Echo Train

Where a delay's repeats land and how loud they are, as pure maths: tap times and levels from time/feedback/mix, the L-R alternation of a cross-coupled ping-pong pair, an audibility floor and a tap cap, a 60 dB decay time, beat-grid ticks for a tempo, and a time/level axis with forward and inverse mappings. Derived from the shipped delay graphs and pinned against sample-accurate simulations of them. No React, no DOM — testable in Node and safe to draw with on the server.