The Threeler is the name of a third-order VCF. Its main documentation is in this file:
Below are some sound clips.
The Threeler VCF in Mode 1 (third order lowpass). This clip illustrates some of the vocal and nonlinear distortion effects that the module can produce. The signal path used is a straightforward VCO-VCA-VCF one.
Several short clips demonstrating the Threeler in mode 2. Modulation of frequency and resonance along with operation above the oscillation threshold provide a wide variety of timbres including some interesting vocal sonorities.
Here is a demo of Threeler's mode 3. Several waveforms are sent sequentially to the filter via a wave scanner. The filter FM and Q are modulated by an AD+AR envelope generator.