Demonstrating some artifacts the stock high-pass filter in pure data generates when tasked with extremely low frequencies. Beyond just being interesting sounds, these artifacts are interesting because the hip~ appears in all kinds of abstractions and may be responsible for noises in your patch.
(The audio in this video contains ultra-high pitches in the left channel only; mind the volume – though I think Vimeo's optimized some of them away)
3 classes of artifacts:
1. "squishy" / "sparkly" "arpeggios" (these are possibly reflections)
2. very high harmonics / partials above the input frequency
3. static whine pitch related to the sampling rate 689Hz ~= 44100/64
