scripts/generate_drums.py

"""Generate one-shot drum samples using DSP synthesis.

Creates WAV files for: kick, snare, hihat, crash, ride, tom_high, tom_low.
Uses scipy filters for realistic frequency shaping and layered synthesis.
"""

import numpy as np
from scipy.io import wavfile
from scipy.signal import butter, lfilter
from pathlib import Path

SR = 44100
OUT_DIR = Path(__file__).parent.parent / "app" / "public" / "drums"

np.random.seed(42)


def _normalize(signal, peak=0.85):
    mx = np.max(np.abs(signal))
    if mx > 0:
        signal = signal * (peak / mx)
    return signal.astype(np.float32)


def _highpass(signal, freq, sr=SR, order=4):
    nyq = 0.5 * sr
    b, a = butter(order, freq / nyq, btype='high')
    return lfilter(b, a, signal)


def _lowpass(signal, freq, sr=SR, order=4):
    nyq = 0.5 * sr
    b, a = butter(order, freq / nyq, btype='low')
    return lfilter(b, a, signal)


def _bandpass(signal, low, high, sr=SR, order=4):
    nyq = 0.5 * sr
    b, a = butter(order, [low / nyq, high / nyq], btype='band')
    return lfilter(b, a, signal)


def make_kick():
    dur = 0.45
    n = int(SR * dur)
    t = np.linspace(0, dur, n, endpoint=False)

    # Pitch sweep: 150Hz -> 45Hz with exponential decay
    freq = 45 + 105 * np.exp(-t * 25)
    phase = 2 * np.pi * np.cumsum(freq) / SR
    body = np.sin(phase)

    # Amplitude envelope: punchy attack, moderate decay
    env = np.exp(-t * 7) * (1 - np.exp(-t * 500))

    # Sub-bass thump (separate low sine for weight)
    sub = np.sin(2 * np.pi * 50 * t) * np.exp(-t * 12) * 0.4

    # Transient click
    click_n = int(SR * 0.004)
    click = np.random.randn(click_n) * 0.25
    click *= np.linspace(1, 0, click_n)

    signal = body * env + sub
    signal[:click_n] += click

    # Lowpass to remove harmonics above 200Hz
    signal = _lowpass(signal, 200)

    return _normalize(signal)


def make_snare():
    dur = 0.3
    n = int(SR * dur)
    t = np.linspace(0, dur, n, endpoint=False)

    # Body: sine at 185Hz with fast decay
    body = np.sin(2 * np.pi * 185 * t) * np.exp(-t * 18) * 0.6

    # Second harmonic for richness
    body2 = np.sin(2 * np.pi * 330 * t) * np.exp(-t * 25) * 0.2

    # Snare wires: bandpassed noise (1kHz-9kHz)
    noise = np.random.randn(n)
    wires = _bandpass(noise, 1000, 9000)
    wire_env = np.exp(-t * 12)
    wires = wires * wire_env * 0.5

    # Sharp transient
    click_n = int(SR * 0.002)
    click = np.random.randn(click_n) * 0.5
    click *= np.linspace(1, 0, click_n)

    signal = body + body2 + wires
    signal[:click_n] += click

    return _normalize(signal)


def make_hihat():
    dur = 0.08
    n = int(SR * dur)
    t = np.linspace(0, dur, n, endpoint=False)

    # High-frequency noise
    noise = np.random.randn(n)
    signal = _highpass(noise, 6000)

    # Very tight envelope
    env = np.exp(-t * 60) * (1 - np.exp(-t * 2000))
    signal = signal * env

    return _normalize(signal, peak=0.7)


def make_crash():
    dur = 1.5
    n = int(SR * dur)
    t = np.linspace(0, dur, n, endpoint=False)

    # Broadband noise with emphasis on 3-8kHz
    noise = np.random.randn(n)
    bright = _bandpass(noise, 3000, 12000) * 0.7
    body = _bandpass(noise, 800, 4000) * 0.3

    signal = bright + body

    # Long decay envelope with sharp attack
    env = np.exp(-t * 2.5) * (1 - np.exp(-t * 1000))
    signal = signal * env

    return _normalize(signal, peak=0.7)


def make_ride():
    dur = 0.6
    n = int(SR * dur)
    t = np.linspace(0, dur, n, endpoint=False)

    # Tighter noise than crash, more "ping" character
    noise = np.random.randn(n)
    bright = _highpass(noise, 5000) * 0.6

    # Add a subtle metallic tone (inharmonic mix of sines)
    ping = (np.sin(2 * np.pi * 4200 * t) * 0.15 +
            np.sin(2 * np.pi * 5800 * t) * 0.10 +
            np.sin(2 * np.pi * 7100 * t) * 0.08)

    signal = bright + ping

    # Medium decay
    env = np.exp(-t * 4) * (1 - np.exp(-t * 1500))
    signal = signal * env

    return _normalize(signal, peak=0.6)


def make_tom(freq_base=120, dur=0.35):
    n = int(SR * dur)
    t = np.linspace(0, dur, n, endpoint=False)

    # Pitched membrane: frequency sweep down
    freq = freq_base * 0.6 + freq_base * 0.4 * np.exp(-t * 15)
    phase = 2 * np.pi * np.cumsum(freq) / SR
    body = np.sin(phase)

    # Amplitude envelope
    env = np.exp(-t * 8) * (1 - np.exp(-t * 800))

    # Slight noise for attack character
    click_n = int(SR * 0.005)
    click = np.random.randn(click_n) * 0.2
    click *= np.linspace(1, 0, click_n)

    signal = body * env
    signal[:click_n] += click

    # Bandpass around the fundamental
    signal = _bandpass(signal, freq_base * 0.4, freq_base * 3)

    return _normalize(signal, peak=0.8)


def write_wav(name, data):
    path = OUT_DIR / f"{name}.wav"
    # Convert float32 [-1, 1] to int16
    int_data = (data * 32767).astype(np.int16)
    wavfile.write(str(path), SR, int_data)
    size_kb = path.stat().st_size / 1024
    print(f"  {name}.wav: {len(data)/SR:.3f}s, {size_kb:.1f}KB")


if __name__ == "__main__":
    OUT_DIR.mkdir(parents=True, exist_ok=True)
    print("Generating drum samples...")

    write_wav("kick", make_kick())
    write_wav("snare", make_snare())
    write_wav("hihat", make_hihat())
    write_wav("crash", make_crash())
    write_wav("ride", make_ride())
    write_wav("tom_high", make_tom(freq_base=200, dur=0.25))
    write_wav("tom_low", make_tom(freq_base=100, dur=0.4))

    print("Done!")