Sound-Reactive Particle Field (Synthetic Audio)

Math essence

audio(t) = Σ amp_i * sin(2π freq_i t + phase_i). Field_x = field_strength * audio + beat_gain * d(audio)/dt, Field_y = slow baseline oscillator. Velocity update with max_speed clamp. Canvas *= trail_decay, then add ink * 0.10 at each particle position. Hue rotates by hue_shift per step.

Parameters

Reference

First 60 lines of reference.py. Full source: library_external/toxi_openframeworks/SoundReactiveField/reference.py

from __future__ import annotations

from typing import ClassVar

import numpy as np


class SoundReactiveField:
    """Sound-reactive particle field driven by a synthetic audio chain.

    A bank of N sinusoids acts as the "audio signal":

        audio(t) = Σ_i  amp_i * sin(2π freq_i t + phase_i)

    The instantaneous magnitude of this sum (and its derivative,
    treated as a beat-onset detector) drives a horizontal force field
    across the canvas. Particles feel this field, drift in the
    direction of the force, and leave a low-alpha trail on a fading
    canvas — the iconic look of openFrameworks audio-reactive
    visuals (Nick Hardeman, Anthony Scavarelli, and the `oF` chapter
    in the ofBook's *Sound* section all use this same skeleton).
    """

    family: ClassVar[str] = "toxi_openframeworks"
    sketch: ClassVar[str] = "soundreactivefield"

    def __init__(
        self,
        dim: int = 400,
        num_particles: int = 1200,
        num_bands: int = 5,
        band_freqs: tuple[float, ...] = (0.42, 0.97, 1.7, 2.5, 3.3),
        band_amps: tuple[float, ...] = (0.6, 0.45, 0.35, 0.25, 0.2),
        field_strength: float = 2.4,
        beat_gain: float = 4.0,
        max_speed: float = 4.5,
        trail_decay: float = 0.965,
        hue_shift: float = 0.012,
        bg_color: tuple[int, int, int] = (8, 10, 18),
        seed: int | None = None,
    ) -> None:
        self.dim = dim
        self.num_particles = num_particles
        self.num_bands = num_bands
        self.band_freqs = np.array(band_freqs, dtype=np.float32)
        self.band_amps = np.array(band_amps, dtype=np.float32)
        self.field_strength = field_strength
        self.beat_gain = beat_gain
        self.max_speed = max_speed
        self.trail_decay = trail_decay
        self.hue_shift = hue_shift
        self.bg_color = np.array(bg_color, dtype=np.float32)
        self._seed = seed
        self._t = 0.0
        self._last_audio = 0.0
        self._hue = self.rng.integers(0, 360) if False else 0
        self.reset()

    def reset(self, seed: int | None = None) -> None:
        if seed is not None: