AES Settles on SOFA for 3D HRTF Datasets
If you're in the process of developing an application that virtualizes 3D audio for headphones, at some point you're going to have to settle on what you're going to use for HRTF (head related transfer function) data. You could design your own, of course, but why re-invent the wheel when there's numerous sources for high resolution HRTF datasets out there? Nah, the best thing would be to try a few of them to pick the one you like, or better yet, pick a half dozen you like and let the user select which sounds better.
Yeah, that sounds great until you realize that these datasets are in a wide variety of formats requiring you to re-program the system to interpret and create the DSP filter used during listening. Just switching from one HRTF dataset to another would be a major programming headache.
Enter SOFA, "Spatially Oriented Format for Acoustics", an effort shepherded by the Austrian Academy of Sciences, Acoustic Research Institute that lead the charge for a new standard. From their institutional project web page here:
The spatially oriented format for acoustics (SOFA) is dedicated to store all kinds of acoustic informations related to a specified geometrical setup. The main task is to describe simple HRTF measurements, but SOFA also aims to provide the functionality to store measurements of something fancy like BRIRs with a 64-channel mic-array in a multi-source excitation situation or directivity measurement of a loudspeaker. The format is intended to be easily extendable, highly portable, and actually the greatest common divider of all publicly available HRTF databases at the moment of writing.
SOFA defines the structure of data and meta data and stores them in a numerical container. The data description will be a hierarchical description when coming from free-field HRTFs (simple setup) and going to more complex setups like mic-array measurements in reverberant spaces, excited by a loudspeaker array (complex setup). We will use global geometry description (related to the room), and local geometry description (related to the listener/source) without limiting the number of acoustic transmitters and receivers. Room descriptions will be available by linking a CAD file within SOFA. Networking support will be provided as well allowing to remotely access HRTFs and BRIRs from client computers.
Evidently a lot of hard work with help from researchers at numerous educational and industry entities has resulted in a standard precise and useful enough that the Audio Engineering Society has decided to adopt it as a standard. If you're a member of the AES you can download "AES69-2015: AES standard for file exchange - Spatial acoustic data file format".
Pretty esoteric stuff. Should you care? Well, from my point of view it provides a key element in portable HRTF datasets...and that means the possibility of using any HRTF you might choose, even your own! Yes, with a standard like this in place I can definitely see spending $100 to go down to your local audiologist to have your personal HRTF measured. Then you could poke it into your iPod/android and have all the 3D headphone virtualization stuff we'll see in 3-5 years using your own ears and HRTF. And that could make these virtual audio features eerily effective.