diff --git a/lib/ads/video/encode.ts b/lib/ads/video/encode.ts
index d4c89cd..54a3b21 100644
--- a/lib/ads/video/encode.ts
+++ b/lib/ads/video/encode.ts
@@ -336,6 +336,13 @@ export function posterArgs(inPath: string, outPath: string): string[] {
  * drift into describing different offers. A silent creative has no companion:
  * five seconds of silence would be recorded as an audio ad having played, and
  * the spec is explicit that silence never satisfies an audio slot.
+ *
+ * It carries the same mastering as the picture's own track. This is the file a
+ * music player asks for, and it is built from the raw narration rather than
+ * from the finished video, so without the filter here it keeps whatever level
+ * the voice came back at. That was the whole of the bug on this path: the
+ * video was brought up to streaming level while the audible spot, which is the
+ * only thing a radio or music listener ever gets, stayed near -29 dB.
  */
 export function audioCompanionArgs(inPath: string, outPath: string): string[] {
   return [
@@ -344,6 +351,8 @@ export function audioCompanionArgs(inPath: string, outPath: string): string[] {
     "-i",
     inPath,
     "-vn",
+    "-af",
+    LOUDNESS,
     "-c:a",
     "aac",
     "-profile:a",
diff --git a/tests/ads-video-compose-validate.test.ts b/tests/ads-video-compose-validate.test.ts
index afd27bd..91e6777 100644
--- a/tests/ads-video-compose-validate.test.ts
+++ b/tests/ads-video-compose-validate.test.ts
@@ -7,7 +7,7 @@ import {
   timeline,
 } from "@/lib/ads/video/compose";
 import type { VideoDesignSnapshot } from "@/lib/ads/video/snapshot";
-import { AAC_LC_CODEC, avcCodecString, GOP_FRAMES, hlsArgs, mp4Args, multivariantPlaylist, posterArgs } from "@/lib/ads/video/encode";
+import { AAC_LC_CODEC, audioCompanionArgs, avcCodecString, GOP_FRAMES, hlsArgs, mp4Args, multivariantPlaylist, posterArgs } from "@/lib/ads/video/encode";
 import {
   evaluateProbe,
   parseRational,
@@ -538,4 +538,21 @@ describe("loudness", () => {
     expect(a).toContain("-an");
     expect(a.join(" ")).not.toContain("loudnorm");
   });
+
+  it("masters the audible companion too, not only the picture", () => {
+    // The companion is built from the raw narration, not from the finished
+    // video, so it does not inherit the video track's mastering. A music
+    // player asks for this file and nothing else, which makes it the only
+    // thing most listeners ever hear.
+    const a = audioCompanionArgs("/tmp/narration.mp3", "/tmp/audio.m4a");
+    expect(a[a.indexOf("-af") + 1]).toBe("loudnorm=I=-16:TP=-1.5:LRA=11");
+  });
+
+  it("gives the companion the same target and ceiling as the video", () => {
+    // Two levels for one spot would mean the advert changed loudness when a
+    // listener moved between a video slot and an audio one.
+    const companion = audioCompanionArgs("/tmp/narration.mp3", "/tmp/audio.m4a");
+    const filter = companion[companion.indexOf("-af") + 1];
+    expect(narrated().join(" ")).toContain(filter);
+  });
 });