# How We Hear in 3D: The Science of Spatial Sound

> Learn how we hear in 3D: time and level differences between the ears, HRTF and pinna cues, distance, and why binaural headphones can recreate spatial sound.

Web page: https://spatial9.ai/blog/academy-how-we-hear-in-3d
Author: Spatial9 Team
Published: 2026-10-04. Updated: 2026-10-04.

## Key takeaways
- The brain separates left from right using interaural time difference (ITD) for low frequencies and interaural level difference (ILD) for high frequencies.
- For a human head, the largest possible interaural time difference is less than one millisecond, yet the auditory system resolves much smaller differences.
- In open space a sound gets about 6 dB quieter each time the distance doubles, and the direct-to-reverberant ratio is one of the strongest indoor distance cues.
- A small head turn resolves front-back ambiguity on the cone of confusion, which is why head tracking makes binaural headphone audio more convincing.

In this lesson: You will learn how two ears and one brain turn pressure waves into a full 3D map of the world around you. We cover time and level differences, the filtering of your outer ear, distance cues, and the precedence effect. Then you will hear every one of those cues at work in the Immersive Classroom.

Close your eyes for a moment. You can still tell where the door is when someone opens it. You know the car is behind you and to the left. You can hear that the rain is above you, on the roof, and not in front of you on the floor.

You do all of this with just two small openings on the sides of your head. No cameras, no sensors, no extra hardware. Your brain reads tiny differences between your two ears and builds a 3D world from them, every waking second.

Every immersive mix you will ever make, for music, film, games or virtual reality, works because of this machinery. When you understand how people hear in 3D, you stop guessing about spatial audio. You start designing for the brain that will actually listen to your work.

This is the first lesson of Spatial9 Academy, and it is the foundation for everything that follows.


## What you will learn

- How interaural time difference (ITD) and interaural level difference (ILD) tell you left from right.
- Why the shape of your outer ear gives each direction its own tonal fingerprint, called the HRTF.
- What the cone of confusion is, and how a small turn of the head solves it.
- How you judge elevation and distance, and why the first sound to arrive wins.
- Why headphones and binaural rendering can place sound all around you.

The rest of this lesson is free with a Spatial9 account: https://spatial9.ai/blog/academy-how-we-hear-in-3d