Vellum

The eight delay lines behind the tail sit at deliberately non-harmonic lengths, so they never re-align into a pitch — the faint metallic ring that gives most digital reverbs away. Three separate stages of diffusion then break the echoes apart: eight to sixteen allpass filters at the input, another nested inside every delay line multiplying density on every pass, and a shaped early cluster. Measured on the finished tail, its crest factor lands in the same range as Gaussian noise. By that measure it is as diffuse as a reverb can be.

Damping happens inside the feedback loop rather than at the input, so a dark setting keeps getting darker as it decays — the way absorption behaves in a real room, instead of one EQ curve smeared across the whole tail. And you can sweep any control while audio is playing without it warbling. Moving a delay line's read position is a pitch shift by definition; Vellum crossfades between fixed taps instead, and a test measures the tail's pitch before and after every change to keep it that way.