Spatial Audio Resources

Reference assets for ambisonic binaural monitoring: HRIR filters suited to immersive 360/VR playback and related decoders. Use these when building preview tools or monitoring ambisonic mixes in a DAW.

These are listening/monitoring assets, not metadata injection code. To tag MP4/MOV files with spatial audio metadata (SA3D atoms), use the browser demo, the CLI/GUI (-a), or the Docker web UI. See the Spatial Audio RFC for the box format.

Get the files

HRIR WAV files are in the repository under audio/ and packaged as audio.zip on GitHub Releases. Clone the repo or download the zip.

Directory overview

Raw symmetric cube HRIRs

Binaural measurements (Head Related Impulse Responses) from a cube loudspeaker configuration, used in a first-order ambisonic binaural decoder. Derived from the SADIE binaural measurements as individual time-domain FIR filters.

Specification

An ambiX binaural decoder preset (cube.config) is included.

Note: Using these filters directly (or via the ambiX preset) will not match every reference decoder output unless you also apply phase-matched shelf filters, as described in Is My Decoder Ambisonic? (Heller, Lee, Benjamin). For a closer match without custom shelf design, use the symmetric ambisonic binaural decoder set below.

Symmetric ambisonic binaural decoder

Spherical harmonic HRIR filters for first-order ambisonic binaural decode. Apply them to an ambisonic mix and route the convolver outputs to stereo L/R:

Convolution (*) can be done with multichannel convolver plugins such as LAConvolver (macOS) or Freeverb3 (Windows). The dotted red line with Ø denotes 180° phase inversion.

Ambisonic correction filters

Filters that compensate for HRTF changes when switching the binaural decoder from THRIVE to SADIE KU100. Apply them to ambiX tracks so existing mixes retain similar timbre after the decoder change.

Before correction: spectral shift when switching decoders:

After correction: minimized difference:

Signal flow when applying correction in the DAW:

FAQs

Why did you change HRTFs?

Binaural decoding depends on HRTFs, which vary by listener. In listening tests (53 participants, mobile VR, varied content), the SADIE KU100 set ranked highest on average when individualized HRTFs were unavailable:

Should I monitor with HRTFs when mixing for 360/VR?

Yes. Use the symmetric ambisonic binaural decoder filters and/or preview on your target platform to judge timbre and loudness. Decoder choice affects both coloration and level.

What is timbral coloration?

HRTFs impose listener-specific spectral coloration. Example frequency responses for THRIVE vs SADIE KU100:

Can I retune an existing THRIVE-monitored mix?

Apply the correction filters to your ambiX tracks to align timbre with the SADIE KU100 decoder.

Expected loudness

Binaural decode level depends on the HRTF set. The reference decoder targets loudness comparable to a standard M/S stereo decoder. Example measurements (0.5 normalized pink noise, eight directions, ITU-R BS.1770-4):

Peaks may exceed 0 dBFS even when integrated loudness matches.

Third-party monitoring tools

Plugins such as BlueRippleSound O3A View, Noisemakers AmbiHead, and SoundParticles implement binaural preview using these HRIR sets, aligned with common 360/VR playback.