feat: add tts effects module (bandpass + reverb + optional pitch)

effects.py

@@ -0,0 +1,71 @@
+import numpy as np
+from scipy.signal import butter, sosfiltfilt
+
+
+def _ensure_float32_mono(audio):
+    arr = np.asarray(audio, dtype=np.float32)
+    if arr.ndim > 1:
+        arr = arr.mean(axis=1).astype(np.float32)
+    return arr
+
+
+def apply_bandpass(audio, sr, low_hz=200, high_hz=7000, order=4):
+    arr = _ensure_float32_mono(audio)
+    nyq = 0.5 * sr
+    low = max(low_hz, 1) / nyq
+    high = min(high_hz, int(nyq) - 1) / nyq
+    if not (0 < low < high < 1):
+        return arr
+    sos = butter(order, [low, high], btype='band', output='sos')
+    return sosfiltfilt(sos, arr).astype(np.float32)
+
+
+def apply_reverb(audio, sr, wet=0.20, decay_ms=100, taps=4):
+    arr = _ensure_float32_mono(audio)
+    if wet <= 0 or decay_ms <= 0:
+        return arr
+    dry = max(0.0, 1.0 - wet)
+    out = dry * arr
+    gap = max(1, int(sr * (decay_ms / 1000.0) / taps))
+    gain = wet
+    for i in range(1, taps + 1):
+        delay = gap * i
+        gain *= 0.6
+        if delay >= len(arr):
+            break
+        padded = np.zeros_like(arr)
+        padded[delay:] = arr[:len(arr) - delay]
+        out += gain * padded
+    peak = float(np.max(np.abs(out))) if out.size else 0.0
+    if peak > 0.99:
+        out *= 0.99 / peak
+    return out.astype(np.float32)
+
+
+def apply_pitch(audio, sr, semitones=0):
+    arr = _ensure_float32_mono(audio)
+    if semitones == 0:
+        return arr
+    factor = 2.0 ** (semitones / 12.0)
+    n_out = int(round(len(arr) / factor))
+    if n_out <= 1:
+        return arr
+    src_idx = np.linspace(0, len(arr) - 1, num=n_out).astype(np.float32)
+    lo = np.floor(src_idx).astype(np.int64)
+    hi = np.clip(lo + 1, 0, len(arr) - 1)
+    frac = (src_idx - lo).astype(np.float32)
+    resampled = (1.0 - frac) * arr[lo] + frac * arr[hi]
+    return resampled.astype(np.float32)
+
+
+def process(audio, sr, bandpass=None, reverb=None, pitch_semitones=0):
+    out = _ensure_float32_mono(audio)
+    if bandpass is not None:
+        low, high = bandpass
+        out = apply_bandpass(out, sr, low, high)
+    if reverb is not None:
+        wet, decay_ms = reverb
+        out = apply_reverb(out, sr, wet=wet, decay_ms=decay_ms)
+    if pitch_semitones:
+        out = apply_pitch(out, sr, semitones=pitch_semitones)
+    return out