How I Built a Sleep Audio Factory That Earns $10+ RPM While I Sleep (NumPy + ffmpeg + Voxtral)

NumPy synthesis → ffmpeg encoding → Voxtral TTS narration → 10-hour loop

def generate_brown_noise(duration_sec: float, amplitude: float = 0.3) -> np.ndarray:
    samples = int(duration_sec * 44100)
    white = np.random.randn(samples)
    brown = np.cumsum(white)
    brown = brown / np.max(np.abs(brown)) * amplitude
    return brown.astype(np.float32)

def generate_binaural(duration_sec: float, base_hz: float = 200, beat_hz: float = 2.0):
    t = np.linspace(0, duration_sec, int(duration_sec * 44100))
    left  = np.sin(2 * np.pi * base_hz * t) * 0.3
    right = np.sin(2 * np.pi * (base_hz + beat_hz) * t) * 0.3
    return np.stack([left, right], axis=1).astype(np.float32)

RECIPES = {
    "ocean-theta": {
        "layers": [
            {"type": "binaural", "freq": 6.0, "amplitude": 0.15},   # theta
            {"type": "brown",    "amplitude": 0.20},                 # ocean body
            {"type": "pink",     "amplitude": 0.08},                 # surf texture
        ]
    },
    "rain-delta": {
        "layers": [
            {"type": "binaural", "freq": 2.0, "amplitude": 0.12},   # delta
            {"type": "brown",    "amplitude": 0.25},
            {"type": "white",    "amplitude": 0.06},                 # rain hiss
        ]
    },
}

# Step 1: 1-hour base
python3 generate_sleep_audio.py --type mix --recipe ocean-theta --duration 3600 --out base.mp3

# Step 2: 10-hour loop (runs in seconds, not hours)
ffmpeg -stream_loop 9 -i base.mp3 -c copy sleep-ocean-10hr.mp3

def tts_segment(text: str, voice: str = "paul") -> bytes:
    payload = {
        "model": "voxtral-mini-tts-2603",
        "input": text,
        "voice": "en_paul_sad",        # subdued, calm — works for sleep
        "response_format": "mp3",
    }
    resp = requests.post(
        "https://api.mistral.ai/v1/audio/speech",
        headers={"Authorization": f"Bearer {MISTRAL_API_KEY}"},
        json=payload,
        timeout=60,
    )
    body = resp.json()
    return base64.b64decode(body["audio_data"])

Welcome to Deep Sleep Sounds.

[pause 5s]

Tonight, a story called Adrift on a Calm Sea.

[pause 5s]

Find the position your body most wants to be in.

ffmpeg -i narration.mp3 -i ocean-theta-1hr.mp3 \
  -filter_complex "[0:a]volume=1.0[narr];[1:a]volume=0.35[bed];[narr][bed]amix=inputs=2:duration=longest[out]" \
  -map "[out]" -c:a libmp3lame -q:a 2 final.mp3

audio_path = Path(f"out/{audio_name}")
if not audio_path.exists() or audio_path.stat().st_size < 10_000:
    print("❌ Audio file missing or too small — aborting")
    sys.exit(1)

for attempt in range(5):
    try:
        return tts_segment(text, voice)
    except RateLimitError:
        time.sleep(2 ** attempt + random.random())

mix = mix / np.max(np.abs(mix)) * 0.95  # leave 5% headroom