Morphing Filter Bank

Voltage Controlled Formant Filter

The Morphing Filter Bank is a unique take on formant filtering. Four fixed frequency resonant bandpass filters are tied together in a feedback loop. Modulating the gain of this feedback loop, via the voice control, causes the resonant peak of each bandpass filter to split into two, and these two new peaks then diverge across the frequency spectrum.

The Morphing Filter Bank is a versatile tool that can add anything from prominent vocalizations to subtle timbral shifts to patches. A variable notch output is provided alongside the bandpass outputs. When the voice control is at zero, the frequency response of the variable notch output is flat, meaning it allows all frequencies to pass unaltered. Modulating the voice control increases the width and depth of the notch, adding an almost phaser-like sound along with the formant filtering. Because a notch filter allows both high and low frequencies to pass, this output is great for adding motion to bass patches.

The Morphing Filter Bank is a part of a limited release series. Each module was assembled by hand and thoroughly tested in Brooklyn, New York. The audio signal path utilizes hand matched high quality film capacitors. Two different versions of the module are available. One utilizes an OTA for the voice control circuitry, while the other utilizes Vactrols. The OTA variant responds faster to incoming CV, providing better performance with audio rate modulation. The OTA also adds subtle character to what would otherwise be a very clean sounding filter. The Vactrol variant responds slower to incoming CV and provides a much cleaner sound for the filter. The Vactrol variant is also able to achieve much deeper levels of modulation and can push the bandpass filters into self oscillation with proper adjustment of the trimmer on the PCB.

https://www.shkrjn.com/modules/p/morphing-filter-bank