Houdini Audio Reactive Rig

Houdini Audio Reactive Rig (CHOP-less)

A lightweight, drop-in audio→motion rig for Houdini that doesn’t rely on CHOPs. It analyzes a WAV file inside a single Python SOP and outputs one point per frequency band with a clean @amp attribute you can use to drive anything—scale, color, instancing, shaders, camera… you name it.

What it does

- Per-band analysis using the Goertzel algorithm (fast, FFT-free).

- Log-spaced bands from Freq Min → Freq Max (musically natural).

- Attack/Release envelopes per band for musical smoothing.

- Optional normalization to keep values in a friendly 0–1 range.

- Live preview: a ready-made sphere visualization driven by @amp.

- Robust on “lean” Houdini builds: no analyze, no amp, no CHOP networks required.

Parameters

- Audio File: 16-bit PCM .wav (mono or stereo; stereo auto-mixes to mono).

- Bands: number of frequency bands (e.g., 8, 16, 24, 32).

- Freq Min / Freq Max: analysis range (e.g., 40 → 12000 Hz).

- Win Size / Hop: analysis window & hop in samples (defaults work well; lower for snappier, higher for smoother).

- Attack / Release: per-band envelope times (seconds).

- Gain: pre-visual scaling before normalization.

- Normalize 0..1: auto-scales envelopes to a stable unit range.

- (Hidden) Cook Ticker: forces time-dependent updates every frame.

Output

The Python SOP creates a single point per band with:

- f@amp — normalized amplitude (0..1)

- f@freq — the center frequency of the band (Hz)

Download...