Add TTS audiobook generator with dual-voice effect

Generates Russian audiobooks from ASFR stories using Silero TTS v5.
Narrator voice (eugene) for prose, robotic voice for system errors.

- tts/tts_silas.py: generator script with stress accentor + robotic effect
- tts/README.md: documentation
- .gitignore: exclude output WAV files

.gitignore

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+tts/output/

tts/README.md

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+# TTS — Audio Generation for ASFR Stories
+
+## What
+
+Generates audiobooks from story files using **Silero TTS v5** (Russian). Two voices:
+- **Narrator** — male voice (`eugene`) for the story prose
+- **Cyborg voice** — same voice with robotic effect (pitch shift + ring modulation + bitcrush) for system error messages (`ОШИБКА:`, `ПРЕДУПРЕЖДЕНИЕ:`)
+
+## Setup
+
+```bash
+uv add torch torchaudio silero silero-stress soundfile librosa
+```
+
+## Usage
+
+```bash
+# Generate Silas audiobook
+uv run tts/tts_silas.py Silas.md
+
+# Generate any story
+uv run tts/tts_silas.py Logan.md
+```
+
+Output goes to `tts/output/`:
+- `<name>_full.wav` — complete audiobook
+- `<name>_demo.wav` — first 4 segments (~1 min)
+
+## Voice Options
+
+Available Silero v5_ru voices:
+- `aidar` — deep male (can be monotone)
+- `eugene` — male, more expressive intonation ← default
+- `baya` — female, soft
+- `kseniya` — female, clear
+- `xenia` — female, calm
+
+Change `SPEAKER` in `tts_silas.py` to switch voices.
+
+## Robotic Effect
+
+System messages get these audio effects:
+- Pitch shift: -4 semitones (deeper, more mechanical)
+- Ring modulation: 50 Hz carrier (metallic timbre)
+- Bitcrush: 200 levels (digital distortion)
+
+Parameters in `make_robotic()` can be tuned.
+
+## Known Issues
+
+- Silero can misplace Russian word stress on complex sentences
+- Long paragraphs are split at sentence boundaries
+- Robotic effect uses librosa which has deprecation warnings (harmless)

tts/tts_silas.py

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+#!/usr/bin/env python3
+"""
+TTS generator for ASFR stories with dual-voice effect.
+
+Uses Silero TTS v5 (Russian) with the 'aidar' voice for narration,
+applies a robotic effect (pitch shift + ring modulation + bitcrush)
+to system error messages (lines starting with ОШИБКА:/ПРЕДУПРЕЖДЕНИЕ:).
+
+Usage:
+    uv run tts/tts_silas.py              # generate Silas audiobook
+    uv run tts/tts_silas.py <file.md>    # generate for any story
+
+Output:
+    tts/output/<name>_full.wav   — full audiobook
+    tts/output/<name>_demo.wav   — first 4 segments
+
+Requirements (installed via uv):
+    torch, torchaudio, silero, silero-stress, soundfile, librosa
+"""
+
+import re
+import sys
+import torch
+import soundfile as sf
+import numpy as np
+from pathlib import Path
+
+# === Config ===
+MODEL_ID = "v5_ru"
+SPEAKER = "eugene"          # male, more expressive intonation
+USE_STRESS = True              # silero-stress for correct word emphasis
+SAMPLE_RATE = 48000
+MAX_CHARS = 450             # silero works best with short segments
+
+# === Load model ===
+def load_model():
+    device = torch.device("cpu")
+    model, _ = torch.hub.load(
+        repo_or_dir="snakers4/silero-models",
+        model="silero_tts",
+        language="ru",
+        speaker=MODEL_ID,
+    )
+    model.to(device)
+    return model
+
+def apply_stress(text):
+    """Add stress marks for correct pronunciation using silero-stress."""
+    try:
+        from silero_stress import StressAccentor
+        accentor = StressAccentor()
+        return accentor.apply_stress(text)
+    except Exception:
+        return text
+
+# === Robotic effect ===
+def make_robotic(audio, sr, pitch_shift=-4, ring_freq=60, bit_depth=200):
+    """Transform normal voice into robotic/cyborg voice."""
+    import librosa
+    audio = librosa.effects.pitch_shift(audio, sr=sr, n_steps=pitch_shift)
+    t = np.linspace(0, len(audio) / sr, len(audio))
+    ring = np.sin(2 * np.pi * ring_freq * t)
+    audio = audio * (0.75 + 0.25 * ring)
+    audio = np.round(audio * bit_depth) / bit_depth
+    audio = audio / np.max(np.abs(audio)) * 0.9
+    return audio
+
+# === Split text into segments ===
+def parse_segments(text):
+    """Split text into (type, text) pairs. System errors get 'robot' type."""
+    text = re.sub(r"^---\n.*?---\n", "", text, flags=re.DOTALL)
+    text = text.strip()
+    
+    segments = []
+    paragraphs = text.split("\n\n")
+    
+    for para in paragraphs:
+        para = para.strip()
+        if not para:
+            continue
+        lines = para.split("\n")
+        is_system = all(
+            line.strip().startswith(("ПРЕДУПРЕЖДЕНИЕ:", "ОШИБКА:"))
+            for line in lines if line.strip()
+        )
+        if is_system:
+            clean = "\n".join(line.strip().lstrip("—").strip() for line in lines if line.strip())
+            segments.append(("robot", clean))
+        else:
+            segments.append(("normal", para))
+    
+    return segments
+
+# === Split long text for silero ===
+def split_long(text, max_chars=MAX_CHARS):
+    parts = []
+    remaining = text
+    while remaining:
+        if len(remaining) <= max_chars:
+            parts.append(remaining)
+            break
+        cut = remaining.rfind(". ", 200, max_chars)
+        if cut == -1:
+            cut = remaining.rfind(" ", 300, max_chars)
+        if cut == -1:
+            cut = max_chars
+        parts.append(remaining[:cut+1])
+        remaining = remaining[cut+1:].lstrip()
+    return parts
+
+# === Main generation ===
+def generate(input_path, output_dir):
+    input_path = Path(input_path)
+    output_dir = Path(output_dir)
+    output_dir.mkdir(parents=True, exist_ok=True)
+    
+    name = input_path.stem
+    
+    print(f"Loading Silero TTS v5 (voice: {SPEAKER})...")
+    model = load_model()
+    
+    text = input_path.read_text(encoding="utf-8")
+    segments = parse_segments(text)
+    
+    print(f"Found {len(segments)} segments:")
+    robot_count = sum(1 for t, _ in segments if t == "robot")
+    print(f"  Normal: {len(segments) - robot_count}, Robot: {robot_count}")
+    
+    all_audio = []
+    demo_audio = []
+    demo_count = 0
+    
+    for i, (stype, stext) in enumerate(segments):
+        print(f"  [{i+1}/{len(segments)}] {stype:6s} {stext[:50]}...")
+        
+        parts = split_long(stext)
+        segment_audio = []
+        for part in parts:
+            stressed = apply_stress(part) if USE_STRESS else part
+            audio = model.apply_tts(text=stressed, speaker=SPEAKER, sample_rate=SAMPLE_RATE)
+            audio_np = audio.cpu().numpy() if isinstance(audio, torch.Tensor) else np.array(audio)
+            segment_audio.append(audio_np)
+        
+        combined = np.concatenate(segment_audio)
+        
+        if stype == "robot":
+            try:
+                import librosa
+                combined = make_robotic(combined, SAMPLE_RATE)
+            except ImportError:
+                pass
+        
+        pause = np.zeros(int(SAMPLE_RATE * 0.3))
+        all_audio.append(combined)
+        all_audio.append(pause)
+        
+        if demo_count < 4:
+            demo_audio.append(combined)
+            demo_audio.append(np.zeros(int(SAMPLE_RATE * 0.3)))
+            demo_count += 1
+    
+    # Save full
+    final = np.concatenate(all_audio)
+    final = final / np.max(np.abs(final)) * 0.9
+    full_path = output_dir / f"{name}_full.wav"
+    sf.write(str(full_path), final, SAMPLE_RATE)
+    dur = len(final) / SAMPLE_RATE
+    print(f"\n✅ {full_path} ({dur:.0f}s = {dur/60:.1f}min)")
+    
+    # Save demo
+    demo = np.concatenate(demo_audio)
+    demo = demo / np.max(np.abs(demo)) * 0.9
+    demo_path = output_dir / f"{name}_demo.wav"
+    sf.write(str(demo_path), demo, SAMPLE_RATE)
+    demo_dur = len(demo) / SAMPLE_RATE
+    print(f"✅ {demo_path} ({demo_dur:.0f}s demo)")
+
+if __name__ == "__main__":
+    if len(sys.argv) > 1:
+        input_file = sys.argv[1]
+    else:
+        input_file = "Silas.md"
+    
+    generate(input_file, "tts/output")