CycleAcoustics: Model Rooms (and Caves, Halls, etc.) and Hear How They Sound Inside!

CycleAcoustics is a Blender add-on for generating reverb impulse responses from models of reverberant environments, such as rooms—a sound design tool for Blender artists, music producers, filmmakers, and more. As a portmanteau of "Cycles" and "psychoacoustics", it simulates sound using Cycles raytracing to generate convolution reverb impulse responses, and the add-on’s full edition supports psychoacoustic processing.

Video

CycleAcoustics uses the Cycles render engine to trace paths that sound can take from an emitter object to a listener or microphone (represented by the camera). It uses special material setups that keep track of total ray travel distances, number of bounces, and high and low frequencies.

By generating reverb impulse responses from 360º-degree camera renders, the IR generation algorithm pans and alters the timing and frequency responses of incoming sound “rays” based on their angular directions.

Usage Notes

• For the calculations to work as intended, the Cycles sample count must be set to 1. Don’t raise the sample count to increase quality; to get more lush reverb, enlarge the render resolution (make sure it’s square).
• Larger resolutions “catch” more reflections and thus allow for more lush-sounding reverb, but there always comes a point where more pixels is overkill because it basically sounds the same. Smaller resolutions can still produce good-sounding reverbs, depending on the size of your scene (bigger rooms generally need higher resolutions for more reflections to fill out their longer reverb tails).
  
• To save a CycleAcoustics render for later IR generation, you can save the render result as an EXR file. The format should be 32-bit RGBA (not RGB).

Begin with one of the starter template .blend files. You need the CycleAcoustics materials and a specific render setup for it to work; the template files have them all set up and ready to use. Render with a 360º mirror ball camera and then generate a stereo impulse response.

Set the scale of your scene with the speed of sound in Blender units per second. 44.1 KHz and 48 KHz audio sample rates are supported. The full edition has a psychoacoustic mode and the option to exclude direct sound (to generate "wet only" IRs).

Template Scenes

Impulse responses generated by CycleAcoustics imported into Audacity (free audio editing software) and downmixed to mono:

Psychoacoustic Processing

Basic Mode: Provides basic reverb processing where reflections are panned left and right depending on their direction, with no changes to frequency response.

Psychoacoustic Mode (Full Edition Only): Reverb reflections get slightly delayed in the left and right channels depending on the direction from which they hit the listener. For example, a sound that comes from in front of the listener arrives at both of the listener’s ears at the same time, and a sound that comes from the left side of the listener arrives at their left ear before it arrives at their right ear. Direction also affects frequency response—the head, body, and ears cause frequencies in incoming sounds to be attenuated and boosted.

Feature Set Comparison

Lite Edition: Includes the add-on with basic mode and 1 environment (Living Room & Kitchen).

Full Edition: Includes the add-on with psychoacoustic mode, indirect-only mode, and 4 environments (Living Room & Kitchen, Bathroom, Gymnasium, and Tunnel).

The Lite edition only comes with 1 room environment and does not have the psychoacoustic processing option. The full edition has a setting to generate "wet only" impulse responses intended for use in music production applications with dry/wet mixing.

What this add-on does:

• Make stereo reverb impulse responses from scenes that use CycleAcoustics materials
• Timing is based on the speed of sound (you can change it) so scenes modeled to scale have accurate sound travel times
• Psychoacoustic audio processing (in full version only)

What this add-on does not do:

• Realtime dynamic reverb
• Simulate reverb on non-CycleAcoustics materials
• Physically realistic wave interference and diffraction