From 69fd884aaec5523871696149cd39aff6b10c9397 Mon Sep 17 00:00:00 2001
From: skal <pascal.massimino@gmail.com>
Date: Fri, 6 Feb 2026 18:31:14 +0100
Subject: feat(audio): Add RMS normalization to spectool for consistent sample
 loudness
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IMPLEMENTATION:
- Added --normalize flag to spectool analyze command
- Default target RMS: 0.15 (customizable via --normalize [rms])
- Two-pass processing: load all PCM → calculate RMS/peak → normalize → DCT
- Peak-limiting safety: prevents clipping by limiting scale factor if peak > 1.0
- Updated gen_spectrograms.sh to use --normalize by default

ALGORITHM:
1. Calculate original RMS and peak of input audio
2. Compute scale factor to reach target RMS (default 0.15)
3. Check if scaled peak would exceed 1.0 (after windowing + IDCT)
4. If yes, reduce scale factor to keep peak ≤ 1.0 (prevents clipping)
5. Apply scale factor to all PCM samples before windowing/DCT

RESULTS:
Before normalization:
  - RMS range: 0.054 - 0.248 (4.6x variation, ~13 dB)
  - Some peaks > 1.0 (clipping)

After normalization:
  - RMS range: 0.049 - 0.097 (2.0x variation, ~6 dB)  ✅ 2.3x improvement
  - All peaks < 1.0 (no clipping)  ✅

SAMPLES REGENERATED:
- All 14 .spec files regenerated with normalization
- High dynamic range samples (SNARE_808, CRASH_DMX, HIHAT_CLOSED_DMX)
  were peak-limited to prevent clipping
- Consistent loudness across all drum and bass samples

GITIGNORE CHANGE:
- Removed *.spec from .gitignore to track normalized spectrograms
- This ensures reproducibility and prevents drift from source files

handoff(Claude): RMS normalization implemented and working. All samples now have consistent loudness with no clipping.
---
 scripts/gen_spectrograms.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

(limited to 'scripts/gen_spectrograms.sh')

diff --git a/scripts/gen_spectrograms.sh b/scripts/gen_spectrograms.sh
index 7eb6bdc..a5c1510 100755
--- a/scripts/gen_spectrograms.sh
+++ b/scripts/gen_spectrograms.sh
@@ -49,7 +49,7 @@ process_file() {
     fi
 
     echo "Generating spectrogram: ${base_name} -> ${output_name}.spec"
-    "${SPECTOOL_PATH}" analyze "$file_to_process" "$spec_file"
+    "${SPECTOOL_PATH}" analyze "$file_to_process" "$spec_file" --normalize
 }
 
 # Find and process all audio files
-- 
cgit v1.2.3