When you close your eyes and hear a sound, say, a door slamming behind you or birds beeping outside a window, your brain instantly determines where it’s coming from and what kind of space you’re in. That inherent sense of space isn’t created by the sound itself; it is created by the combination of the sound with the space and your ears. This is where Binaural Room Impulse Responses (BRIRs) come in.
At Brandenburg Labs, BRIRs play a key role in how we simulate real loudspeaker setups over headphones. In this blog, we’ll take a closer look at what BRIRs are, why they matter, and how they help us to create lifelike, immersive virtual audio spaces.
What is BRIR?
A Binaural Room Impulse Response captures how a specific room and loudspeaker setup affects the sound reaching a listener’s ears. In simpler terms, it’s a recording of how sound travels from a loudspeaker to each of your ears, including all reflections, reverberations, and filters applied by your head, torso, and pinnae (outer ears).
Imagine clapping your hands in a concert hall. The echo you hear isn’t just a sound bouncing off walls, it’s a complex mixture of early reflections, reverberation tails, and the way your body receives and processes them, a BRIR captures all that data. Mathematically, a BRIR is a convolution of a Head-Related Transfer Function (HRTF) and a RIR, meaning it takes into consideration both your physical auditory anatomy and the environment around you.
BRIR vs. HRTF: What’s the Difference?
You might remember from our previous blog about Binaural audio that a HRTF lets you hear where a sound is coming from, but not what kind of room it’s in.
A BRIR, by contrast, is a Room Impulse Response (RIR) for instance measured at the ear of a listener, meaning it incorporates the HRTF along with the acoustic characteristics of the room. That includes reflections from walls, floor, ceiling, and objects, distance and placement of the loudspeaker, reverberation and decay time, and lastly, listener position and orientation. Think of HRTFs as describing directional hearing, while BRIRs encode spatial presence.
How Are BRIRs Measured?
Recording a BRIR typically involves placing a dummy head, or sometimes a real person, equipped with binaural microphones, in a fixed position within a room. A known test signal, such as a swept sine wave or a sharp impulse, is then played from a loudspeaker positioned at a specific location. As the sound travels through the space, it interacts with the room’s surfaces and the listener’s anatomy, including the head, torso, and outer ears. The resulting sound is recorded separately at both ears, producing two distinct impulse responses, one for the left ear and one for the right. These recordings encapsulate all the spatial and acoustic information needed to recreate the same auditory experience over headphones.
At Brandenburg Labs, our Deep Dive Audio system uses BRIRs to recreate a virtual loudspeaker setup over headphones. When setting up our demo for worldwide exhibitions, we start by capturing acoustic measurements using an omnidirectional microphone. To do this, we play a sine sweep over the loudspeaker(s), which is then recorded by the microphone, in order to acquire the room impulse response containing the reflections of the room we are in. This room impulse response is then used by our algorithm. The measured RIR is merged using the described convolution with a generic HRTF recorded without room information to obtain the desired BRIR. The entire process only takes a few minutes and is done for each room in which we are setting up the demo.
If you would like to explore more on how our technology demo works, please visit our Frequently asked questions section on our ‘Contact’ page.
