diff --git a/simulator/static/app.js b/simulator/static/app.js
index 92bee4f..a0a5096 100644
--- a/simulator/static/app.js
+++ b/simulator/static/app.js
@@ -960,10 +960,25 @@ function fadeVolume(el, to, ms, done) {
   }, 30);
 }
 
-// The current altitude's soundtrack url (the ring carries each scale's `audio`).
+// Fallback per-scale soundtrack paths, used when the ring from /api/ring lacks the
+// `audio` field (e.g. a server process started before the audio field existed).
+// Mirrors simulator/build_pool_manifest.py SCALE_AUDIO — the 5 scales + files are
+// fixed, committed facts, so this keeps audio working without a server restart.
+const SCALE_AUDIO_FALLBACK = {
+  cosmos: "cosmos/pillars.loop.mp3",
+  orbit: "orbit/spaceamb.loop.mp3",
+  coast: "coast/waves.loop.mp3",
+  reef: "reef/soundscape.loop.mp3",
+  abyss: "abyss/whale.loop.mp3",
+};
+
+// The current altitude's soundtrack url: the ring's `audio` field, else the
+// scale-id fallback above.
 function soundtrackUrl() {
   const s = ring && ring.scales[ringIndex];
-  return s && s.audio ? "/media/audio/" + s.audio : null;
+  if (!s) return null;
+  const a = s.audio || SCALE_AUDIO_FALLBACK[s.id];
+  return a ? "/media/audio/" + a : null;
 }
 
 // Load `url` into the single element and fade it in. Call this SYNCHRONOUSLY from
diff --git a/tests/test_e2e_audio.py b/tests/test_e2e_audio.py
index 1fd86de..2111e89 100644
--- a/tests/test_e2e_audio.py
+++ b/tests/test_e2e_audio.py
@@ -101,6 +101,26 @@ def test_audio_before_video_stays_audio_only(page):
     page.wait_for_selector("#black:not(.hidden)")       # still blanked
 
 
+def test_audio_then_video_leaves_both_on(page):
+    _toggle(page, "audio")                             # audio first
+    page.wait_for_function("!document.getElementById('aud').paused")
+    _toggle(page, "visual")                            # then video
+    page.wait_for_selector("#black.hidden", state="attached")   # video showing
+    assert page.is_checked("#audio") is True
+    assert page.evaluate("!document.getElementById('aud').paused") is True   # audio still plays
+
+
+def test_soundtrack_fallback_when_ring_lacks_audio(page):
+    # simulate a stale server whose /api/ring omits the per-scale `audio` field;
+    # the client falls back to the scale-id soundtrack map so audio still plays
+    page.evaluate("ring.scales.forEach(s => { delete s.audio; })")
+    _toggle(page, "audio")
+    page.wait_for_function(
+        "(() => { const a = document.getElementById('aud');"
+        " return a.src.includes('/media/audio/cosmos/') && !a.paused; })()"
+    )
+
+
 def test_video_off_blanks_after_being_on(page):
     _toggle(page, "visual")                            # on
     page.wait_for_selector("#black.hidden", state="attached")