greg-randall · February 19, 2025 00:52 · Feb 19, 2025
diff --git a/norm.py b/norm.py
@@ -0,0 +1,126 @@
+"""
+This tool normalizes the loudness of MP3 audio files to a consistent level. Here's how to use it:
+
+Run the script with a directory path: python script.py /path/to/mp3s
+By default, it sets audio to -14 LUFS (loudness units) and prevents clipping at -0.1dB
+It creates new files prefixed with "processed_" unless you use --overwrite
+You can customize the target loudness with --target-lufs and peak limit with --threshold-db
+
+The tool analyzes each MP3 file, adjusts its volume to the target loudness, applies a limiter to prevent distortion, and saves the processed version.
+"""
+
+
+import os
+from pydub import AudioSegment
+from pathlib import Path
+import pyloudnorm as pyln
+import soundfile as sf
+import numpy as np
+
+def process_audio(input_path, target_lufs=-14, threshold_db=-0.1, overwrite=False):
+    """
+    Process audio file by:
+    1. Converting to WAV for processing
+    2. Normalizing to target LUFS
+    3. Applying hard limiter
+    4. Exporting back to MP3
+    
+    Args:
+        input_path (str): Path to the input audio file
+        target_lufs (float): Target loudness in LUFS
+        threshold_db (float): Maximum allowed amplitude in dB
+        overwrite (bool): If True, replace original file
+    """
+    input_path = Path(input_path)
+    if overwrite:
+        output_path = input_path
+        temp_path = input_path.parent / f".temp_{input_path.name}"
+    else:
+        output_path = input_path.parent / f"processed_{input_path.name}"
+        temp_path = output_path
+
+    try:
+        # Load the audio file and immediately convert to WAV in memory
+        audio = AudioSegment.from_mp3(input_path)
+
+        # Get the audio data as numpy array for LUFS processing
+        samples = np.array(audio.get_array_of_samples())
+        normalized_samples = samples / (1 << (8 * audio.sample_width - 1))
+
+        # Measure LUFS
+        meter = pyln.Meter(audio.frame_rate)
+        current_loudness = meter.integrated_loudness(normalized_samples)
+
+        # Calculate and apply loudness adjustment
+        loudness_gain = target_lufs - current_loudness
+        audio = audio.apply_gain(loudness_gain)
+
+        # Apply limiter (still in WAV format)
+        if audio.dBFS > threshold_db:
+            reduction_db = threshold_db - audio.dBFS
+            audio = audio.apply_gain(reduction_db)
+
+        # Export to temporary file first
+        audio.export(str(temp_path), format="mp3", parameters=["-q:a", "0"])
+
+        if overwrite:
+            # Atomic replace of original file
+            temp_path.replace(output_path)
+
+        print(f"Processed {input_path.name}:")
+        print(f"  - Original loudness: {current_loudness:.1f} LUFS")
+        print(f"  - Applied gain: {loudness_gain:.1f} dB")
+        if audio.dBFS > threshold_db:
+            print(f"  - Limited peaks to {threshold_db} dB")
+
+    except Exception as e:
+        # Clean up temp file if it exists
+        if temp_path.exists():
+            temp_path.unlink()
+        print(f"Error processing {input_path}: {str(e)}")
+
+def process_directory(directory_path, target_lufs=-14, threshold_db=-0.1, overwrite=False):
+    """
+    Process all MP3 files in a directory.
+    
+    Args:
+        directory_path (str): Path to the directory containing MP3 files
+        target_lufs (float): Target loudness in LUFS
+        threshold_db (float): Maximum allowed amplitude in dB
+        overwrite (bool): If True, replace original files
+    """
+    directory = Path(directory_path)
+    if not directory.exists():
+        print(f"Directory {directory_path} does not exist!")
+        return
+
+    mp3_files = list(directory.glob("*.mp3"))
+    if not mp3_files:
+        print("No MP3 files found in the directory!")
+        return
+
+    print(f"Found {len(mp3_files)} MP3 files to process...")
+    print(f"Target loudness: {target_lufs} LUFS")
+    print(f"Peak limit: {threshold_db} dB")
+    print(f"Overwrite mode: {'enabled' if overwrite else 'disabled'}")
+    print()
+
+    for mp3_file in mp3_files:
+        process_audio(str(mp3_file), target_lufs, threshold_db, overwrite)
+
+    print("\nProcessing complete!")
+
+if __name__ == "__main__":
+    import argparse
+
+    parser = argparse.ArgumentParser(description="Process audio files with minimal quality loss")
+    parser.add_argument("directory", help="Directory containing MP3 files")
+    parser.add_argument("--target-lufs", type=float, default=-14,
+                      help="Target loudness in LUFS (default: -14)")
+    parser.add_argument("--threshold-db", type=float, default=-0.1,
+                      help="Maximum allowed amplitude in dB (default: -0.1)")
+    parser.add_argument("--overwrite", action="store_true",
+                      help="Replace original files instead of creating new ones")
+
+    args = parser.parse_args()
+    process_directory(args.directory, args.target_lufs, args.threshold_db, args.overwrite)
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