Describe the Flanger's thin line and its fading trail (#398)

- Sounds: the response is one thin line. Behind the Flanger's comb a
  faint trail fades with age, and the line fades out where its teeth
  pass faster than an eye follows.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Sounds.md

@@ -1106,15 +1106,19 @@ stays.
 - **The devices** (#398): in the graph a Phaser is a plate of 760x280 graph units in mustard, a
   Flanger one of 680x280 in steel blue, their inputs on the left and their output on the right.
   - **The screen** draws what is left of each frequency, 20 Hz to 20 kHz in octaves, +12 to -36
-    dB: the notches of the Phaser, the comb of the Flanger, and the peaks feedback rings. A comb
-    finer than the screen fills the columns it runs through instead of aliasing. It uses the
+    dB: the notches of the Phaser, the comb of the Flanger, and the peaks feedback rings, as one
+    thin line. A comb finer than the screen zigzags over the columns it runs through instead of
+    aliasing. It uses the
     allpasses, the feedback and the delay of the worklet, at 48 kHz: the unit tests find the same
     dB as the worklet on a sine, within 0.005 dB.
-  - The Flanger's comb is reckoned exactly per column, not read at points, and blurred over the
-    delays of the last 1/20 s (#398). High up its teeth pass faster than frames are drawn, and
-    sharp frames of them flickered. There they become a calm band from the deepest notch to the
-    highest peak, while further down, where the eye can follow them, they stay sharp. The edges
-    are drawn as smooth lines, not as one rectangle per column.
+  - The Flanger's comb is reckoned exactly, through the ends of each column and the peaks and
+    notches in it, not read at points (#398). Behind the line a faint **trail** shows what it swept
+    over the last 1/20 s, and over the last 1/40 s once more, so it fades with age. High up its
+    teeth pass faster than frames are drawn, and a sharp line of them would flicker. Where they
+    move more than a quarter of a tooth within the trail, the line fades out, and from half a
+    tooth on only the trail is left there: a calm band from the deepest notch to the highest peak.
+    Where the eye can follow the teeth, the line stays sharp and moves. A Flanger that stands
+    still has no trail.
   - Under it a **lane** shows where that goes over the first seconds of a sound: the Phaser's turn
     in Hz, the Flanger's delay in ms (up to 2.5, 5, 10 or 20). A light runs over the lane in real
     time and the response above is drawn where it is, so the notches swirl and the comb jets as