO, which like the period is completely independent from the shape of your simple LFO.
Depth: The depth sets the amount of advanced modulation to apply to your simple LFO. For example, if you had an advanced LFO that was modulating the amplitude of your simple LFO, this control would let you set how much the amplitude of your simple LFO would be modulated.
Envelope Sweeps
Instead of sweeping to a timed LFO, you can sweep nodes based on the level of incoming audio.
To setup an envelope sweep on a filter, select a filter and click the Envelope button. Additional Envelope controls appear in the upper right corner as shown below:
Threshold: Sets the level at which the sweep will be triggered. Lower threshold will result in a sweep being triggered more often, as the level of the incoming audio will cross the threshold more often. Note that the threshold slider serves a dual purpose as a meter and a control, allowing you to see the level of the incoming audio as you adjust the threshold point.
Attack, Hold and Release: The attack sets the time that it takes the node to sweep to its destination after the threshold is exceeded, the hold specifies how long the node should be held at the destination, and the release sets the time it takes for the node to return to its original position after the level drops back down below the threshold.
Note that the threshold level is based on an RMS or averaging of the audio for a more natural and consistent effect. You can set the averaging time in the Spectron Engine Options tab by changing the Envelope RMS Time option.