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diff --git a/doc/HOWTO.md b/doc/HOWTO.md
index 097f2fa..768e51d 100644
--- a/doc/HOWTO.md
+++ b/doc/HOWTO.md
@@ -242,6 +242,21 @@ audio_shutdown();
 
 See `doc/TRACKER.md` for music system.
 
+### Regenerating .spec Files
+
+Converts `.wav`/`.aif` files from `tools/originals/` into `.spec` files in `workspaces/main/music/`.
+
+```bash
+# Build spectool first (requires DEMO_BUILD_TOOLS=ON)
+cmake -S . -B build -DDEMO_BUILD_TOOLS=ON
+cmake --build build -j4 --target spectool
+
+# Generate all spectrograms
+./scripts/gen_spectrograms.sh
+```
+
+Requires `ffmpeg` for `.aif` input files. Output uses v2 format (OLA, Hann, hop=256).
+
 ---
 
 ## Assets