This is a post taking about HRTF support with the PS5 and why outside of stereo headphones, you shouldn’t set your expectations high. Why a HRTF may provide a slight improvement to speaker audio but will not sound anything like the real thing.
HRTF stands for Head Related Transfer Function. I’ve known about this for years, way before the PS5 announcement. Fundamentally they are complex frequency/phase/delay/crosstalk algorithms... with the goal of simulating 3D binaural audio the way humans actually hear it. The whole point of a HRTF is to help simulate 3D audio, generally with headphones.
We don’t have 20 ears scattered in many directions, we have 2. The way we hear sounds above us, behind us and in various directions is due to how our brain processes the sound and vibration. The field of study is called Psychoacoustics and it’s a very complex subject. To simplify this as best as I can, the auditory “processor” of the brain filters “data” in a way that it can deduce the direction, distance, size, weight, etc of a sound. Sound from above for example, travels down through the skull exciting the auditory system, many sound waves also travel around the skull multiple times and many find their way into the ear canals. The brain interprets the small delays, pressure differences, cumulative pressure, phase, attack, decay, crosstalk, etc. All these individual metrics to form a mental soundscape of what’s going on, all in real time.
Fundamentally you only need 2 sources of sound, in the form of stereo headphones. A driver for the left ear, a driver for the right ear. Theoretically this is the perfect setup (disregarding headphone type). The moment you take the sound sources away from the ears and start outputting audio from a distance is the moment the soundscape collapses.
The more speakers you add in the form of surround sound, the better the directional effects and interpolation becomes - but they are fundamentally trying to emulate 3D binaural audio. Only a 360 degree stadium of point-source speakers can match and exceed 3D binaural audio with a HRTF from headphones.
I’ve listened to a state-of-the-art £50K+ Dolby Atmos setup. Better than anything in the cinemas for raw audio quality. All calibrated by Dirac room correction in an acoustically treated room. Even then, as amazing and jaw dropping as that sounded - the level of accuracy and precision for directionality with HRTF binaural audio from good headphones still outclasses it. The quality of the components in the room were near-perfect on a technical level too.
Which also leads me onto the next part, which is to truly simulate 3D audio the way we hear it, the conditions need to be near-perfect. What do I mean? Well I’ll start with calibration. Frequency and phase response ideally should be flat (for the frequency response, flat with a gentle downwards slope), with minimal to no external colourations or reflections. Surround sound AV receivers get around this by using room correction software like Dirac, which measures and calibrates the system to render a flat frequency response, a flat phase response and partial control of resonances. If the PS5 has no audio calibration software, no ability to hook up a measurement mic and calibrate the frequency and phase response of your system that’s already a large deviation away from near-perfect. Even if Sony does develop calibration software to use a measurement mic with, the software can’t correct everything, so users need to have a decent room with acoustic treatment of some sort (like acoustic panels). Without such that’s another deviation away from near-perfect.
Not just room correction, but the PS5 ideally needs the ability to set the speaker distance. Even if using a TV, for the HRTF to even have a chance of working decently the distance between each speaker and to the listener needs to be known by the algorithm. It also should have a speaker compensation system, so that it knows the general limitations of the chosen audio output - limiting dynamic range somewhat for weak speakers like that of a TV or soundbar.
Even if the PS5 does come with excellent calibration and setup software, if you hook up a measurement mic and apply speaker/room correction, if it knows distances and compensates for speaker quality, if you have an acoustically treated room... it won’t come close to delivering true 3D audio as is supposed to be experienced binaurally with headphones. The most you will get is a slight boost to the audio quality, nothing revolutionary. If none of the above systems are in place to tune the audio, a HRTF can potentially make sound from say a TV or soundbar perceptually worse depending on the room and speakers. At its best, it will sound like the basic virtual Dolby Surround Sound found in modern TVs, only slightly better... only for the one person sat in the sweet spot with their HRTF profile. For people with AV receivers and room corrected surround sound setups, the improvement will be the same - a slight increase in quality, for the person sat in the sweet spot using their HRTF profile.
Even going back to stereo headphones, to simulate a realistic and properly working 3D soundscape things need to be high-grade. Using compressed Bluetooth audio via the controller severely limits quality. Using headphones that have a poor frequency/phase/impulse response also will impair the soundscape. To truly simulate binaural audio with your own HRTF, you will need a pair of headphones that measure well, powered by a well measuring DAC plugged in via S/PDIF Optical or USB. That could still be thrown off if Sony doesn’t create different headphone compensation profiles for the HRTF - like IEM, closed-back, on-ear and open-back profiles, etc. But if everything is set right, a high-end headphone setup will genuinely simulate what Sony claims which is truly realistic 3D audio.
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