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HRTF doesn't matter for headphones, only IEMs

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funkmeister:
I'm calling it! HRTF is BS for headphones. poo

My main operative theory here is that the sound needs to enter the ear as similarly to natural sound as possible. I don't want to take that too far with things like crossfeed, just from an FR standpoint. It's the point of entry that matters. The whole idea of trying to replicate a human ear canal and then measuring the resultant distorted signal inside of there, then correcting the distorted FR with a compensation curve is a load of BS and a waste of time, money, and other resources. At most we only need to compensate for boundary effects a bit in developing an ideal headphone curve.

Now... HRTF matters for IEMs because if you have been hearing with your own set of ears for your entire life up to this point, and I assume you have, then an IEM which is close to your eardrum needs to be tweaked to reproduce what your head and ear canal does to sound. That's why your individual HRTF matters for IEMs but a generic HRTF may not be good enough.

So, we just need to figure out what subtle rise and fall on the FR chart is needed to keep sound from a headphone in line with natural sound. I never really claimed that making things sound like good speakers was the way to go, but having heard what the Harman researchers have to say about it (thanks Tyll for sharing), I've adopted the thinking that it's the perfect place to operate in terms of research.

I made the case for rethinking HRTF in a few places about a year ago and people got defensive and made it into a fight because HRTF was untouchable and they went on trying to educate me all about it. Well... I think the whole concept needs to be rethought.

donunus:
HRTF matters if headphones are measured with the microphone inside the ear near the eardrums. You are partly right though. If you think about it, we can get a more simple approximation bu putting the mic and measuring from outside the ear a cm or so. hmm lets wait for Purrin and the other measurement experts to chime in

Marvey:
It depends upon the measurement method on whether to apply "HRTF" or not. Most folks over at HF, when talk of HRTF was all the rage, seem to have confused HRTF with someone much simplier: FR compensation. I guess HRTF in its most simplistic form is a base compensation. An ideal behind HRTF is that the transfer function (I bet 99% of HF has no idea what a transfer function is in mathematical terms) should be three dimensional. One way in implementing this is to use individual impulse response transfer functions based on specific angular measurements in a spherical coordinate system. In practice, one would take limited set of measurements of different azimuth and altitude, and interpolate. The idea behind this is of course to to simulate a room / venue or provide directional cues with limited number of speakers. That's key. How HRTF got misapplied to the concept of very basic FR compensation, I do not know. Probably because it sounds fancy, and if one uses fancy words or acronyms, then one must be smart.

IEMs require a compensation to boost the a narrow area around 2-3kHz. When I spoke with UE, it was their opinion that the pinna boosted that region, so compensation was required for IEMs, which of course bypass the pinna. I do feel the same way in a subjective sense. (Note that the IEM measurements on this site already compensate for this - so the measurements you see are "perceptual" rather than "raw" measurements.) The raw measurements of the UERM do show a boost in this area. The ER4 also have a boost, although the I think it's overdone. IEMs which don't have that boost in the raw measurements seem to sound too laid back with vocals, particularly female vocals. This is not necessary a bad thing. The "BBC curve" used for speaker voicing pushed 3k back to lessen exaggerated room effects from the combination of the recording venue and the room used for playback. I find the BBC curve useful for live concerts, but not so helpful with studio recordings.

Speaker measurements are done with a microphone in free air. The v1 headphones measurements on this site where done in a simulated free-air environment using a porous sponge. These measurements were combobulated with another sealed plate measurement to arrive at the correct bass.

As for compensation used here, it's rather simple. I compare to references I consider neutral: my speakers and my audiophile desktop setup (both surgically EQ'd via digital PEQ to a target FR with a slight downward slope. If no one wants to believe me that this curve yields the "best" most neutral results, just ask the Harmon researcher Dr. Sean Olive, PhD.) I think I've posted a few listening position FR graphs of those setups. People can argue all they want about HRTF, compensation curves, diffuse field, AES papers, B&K recommended curves, etc. but at least I've provided a reference - and compensated as best as I could the measurements on this site to those references. Again, the measurements here are perceptual FR graphs. And finally, several folks here have actually heard my reference setups.

But yeah, in the context of how most folks at HF use the term HRTF with measurements, it's BS.

ultrabike:
Transfer Functions and Fourier Transforms are closely related in general. However, some headphone Transfer Functions (and respective Fourier Transform) may be somewhat independent of HRTFs (specially with headphones that do not bypass the external ear).

It makes sense that realistic HRTFs are 3-D functions which may be unique to a particular individual. However, I believe performance of a sound reproduction system should be characterized relative to real world sound sources, which are independent of HRTFs. Note that speaker characterization is independent of surroundings (anechoic chamber) and head (with small mic a certain distance away from source).

One difference between speakers/sound-sources and non-IEM headphones may be that cans bypass the front of the head and fire directly to the ears. So I also believe some slight compensation (not the full HRTF measured at the ear canal) should be applied in the characterization of most headphones that do not bypass the ear. This is because many recordings target speaker reproduction. Acoustic impedance and anechoic chamber/plate emulation might be needed though.

IEMs bypass quite a few ear parts which are individual dependent, so some further compensation might be needed, and this compensation might not be 100% accurate for every individual... an average might be close. The ear might do some octave averaging to some extend, but dunno.

AstralStorm:
Actual HRTF is a 3D complex domain function, but in terms of headphone and IEM listening, only the 2D component matters, and usually only the one for 60 degrees to the side or front one, depending on which one is chosen.
The rest matters for spatializers or head tracking.
It might be that Fourier model of the head function is insufficient as the function is actually nonlinear.
Head itself is a minor part of the HRTF - the most important part is the outer ear.

Mono equalization by ear derives the frontal HRTF convolved with headphone/IEM response. Usually this is very close to the compensated measurement, perhaps with some resonant shifts and minor differences in upper midrange gain (around 3kHz) as well as ear canal resonance amount (around 6kHz).

There are still a few variables in headphones - distance from eardrum, central or off-center positioning of the driver which changes outer ear gain.
For IEMs, there's insertion depth and exact outer ear gain.

Both can also suffer from bad acoustic seal, like this:

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