Dual Undula Filter Core Complex Oscillator

Larix Elektro Dual Undula

The Dual Undula from Larix Elektro is a dual VCO/filter with internal modulation, wavefolding, bipolar VCAs, and adjustable left/right or mid/side processing. It both generates sounds on its own and acts as a processor for external signals. The faceplate is mirrored, with each side providing the same functionality as the other. The oscillators use a highly resonant filter as their sine wave cores. A resonant filter uses feedback to produce emphasis at its cutoff frequency, creating the distinctive sound of a filter sweep. This control is often marked as resonance, Q, or emphasis. On the Dual Undula, this is marked Osc ctrl (Q). As the resonance increases, instabilities within the circuit cause it to oscillate, creating a sine wave. The frequency controls on the Dual Undula Oscillators change the cutoff frequency of the filter and the pitch of the sine wave oscillations. In order to use the module as a VCO, make sure to put the Q knob past the dot on the panel. Moving this control further clockwise increases the resonance and colors the sound further. An external audio input is available on both channels, allowing it to act as a more traditional filter. Patching into this jack inserts the signal into the feedback loop. Of course, you're free to run external signals into the audio input of a self-oscillating channel. The module doesn't just output sine wave tones from the oscillator's main output, flipping the associated switch converts the output from a sine to a square waveform. The oscillator outputs then run into a voltage controlled wavefolder. Patching into the Ext In jacks on the wavefolder sums an external signal with the oscillator output.

From there, both wavefolders pass into the center dual VCA and processor section. The VCAs are bipolar. In the center, the outputs are off, turning to offset or mod attenuverters to the right increases the amplitude positively. Turning to the left also increases the amplitude, but inverts the phase, negatively increasing the amplitude. Bipolar VCAs, also known as four-quadrant multipliers, are also used for ring modulation when sent two audio rate signals. The switch in the center of the module selects between Left/Right and Mid/Side processing. Left/right mode hard pans each oscillator to its respective side in the stereo field, and acts as two independent VCA channels. Mid/side processing is more commonly found in the world of recording, mixing, and mastering than in Eurorack. The mid part of the processing contains the parts of the audio signal that are the same, the side includes the other parts of the audio that are different. The Dual Undula Oscillator also includes an LFO and attack/decay envelope. Both parts of the modulation section are freely patchable, but the square output is normalled into the trig input on the envelope. While the layout of Larix Elektro's Dual Undula Oscillator is reminiscent of many 259-inspired complex oscillators, the complexity contained in the module comes in a different variety than you might expect, bringing new avenues of musical expression to any system.

Dual Undula Features

• Dual filter/oscillator with bipolar VCAs, wavefolding, and modulation
• Uses highly resonant filters to create sine wave oscillations
• External audio inputs on the filter sections, wavefolders, and VCAs
• Output VCAs either act independently or as mid/side processing pair
• LFO and A/D envelope provide internal modulation
• Switchable sine and square outputs
• Extensive normalization