Hydrasynth Filters include:
Vocal filter
Multiple vowel order parameter
Formant parameter
from https://www.perfectcircuit.com/signal/asm-hydrasynth-interview
RG: The filter section also has a number of uncommon options—lowpass gate, vowel formants, and models inspired by classic synth designs. How did you settle on the filter types to be included?
GD: We mainly picked a bunch of filters we liked and wanted. I love the richness of a LPG. We needed to have a ladder style, both compensated and uncompensated. Ken “flux” Pierce of Fluxwithit.com introduced us to the Threeler filter, which is huge-sounding (I need to get an original one in my modular). Anyone with a modular should own one of those.
Chen came up with the vocal filter and asked if we wanted it…which we said of course…then I asked if we can arrange the vowels in different orders so he gave us a list of 8 different vowel orders. The interesting thing on the filters is how Chen made them. His background is first in math but then also AI. So we made recordings of the filters we liked, with a bunch of combinations of cutoff and resonance settings and he wrote a machine-learning program that analyzed the audio files and then recreated the profiles of them. So our filters are made via his Neural Network Filter modeling.