Inspired by modular “Divide by N Comparators” while taking things drastically further, the Pulse-Width Pitch Applicator & Divider does a lot of things to incoming audio.
It can convert it to a pulse-wave for a synth-y-er sound, act as a divider to drop its pitch, and modulate a pulse-width limiter for the audio effect equivalent of pulse-width modulation. Incoming samples/sounds go out sounding like something in-between a recording and a synthesizer, especially when followed by filters and such.
While it’s squaring off incoming audio, it can also detect the pitch, outputting pitch cv (1v/oct) for controlling oscillators, matching the frequency of the audio. There are noise reduction, window size, octave, and even tuning controls for helping you get a desired pitch response. The detection is analog-modeled, so, for tracking complicated sounds like voice or guitars, you’ll want adjust your style to suit this module’s strengths. Nonetheless, you can get some really fun results by performing a synth sound without a keyboard.
In addition, there’s an internal envelope follower which gets compared to an adjustable threshold – as a result, a gate signal is created when incoming audio is loud enough. Connect this gate output to an envelope generator (or use it as a percussion trigger) and now you have everything you need to transform audio into a synthesizer.
While it was designed for audio, sending synthesized sounds into it is a great use. You can derive a 2nd signal to make a stereo pair, use a large window to create something in between a delay and a harmonizer, and you can get really creative with modulation to turn this into an unusual effect in its own right.
This may give you some ideas: