Here is the interview where it is mentioned: https://youtu.be/VwzNWvQF2ks?t=155

The filters were indeed not implemented using DSP building components or blocks but Chen says using “machine learning”. That can mean a lot unfortunately.

According to ASM: 144 recordings of waveforms (sawtooth, noise, …) through 11 different filter cut-off and resonance settings per filter (handpicked by the team) are used as reference material.

The idea was then to reproduce each of the 144 recordings with the least error possible. Instead of building their own filter signal chain by hand and calibrating that by ear, Chen let the computer automatically find the DSP design component chain and parameters whose output would get the closest to each of the recordings.