alarm audio normalisation

pi/audio_handler.py

@@ -1,8 +1,10 @@
 """Audio alarm functions — WAV loading and PCM streaming."""
 
+import array
 import asyncio
 import json
 import logging
+import math
 import wave
 from pathlib import Path
 
@@ -32,15 +34,52 @@ def find_wav(path: Path | None = None) -> Path:
     return wavs[0]
 
 
+def _normalize_pcm(pcm: bytes, bits: int) -> bytes:
+    """Peak-normalize PCM data to 0 dBFS.
+
+    Supports 8-bit (unsigned) and 16-bit (signed) PCM.
+    Returns the original bytes unchanged if already at 0 dB or silent.
+    """
+    if bits == 16:
+        samples = array.array("h", pcm)          # signed 16-bit
+        peak = max(abs(s) for s in samples) if samples else 0
+        if peak == 0 or peak == 32767:
+            return pcm
+        scale = 32767 / peak
+        samples = array.array("h", (min(32767, max(-32768, int(s * scale))) for s in samples))
+    elif bits == 8:
+        samples = array.array("B", pcm)          # unsigned 8-bit, center=128
+        peak = max(abs(s - 128) for s in samples) if samples else 0
+        if peak == 0 or peak == 127:
+            return pcm
+        scale = 127 / peak
+        samples = array.array("B", (max(0, min(255, int((s - 128) * scale) + 128)) for s in samples))
+    else:
+        log.warning("Normalization not supported for %d-bit audio, skipping", bits)
+        return pcm
+
+    gain_db = 20 * __import__("math").log10(scale) if scale > 0 else 0
+    log.info("Normalized: peak %d → 0 dBFS (gain %.1f dB)", peak, gain_db)
+    return samples.tobytes()
+
+
 def read_wav(path: Path) -> tuple[bytes, int, int, int]:
-    """Read WAV file and return (pcm_data, sample_rate, channels, bits_per_sample)."""
-    with wave.open(str(path), "rb") as wf:
+    """Read WAV file, normalize to 0 dBFS, return (pcm_data, sample_rate, channels, bits)."""
+    try:
+        wf = wave.open(str(path), "rb")
+    except wave.Error as e:
+        raise ValueError(
+            f"{path.name}: unsupported WAV format ({e}). "
+            "Only 8/16-bit integer PCM is supported — no 32-bit float."
+        ) from e
+    with wf:
         sr = wf.getframerate()
         ch = wf.getnchannels()
         bits = wf.getsampwidth() * 8
         pcm = wf.readframes(wf.getnframes())
     log.info("WAV loaded: %dHz %dch %dbit, %.1fs, %d bytes",
              sr, ch, bits, len(pcm) / (sr * ch * (bits // 8)), len(pcm))
+    pcm = _normalize_pcm(pcm, bits)
     return pcm, sr, ch, bits