Mod Envelope
You will find many similarities between the amp and mod envelopes. Katla features five mod envelopes controlled through a single interface. Their timing can be offset with the key-tracking knob, and they can be looped by pressing the Loop button.
The mod envelope can be routed to five destinations: phase distortion, filter cutoff, LFO rate, Rökkur, and Rústir.
Phase Distortion
Section titled “Phase Distortion”Phase distortion reshapes a waveform’s phase angle to create new harmonics. Many users are familiar with pulse-width modulation, where the duty cycle of a pulse wave is shifted to alter its harmonic content. Phase distortion applies a similar idea more broadly, bending the phase of any waveform to generate new timbres. Pushing the slider upward introduces phase distortion, while pushing it downward inverts its direction. When applied to an external audio source, phase distortion will introduce a phaser.
Internally Katla’s control signals make use of wavefolding. This means that when the envelope or LFO pushes a parameter beyond its limits, the modulation inverts direction and begins to reduce or increase the value instead. In the Mod Envelope, this behavior applies to the Phase Distortion, Rökkur, and Rústir destinations.
Filter Cutoff
Section titled “Filter Cutoff”Pushing the slider upward increases the filter cutoff frequency, while pushing it downward reduces it.
LFO Rate
Section titled “LFO Rate”Increases or decreases the LFO rate.
Rökkur
Section titled “Rökkur”Rökkur is Katla’s stereo spreader. Modulating this parameter introduces movement in the stereo field, and when key-tracking is enabled, each note is panned independently. Pushing the slider upward applies panning according to Rökkur’s internal logic, while pushing it downward reverses the panning order. When adjusting the Rökkur slider in the Katla section, voice 1 remains centered; however, modulating Rökkur with the Mod Envelope introduces stereo movement to voice 1 as well. As mentioned earlier, this control signal is wavefolded when pushed beyond its upper or lower limits, causing its direction to invert.
Rústir
Section titled “Rústir”Rústir is Katla’s wavefolder. Pushing the slider upward increases wavefolding, while pushing it downward reduces it. As mentioned earlier, this control signal is itself wavefolded when pushed beyond its upper or lower limits, causing its direction to invert.