diff --git a/playbooks/nh3-dev-install-sox.yaml b/playbooks/nh3-dev-install-sox.yaml
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+# sox on nh3-dev — requested by yt-voice-clipper-dev 2026-09-09 for a
+# subtractive-denoise audition (`sox noisered`) against DeepFilterNet 3 and
+# ffmpeg anlmdn. Binary only, no config.
+steps:
+  - name: Install sox (+ the mp3/flac format handlers)
+    shell: DEBIAN_FRONTEND=noninteractive apt-get install -y -q sox libsox-fmt-all
+    sudo: true
+    creates: /usr/bin/sox
+
+verify:
+  - name: sox on PATH and reports a version
+    shell: sox --version
+    changed_when: "false"
+
+  - name: noisered effect is present (the reason for the ask)
+    shell: sox --help 2>&1 | grep -qw noisered
+    changed_when: "false"