What is HRTF: listening to positional sound in games

Of course, you use it or have used it, but you don’t know what it’s called or what it does. This HRTF Technology in English is called “Head Related Transfer Function” or “Head Related Transfer Function” and it is what allows us to have positional audio in games , Do you want to know what it is and how it works? Here we explain it to you.

Not all people perceive sound in the same way, and not because of the level of hearing that we can have, but also because of the shape and size of our heads and ears, ears. For this reason, HRTF technology exists, but before we go on to explain what it is and how it works, we must first explain some previous concepts.


Hearing in humans.
Humans can determine the origin of sounds in the three spatial dimensions that we all know. Likewise, we can weigh the distance at which a sound is located by the brain, inner ear, and outer ears working together.

The auditory cortex receives signals from each of the ears separately in monophonic signals sending them to the association cortex where they are compared, resulting in information in the form of a binaural signal that combines the difference in arrival time and the difference in intensity. These monophonic signals come from the interaction between the sound source and the human anatomy , in which the source sound is modified before it reaches the ear canal for processing.

These modifications encode the location of the source and can be captured by the impulse response, which relates the location of the sound source to the location of the ear relative to it. This impulse response is called the Head Impulse Response ( HRIR ) and the convolution (which is a mathematical operator that converts two functions into a third representing the magnitude they impose) of an arbitrary source sound using HRIR converts the sound the listener would hear if it were played at the source location to the listener’s ear and the receiver location.

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What is HRTF?

It is what we know as virtual surround sound , It is a function that characterizes how the ear receives sound from a point in space. When sound is exposed to the listener, the density of the head as well as the size and shape of the earmolds change the sound and affect its perception by increasing some frequencies and attenuating others.

HRTF sound variation

Generally speaking, the HRTF increases frequencies from 2 to 5 kHz with a primary resonance of +17 dB to 2,700 Hz, although the response curve varies considerably from person to person.

The HRTF is currently used for both ears, synthesizing a binaural sound that seems to emanate from a specific point in space (XYZ). Hence, a transfer function that describes how sound from a certain point will reach the ear .

How does this technology work?

The associated mechanism varies between people because, as we have explained, each person has a different head and ear shape. However, this technology attempts to emulate the average for a human to provide the most accurate positional audio possible.

HRTF describes how a given sound wave input, which has been parameterized as frequency and source location, is pre-filtered (obviously by the game’s sound designers) by the diffraction and reflection properties of the head, auricle and torso before the sound reaches the transduction. The mechanism of the eardrum and inner ear.

This seems complicated, but in a nutshell it simply means that it is a technology that allows sound engineers to parameterize sound to tell us in what position we should listen to each sound. There is a transfer function in between, yes, but that is the topic of these audio engineers and what we need to understand is what determines the location of the sound in virtual space .


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