CycleAcoustics - Blender Reverb IR Generator Add-on

CycleAcoustics: Model Rooms 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.

Start with one of the starter template .blend files. You need the CycleAcoustics materials and a specific render setup for it to work. Render it with a mirror ball camera and then generate the 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).

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

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.

Psychoacoustic Processing

Basic Mode: Reverb reflections get panned left and right depending on the direction from which they hit the listener. 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.

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).
• 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).

Resources

F.A.Q

Why did Blender stop responding after I clicked the "Generate Impulse Response" button?

This is normal behavior. The algorithm may take seconds to minutes to build an impulse response depending on the render resolution and the number of reflections in the rendered scene. To speed up IR generation, try rendering at a smaller resolution.

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).

Version History

Release Notes:

11 Aug 2024 - 1.2.0 - Added an option to exclude direct sound from IR outputs in order to get "wet only" IRs for use in music production with dry/wet mixing. Patched a bug that makes polarity incorrect. Compositing change: made the alpha values of "empty" pixels 1 (from 0.5 in the previous version); this change makes no difference to audio output and just improves rendered images’ visual clarity to users.

6 Aug 2024 - 1.1.0 - More accurate binaural processing. Calculation for direction-based time difference between left and right ears is more accurate. Improved high-frequency sound reproduction for reflections at fractional-sample delays by using sinc interpolation. The sound emitter material now correctly accounts for travel times from emitters to first bounces.

2 Aug 2024 - 1.0.0 - Initial Release