why

your HRTF is personal

What is the problem?

If your ordinary headphones can produce 3D audio, then why is 3D audio not as common as 3D vision? Because it needs extensive personalization to work well. For 3D vision this is not necessary: the distance between both eyes is similar for everyone, so the same pair of goggles, with small interpupillary adjustments, will work for everyone. However, for 3D audio such a one-size-fits-all solution does not work.  Everyone’s head and ear shapes are really different, so their interactions with sounds are really different as well (i.e. HRTFs are really personal). Consequently, everyone hears the world differently and this spoils the 3D audio experience dramatically: sounds that should arrive from the front appear from the back, etc. Often, the 3D effect disappears altogether and all sounds seem to come from inside instead of outside the listener's head. Therefore, to experience real 3D audio it is necessary to account for your unique head and ear shape by means of a personal HRTF.

 

Ondertitel

3D audio is key to a truly immersive experience. But as we all hear the world differently due to the unique shape of our ears and head, true immersion is difficult to achieve. Earfish now provides a low-cost solution to tailor your 3D audio experience to your uniqueness. You can apply Earfish’s solution at home. All you need is your smartphone (with a stereo-recording module), two in-ear microphones and a speaker.

what

3D audio through headphones

What is 3D audio?

3D audio is conceptually similar to 3D vision. You might not have realized:  you not only see, you also hear the world in 3D! You don’t just hear plain stereo, you obtain a spatial sense of your surroundings: you discern sounds coming from above from those coming from below, those behind you from those located in front, those far away from those close by. If you think about it, it is actually quite amazing that you can do this with only two ears. And, just like stereo goggles can make you see the world in 3D, stereo headphones can trick your brain into experiencing a 3D soundscape. Say hello to 3D audio.

what2

revolving noise source
(listen with headphones)

How does it work?

3D vision relies on the fact that both eyes ‘see’ the world differently because they are a certain distance apart. This is why you have to wear stereo goggles, to present the left and right eye with slightly different images. From these differences your brain then constructs a 3D view of the world.  Similarly, you hear the world in 3D because each ear experiences the world differently. Not only are they a distance apart and on opposite sides of your head, but the shape of your ears results in specific interactions with the incoming sound waves. As a result, depending on where the sound is coming from, it sounds different. The way the ears interact with sounds from a 3D world can be stored in a file: the so-called HRTF (head-related transfer function). Using this file, we can present, through stereo headphones, the left and right ear with slightly different sounds that are interpreted by your brain as originating from a real 3D world.

 

why

your HRTF is personal

What is the problem?

If your ordinary headphones can produce 3D audio, then why is 3D audio not as common as 3D vision? Because it needs extensive personalization to work well. For 3D vision this is not necessary: the distance between both eyes is similar for everyone, so the same pair of goggles, with small interpupillary adjustments, will work for everyone. However, for 3D audio such a one-size-fits-all solution does not work.  Everyone’s head and ear shapes are really different, so their interactions with sounds are really different as well (i.e. HRTFs are really personal). Consequently, everyone hears the world differently and this spoils the 3D audio experience dramatically: sounds that should arrive from the front appear from the back, etc. Often, the 3D effect disappears altogether and all sounds seem to come from inside instead of outside the listener's head. Therefore, to experience real 3D audio it is necessary to account for your unique head and ear shape by means of a personal HRTF.

 

why2


HRTF measurement at
RWTH Aachen University

How to obtain your personal HRTF?

Ideally, your HRTF is measured in a specialized facility under controlled conditions. During such a measurement, a sound is played through a loudspeaker from a certain direction and microphones placed at the entrance of your ear canal register how your ears 'hear' this sound. This is repeated for all directions covering the sphere surrounding you. While the measurement procedure is conceptually simple, it requires sophisticated and expensive infrastructure to execute properly, which you are unlikely to have at home.

For the past ten years, different research teams have been searching for an easy way to obtain an HRTF at home. Since an acoustical measurement was not deemed possible, a common strategy was (and still is) to focus on the characterization of the shape of your head and/or ears. After all, it is their shape that determines the HRTF and they are more tangible than the invisible HRTF. And so the problem was shifted to finding ways to characterize the shape in sufficient detail with the limited facilities at home. With our technology we show that this detour is not necessary and that it is fairly easy to actually measure your HRTF at home in a way similar to that used in a specialized facility. And as Lord Kelvin already knew: to measure is to know.

 

How

How do we do it?

The basic idea is very simple. Whereas in a typical HRTF measurement your head is fixed and the loudspeaker position changes, sampling the sphere around your head during the measurement, this is reversed in our setup. Here, you are seated in front of one of your loudspeakers at home and, while a sound file provided by us is playing, you rotate your head freely in all possible directions. From the viewpoint of your head, the sound is always coming from a different direction as you move your head, again providing a sampling of the sphere around your head. The measurement can be performed with different setups (see below), but in the hardcore DIY method your smartphone is fixed to your head and collects all the data. After about 15 minutes of moving your head around, the collected data is uploaded to Earfish where your personal HRTF is calculated by our proprietary algorithms (patent pending).  Finally, we send you your HRTF file in SOFA format, ready to be used.

 

 

how2

standard measurement vs Earfish measurement

how3

data collected during Earfish measurement

how4

Can you do it yourself?

Yes! We are currently working on a commercial product that should make it really easy for you to measure your HRTF at home. But until then we are happy to share our technology with you for free if you are willing to help us improve it further. We will soon post two videos in which we demonstrate step by step how you can measure your HRTF at home. It only requires a few (commercially available) components and some handiness from your side. For the timing being, we will do the HRTF calculations for free.

The first setup (DIY setup 1) uses a smartphone and additional hardware costing about 50 Euro. Mounted on your head, the smartphone tracks your head movements, while simultaneously recording the audio delivered by in-ear microphones.

 

how5

DIY setup 2

Of course the smartphone will interfere somewhat with the interactions of the sound waves with your head and ears and hence alter your HRTF a bit. As a result, using this HRTF the world will sound like ... the world with a smartphone mounted on your head. Nevertheless, this is already a big improvement on the use of a generic HRTF.

But for those of you who do not like to compromise, we have also included a video using a setup that doesn’t require mounting a bulky smartphone on your head (DIY setup 2). Instead, it makes use of an external head tracker and a Raspberry Pi, amounting to a total investment of about 150 Euro.

how6

future setup

We are currently developing a hardware module (consisting of a head tracker and in-ear microphones) that streams all the necessary data wirelessly to your smartphone. In combination with an app that guides you through the measurement procedure, this will make it much easier (and cheaper) to measure a high quality HRTF at home.

You will see that measuring your personal HRTF, at this stage, involves some effort and adroitness. But hey, being part of a real scientific experiment is fun. And do you know anybody else who has measured the unique way in which sound waves bend around their head and ears before finding the way to their brain!

 

contact

for all inquiries:

contact@earfish.eu

who are we

jonas
Dr. Jonas Reijniers
Active Perception Lab
Universiteit Antwerpen

herbert
Prof. dr. ir. Herbert Peremans
Active Perception Lab
Universiteit Antwerpen

bart
Prof. dr. Bart Partoens
Condensed Matter Theory
Universiteit Antwerpen

fons
Fons De Mey
NEXOR
Universiteit Antwerpen