Binaural 3D Mixing

By David Poirier-Quinot & Jean-Marc Lyzwa

Binaural 3D mixing has several specificities compared to traditional stereo mixing. First, it offers a realistic, immersive, and outside-the-head sound image, which is quite different from the inside-the-head image of stereo listening with headphones. It also allows the artificial recreation of a natural sound perception. To succeed, it relies on simulating how sound is affected by the listener’s external ears, using what is called the “Head Related Transfer Function” or HRTF. These HRTFs are unique to every person, like an acoustic fingerprint, representing what the brain uses to locate where sounds are coming from.

Binaural mixing uses a rendering engine with a single HRTF chosen from scientific studies. Since the HRTF is unique to each person, this means the sound engineer is mixing with someone else’s ears for other people’s ears.

In creating a full 360° spherical sound field, rather than the limited frontal 60° of stereo, this 3D mixing for a chosen listening position allows the engineer to precisely construct a sound image of a given scenography while limiting the risk of different sounds masking each other. This project was built progressively by successively adding the different sonic layers.

Although some reduction in quality can be expected due to differences in listeners’ HRTFs and headphones, the result should satisfy most people. The challenge is to achieve a mix which is both a technical and artistic creation, in which everyone perceives all the subtleties.