diff --git a/firmware/src/app/ui.c b/firmware/src/app/ui.c
index 5edca39..cfe6e19 100644
--- a/firmware/src/app/ui.c
+++ b/firmware/src/app/ui.c
@@ -41,22 +41,25 @@ static const char *const KNOB_LABEL[NVIEWS][4] = {
 /* the screen's colours: the cover of Ambient 1: Music for Airports (1978), as the web app and the site.
  * The map's paper, its ink; the land's greens for the pad (the chord) and the scale, its rivers for the
  * bells; the bass and the pulse in darker inks. Each layer has a pale tint for the shapes at rest. */
-#define K_BG RGB(246, 238, 181)
-#define K_PANEL RGB(255, 251, 224)
-#define K_LINE RGB(208, 214, 150)
-#define K_DIM RGB(112, 106, 58)
-#define K_TEXT RGB(29, 27, 2)
-#define K_ACC RGB(64, 128, 124)          /* the accent: the page, the knob being turned, a message's word */
-#define K_BELL RGB(84, 153, 149)
-#define K_BELL_T RGB(176, 214, 206)
-#define K_PAD RGB(112, 142, 62)
-#define K_PAD_T RGB(208, 220, 146)
-#define K_PULSE RGB(70, 66, 28)
-#define K_PULSE_T RGB(214, 214, 160)
-#define K_BASS RGB(138, 128, 52)
-#define K_BASS_T RGB(222, 218, 160)
-#define K_FROST RGB(60, 132, 160)
-#define K_FROST_T RGB(170, 210, 216)
+/* DoomBox crypt palette: near-black stone, blood red, bone text */
+#define K_BG RGB(12, 6, 8)
+#define K_PANEL RGB(26, 10, 14)
+#define K_LINE RGB(62, 22, 28)
+#define K_DIM RGB(140, 96, 92)
+#define K_TEXT RGB(232, 220, 206)
+#define K_ACC RGB(220, 38, 38)           /* the accent: the page, the knob being turned, a message's word */
+#define K_BELL RGB(239, 68, 68)
+#define K_BELL_T RGB(96, 28, 34)
+#define K_PAD RGB(168, 42, 56)
+#define K_PAD_T RGB(70, 20, 30)
+#define K_PULSE RGB(214, 190, 170)
+#define K_PULSE_T RGB(60, 36, 36)
+#define K_BASS RGB(190, 120, 40)
+#define K_BASS_T RGB(70, 40, 20)
+#define K_FROST RGB(80, 170, 190)
+#define K_FROST_T RGB(24, 56, 66)
+#define K_SIGIL RGB(40, 12, 16)
+#define K_SIGIL_HI RGB(74, 16, 22)
 
 static struct {
     uint8_t view;
@@ -664,10 +667,61 @@ static void polar(int32_t cx, int32_t cy, float r, int i, int n, int32_t *x, int
     *y = cy - (int32_t)(sy + (sy < 0.0f ? -0.5f : 0.5f));
 }
 
+/* DoomBox: a dim pentagram sigil behind the garden */
+static void cv_line_thick(int32_t x0, int32_t y0, int32_t x1, int32_t y1, int32_t r, uint16_t c)
+{
+    int32_t dx = (x1 > x0) ? (x1 - x0) : (x0 - x1);
+    int32_t dy = (y1 > y0) ? (y1 - y0) : (y0 - y1);
+    int32_t sx = (x0 < x1) ? 1 : -1;
+    int32_t sy = (y0 < y1) ? 1 : -1;
+    int32_t err = dx - dy;
+
+    for (;;) {
+        cv_disc(x0, y0, r, c);
+        if (x0 == x1 && y0 == y1)
+            break;
+        {
+            int32_t e2 = err * 2;
+            if (e2 > -dy) {
+                err -= dy;
+                x0 += sx;
+            }
+            if (e2 < dx) {
+                err += dx;
+                y0 += sy;
+            }
+        }
+    }
+}
+
+static void draw_sigil(void)
+{
+    int32_t i;
+    int32_t x, y;
+
+    for (i = 0; i < 72; i++) {
+        polar(CX, CY, 72.0f, i, 72, &x, &y);
+        cv_disc(x, y, 1, K_SIGIL);
+        polar(CX, CY, 68.0f, i, 72, &x, &y);
+        cv_disc(x, y, 1, K_SIGIL);
+    }
+
+    for (i = 0; i < 5; i++) {
+        int32_t i0 = (i * 2) % 5;
+        int32_t i1 = (i0 + 2) % 5;
+        int32_t x0, y0, x1, y1;
+
+        polar(CX, CY, 66.0f, i0, 5, &x0, &y0);
+        polar(CX, CY, 66.0f, i1, 5, &x1, &y1);
+        cv_line_thick(x0, y0, x1, y1, 1, K_SIGIL_HI);
+    }
+}
+
 static void draw_ring(void)
 {
     uint32_t abs_pool = pool_abs(), chord = 0;
     int i, l;
+    draw_sigil();
     for (i = 0; i < EN_NPAD; i++)
         chord |= 1u << (en_chord[i] % 12u);
     for (l = 0; l < EN_NLOOP; l++) {
diff --git a/firmware/src/dsp/amb.c b/firmware/src/dsp/amb.c
index 185b56e..4b468d5 100644
--- a/firmware/src/dsp/amb.c
+++ b/firmware/src/dsp/amb.c
@@ -2,6 +2,7 @@
 /* The instrument (amb.h). One compilation unit, -O2. */
 #include "amb.h"
 #include "fastmath.h"
+#define DOOM_DRIVE 1.6f                      /* DoomBox saturation drive */
 
 #ifdef EN_HOST
 #define EN_POOL
@@ -1702,6 +1703,8 @@ static void render_chunk(int32_t *out, uint32_t n, float gain)
         reverb((rsend[j] * rg + (el + er + xl + xr) * 0.35f * rev_send) * 0.8f, &wl, &wr);
         l = (mixl[j] + 0.75f * el + 0.3f * xl + 1.3f * wl) * 0.36f * gain;
         r = (mixr[j] + 0.75f * er + 0.3f * xr + 1.3f * wr) * 0.36f * gain;
+        l = fm_tanhf(l * DOOM_DRIVE) * (1.0f / DOOM_DRIVE);   /* DoomBox: tape-style saturation, unity at low level */
+        r = fm_tanhf(r * DOOM_DRIVE) * (1.0f / DOOM_DRIVE);
         out[2 * j] = (int32_t)(fm_tanhf(l) * 8300000.0f);
         out[2 * j + 1] = (int32_t)(fm_tanhf(r) * 8300000.0f);
     }