What Causes This Output from Headphones?

[Lion♡]

let's assume that the HRTFs of 0° front and 30°

The HRTFs at 0° front and 30° are not similar. And at 30°, both ITD and ILD come into play.

translate over headphones to 180° left.

Hmm... why would that be 180°?
Is it because the headphone drivers or IEMs produce sound at 90° on both sides?
Of course, you could think of it that way, and in practice, HPTF, your ears, and each device interact in a way that might make it sound like that. However, each product is tuned differently with a specific intention, and some may be designed to replicate the HRTF of a particular angle on a specific dummy head—more precisely, the dominant listening ear (e.g., the left ear for the left speaker).
Even if a device response follows the HRTF of a specific angle, headphones and IEMs do not have crosstalk, so accurate localization cannot be achieved unless it is a binaural track.

That's why I didn’t intend to participate further in this thread.
I like speakers, headphones, and IEMs alike, but I don’t place much significance on specific targets or products—I just see them as playback devices.

Since I have my own HRTF and also correct other people's HRTFs and their corresponding BRIRs, my perspective is that HRTF is simply the frequency shape that appears when an individual hears sound from a specific angle. Following that response on IEMs or headphones, which lack crosstalk, doesn’t hold much meaning. It’s already a distortion of how we naturally perceive sound in real life.

(If you completely remove the opposite ear channel from a recorded HRIR or BRIR, you essentially get the personalized IEM/headphone target that some people seek—essentially, an ear response from a specific angle. But I don’t have any strong opinions on whether that’s good or bad. It just is.)

However, setting that aside, if the characteristics of headphones/IEMs are shaped not by interactions with the pinna but rather by internal reflections within the ear cup, then those reflections could be perceived as the unique signature of each device. This, too, will vary based on individual preferences.
Since there is inherently no crosstalk, the brain may pick up cues from these subtle reflections and perceive the sound as richer or smoother. And that’s not wrong at all.
So in the end, it all depends on what one desires, and I personally believe that it’s difficult to definitively say whether something is good or bad.

 

[Heinrich]

The HRTFs at 0° front and 30° are not similar. And at 30°, both ITD and ILD come into play.

Assumption, as to not complicate the example.

Hmm... why would that be 180°?

Wow, now you know I'm German ;-) We always do that ... . Of course 90°!

 

[Lion♡]

Wow, now you know I'm German ;-) We always do that ... . Of course 90°!

Whether it’s 90° on both sides or 180°, it’s essentially the same discussion.
Forget about specific device targets or particular responses for a moment, and think about it in a simple way—it'll be easier to understand.
When you listen to a speaker positioned at 30°, your ears receive a corresponding HRTF.
Now, you want to hear the same thing through headphones.
To achieve that, you would equalize the headphone’s response to match the 30° HRTF + the headphone’s own response.
This should, in theory, recreate the perception of 30° positioning.
Alternatively, manufacturers may take this into account and tune their products to simulate certain angles or a specific balance.
However, as I mentioned earlier, even if a device is tuned to match the 30° HRTF, that doesn’t necessarily mean it fully replicates the perception of sound coming from 30°.
The most crucial factors, ITD and ILD, are missing—so it’s really just the response of one ear at 30°, rather than the full spatial experience.
---> If the track you’re listening to is a binaural track, then it’s fine because ILD and ITD elements are already recorded into it.

So you live in Germany. I live in Korea. I'm also using a translation tool, so I appreciate your understanding.

Following that response on IEMs or headphones, which lack crosstalk, doesn’t hold much meaning. It’s already a distortion of how we naturally perceive sound in real life.

Of course, even modern standard stereo tracks contain some ILD elements to a certain extent. Listening to them without crosstalk (similar to speaker crosstalk cancellation) can have its own significance. However, unless the response fully accounts for interaction with your own ears and truly represents the HRTF of a specific angle, its meaning can be significantly diminished.

 

[solderdude]

1.) The Mystery: Just what is it that causes this???

I only see this with open headphones (on my fixture that does not add ear gain) and both I and Amir do not measure in a truly silent surrounding.
Also Amir's fixture (ear + ear canal) has a substantial gain in that frequency range which also amplifies sounds from the outside world by a good 10-20dB.
So it seems to be an effect somewhat similar to holding your hands cupped around your ears letting through some of the surrounding sounds.

Chances are if one would measure in a 'silent' box that will be smaller so a measurement error of sorts.

(Just my opinion)

 

[Lion♡]

I only see this with open headphones (on my fixture that does not add ear gain) and both I and Amir do not measure in a truly silent surrounding.
Also Amir's fixture (ear + ear canal) has a substantial gain in that frequency range which also amplifies sounds from the outside world by a good 10dB.
So it seems to be an effect somewhat similar to holding your hands cupped around your ears letting through some of the surrounding sounds.

Chances are if one would measure in a 'silent' box that will be smaller so a measurement error of sorts.

(Just my opinion)

The measurement data below are mdat files measured by a user from the Korean BRIR gallery. (These are not my measurements.)
I agree with your opinion on noise floor and open headphones. Measurement issues could also play a significant role.
I adjusted it to a similar standard as ASR's group delay.

HD800s

akg k712

560s

susvara


And we can also check the other things.

Sometimes, certain headphones exhibit an impulse response that appears as if it includes a very slight amount of room reverb.

The difference isn’t huge, but since headphones and IEMs generally have a lower noise floor compared to speakers, subtle reflections become easier to hear. That’s why, as I mentioned earlier, if this characteristic is not a measurement issue but rather an inherent trait of the device, people may perceive it as a signature rather than a flaw, depending on their preferences.

So, as I mentioned in my first comment in this thread, if it’s a characteristic of the device rather than a measurement issue, some may perceive it as a signature rather than a flaw. That’s why I believe it’s difficult to simply judge it as good or bad.

 

[Heinrich]

Chances are if one would measure in a 'silent' box that will be smaller so a measurement error of sorts.

(Just my opinion)

So you think that the ‚gras‘ in the group delay is an effect of outside noise during the measurement?

 

[mike7877]

Is 'smear' a word in context of sound? You address a topic that I'm especially after. The headphone shall, more or less depending on 'preference', replicate an outer diffuse soundfield around the listener in the listener's ears. Sounds more complicated than it is. What would be measured at the eardrum of the listener sitting in a diffuse soundfield, compared to what the headphone brings to the eardrum.

With headphones, other than with IEM, the ear's pinna is involved in the process. It has to do all the reflections that you may see in the groupdelay. In parts the spikes are evidence that the concept works. To remove them altogether is not a valuable target.

But the question, if all those spikes are good in that sense is another and quite valid one. Sure you know about the head related transfer function. How it really looks like is not easy to understand, because the literature mostly shows smoothed curves. In order to evaluate the referring spikes the real, detailed HRTF of the dummy head or HATS respectively as used in the measurement is needed.

Btw: planars are not as simple as the industry conveys. In contrast to what one might expect, the relatively chaotic movement of the diaphragm at higher frequencies may help with the 'diffuse' paradigm.

Now that you bring this up, the sound I believe I'm hearing is a lot like sound naturally in a room. It's a bit lively - you know how more lively rooms can steal a bit of detail? I feel like detail is being stolen in this way - it's not an exact parallel, but this is the best way I can think to describe

 

[mike7877]

You would HATE playing a real organ - the delay from key press to sound reaching you can be an order of magnitude more.

Is this relative or absolute synchronization, and if absolute, from whose point of view? Path differences for an orchestra can easily be more than 9ft. It's trickier for amplified bands with monitors I've often seen performances where I thought timing was off, but never thought about it at this level.

Maybe it's one of the less thought about functions of the conductor - to not only set the overall tempo and keep time, but keep time across the span of the orchestra. Also, the people closest to you are loudest (usually quite a bit louder) so unless you're specifically using the sound from an instrument far away(as reference), I don't think it'd happen much

 

[mike7877]

The thread link below is mine, and I appreciate your interest in it.
If I may share a personal opinion, I believe that each headphone/IEM has its own unique characteristics (or flaws), and in most cases, they work reasonably well.
But somehow... headphones feel somewhat unstable. Since the pinna is included and real-ear measurements are possible, externalization is quite easy. However, if we assume an in-room environment, it feels like a very weak reflection is applied overall in the BRIR setting.
On the other hand, IEMs can sometimes be difficult to externalize, depending on the situation. However, most IEMs perform well in their role as "playback devices."
So now, I only use Apple EarPods and Custom IEMs.
However, even if certain characteristics (or flaws) are present, whether they have a significant impact depends on the listener and the specific headphones. Some may notice them clearly, while others may not.

I think your opinion makes a lot of sense.

 

[mike7877]

View attachment 425241
View attachment 425242

The HRTFs at 0° front and 30° are not similar. And at 30°, both ITD and ILD come into play.


Hmm... why would that be 180°?
Is it because the headphone drivers or IEMs produce sound at 90° on both sides?
Of course, you could think of it that way, and in practice, HPTF, your ears, and each device interact in a way that might make it sound like that. However, each product is tuned differently with a specific intention, and some may be designed to replicate the HRTF of a particular angle on a specific dummy head—more precisely, the dominant listening ear (e.g., the left ear for the left speaker).
Even if a device response follows the HRTF of a specific angle, headphones and IEMs do not have crosstalk, so accurate localization cannot be achieved unless it is a binaural track.

That's why I didn’t intend to participate further in this thread.
I like speakers, headphones, and IEMs alike, but I don’t place much significance on specific targets or products—I just see them as playback devices.

Since I have my own HRTF and also correct other people's HRTFs and their corresponding BRIRs, my perspective is that HRTF is simply the frequency shape that appears when an individual hears sound from a specific angle. Following that response on IEMs or headphones, which lack crosstalk, doesn’t hold much meaning. It’s already a distortion of how we naturally perceive sound in real life.

(If you completely remove the opposite ear channel from a recorded HRIR or BRIR, you essentially get the personalized IEM/headphone target that some people seek—essentially, an ear response from a specific angle. But I don’t have any strong opinions on whether that’s good or bad. It just is.)

However, setting that aside, if the characteristics of headphones/IEMs are shaped not by interactions with the pinna but rather by internal reflections within the ear cup, then those reflections could be perceived as the unique signature of each device. This, too, will vary based on individual preferences.
Since there is inherently no crosstalk, the brain may pick up cues from these subtle reflections and perceive the sound as richer or smoother. And that’s not wrong at all.
So in the end, it all depends on what one desires, and I personally believe that it’s difficult to definitively say whether something is good or bad.

It all seems to get pretty complicated! If one could somehow put tiny microphones a few mm in front of a person's eardrums, play some frequency sweeps, tones, pulses, how well could that data be used for DSP for IEMs?

If you first equalized the IEMs to be perfectly flat (and they behaved nearly ideally in every other way), you could then apply the DSP which emulates the way a person's ear hears things in free space. Could be more cost effective than a full-fledged studio!

I've noticed listening loud with headphones isn't the same experience as with speakers - you can't physically feel the sound at all, it's kind of like playing a racing game on a PC with a USB steering wheel - the physics are right, but it's not the same as driving!

 

[mike7877]

I only see this with open headphones (on my fixture that does not add ear gain) and both I and Amir do not measure in a truly silent surrounding.
Also Amir's fixture (ear + ear canal) has a substantial gain in that frequency range which also amplifies sounds from the outside world by a good 10-20dB.
So it seems to be an effect somewhat similar to holding your hands cupped around your ears letting through some of the surrounding sounds.

Chances are if one would measure in a 'silent' box that will be smaller so a measurement error of sorts.

(Just my opinion)

Maybe I'm misunderstanding something, but isn't the group delay showing the length of time for the dominant tone to reach the mic though?

 

[Lion♡]

It all seems to get pretty complicated! If one could somehow put tiny microphones a few mm in front of a person's eardrums, play some frequency sweeps, tones, pulses, how well could that data be used for DSP for IEMs?

If you first equalized the IEMs to be perfectly flat (and they behaved nearly ideally in every other way), you could then apply the DSP which emulates the way a person's ear hears things in free space. Could be more cost effective than a full-fledged studio!

I've noticed listening loud with headphones isn't the same experience as with speakers - you can't physically feel the sound at all, it's kind of like playing a racing game on a PC with a USB steering wheel - the physics are right, but it's not the same as driving!

Ideally, the microphone should be placed right in front of the eardrum, but various studies and real-world user tests have shown that it works well even without such deep insertion. (For example, if we assume an insertion depth of 2, then recording with a speaker would also be 2, and recording with headphones would be 2 as well, meaning they share the same characteristics.)
Perfectly flattening the frequency response of an IEM can be quite challenging for beginners.
In that sense, headphones are somewhat easier to work with—you simply place the microphone in your ear, take measurements, and apply additional EQ adjustments if needed.
This method is applicable not only in a free-field environment but also in reverberant rooms and concert halls.
Of course, the inability to physically feel the sound is inevitable, but some people compensate for this with tactile bass transducers. Even aside from that aspect, as mentioned earlier in this thread, headphones and IEMs inherently differ from the way we naturally perceive sound—regardless of personal preference.
Compared to speakers, headphones and IEMs are positioned closer to the eardrum and produce sound in only one ear at a time, making it easy to become trapped in internalization—the opposite of externalization—causing confusion for the brain.
There are various perspectives on this, but I once asked a doctor at a local hospital, a hearing aid company, and a researcher studying binaural audio the same question:
"If a person loses hearing in one ear, how do they perceive sound?"
They explained that since the brain has already accumulated data from listening with both ears—ranging from several months to decades—it can compensate, making it seem as if the missing ear is still hearing sound.
And that got me thinking in the opposite direction.

So, if we listen with a physical barrier placed between the speakers, would the brain truly perceive it as hearing with only one ear?
If that were the case, then after recording a BRIR (which is true stereo, capturing both the primary listening ear and the opposite ear), simply muting the opposite ear’s channel would create a state where each channel is heard by only one ear, completely eliminating crosstalk.
However, this feels somewhat different from using a physical barrier.
When using BRIR that way, you really do hear the sound in only one ear.
In reality, we can’t completely seal off one ear 100%, but even if we do, our brain compensates and interprets the sound accordingly. This leads me to personally think that this might be another key difference between IEMs/headphones and speakers.
(Truly hearing sound in only one ear would only happen if we completely lost hearing in one ear and also lost all the brain’s stereo-related data associated with it.)


Therefore, the complete absence of crosstalk is both an advantage and a disadvantage of IEMs and headphones.

When crosstalk is properly accounted for and applied through HRIR/BRIR, the listening experience becomes identical to hearing speakers in a real space. Furthermore, if an XTC solution like Bacch or Race is applied on top of that, it transforms into an externalized binaural experience similar to speakers—unlike the internalized binaural effect of IEMs and headphones, where left and right channels remain fully separated.

 

[solderdude]

It all seems to get pretty complicated! If one could somehow put tiny microphones a few mm in front of a person's eardrums, play some frequency sweeps, tones, pulses, how well could that data be used for DSP for IEMs?

To use that data you would have to measure (near perfect) speakers in your room and get that as a baseline and EQ the head/earphones to that baseline when the goal is to mimic how you hear your speakers in your room.
Unfortunately this too isn't a real reference either, not even for the person using it because room effects are included.

That's why 'perfect' EQ does not exist.

 

[Lion♡]

To use that data you would have to measure (near perfect) speakers in your room and get that as a baseline and EQ the head/earphones to that baseline when the goal is to mimic how you hear your speakers in your room.
Unfortunately this too isn't a real reference either, not even for the person using it because room effects are included.

That's why 'perfect' EQ does not exist.

It depends on the room and speaker placement, but as long as a direct sound path of 4–5 ms is secured, the remaining reflections can be ignored (similar to measuring speakers without NFS).
Of course, an HRIR without reflections has limited use unless you are listening to something like a binaural track that includes both ILD and ITD, but it is still possible.
You can achieve that by applying appropriate gating and synthesizing the low frequencies.

 

[solderdude]

So you think that the ‚gras‘ in the group delay is an effect of outside noise during the measurement?

I believe that to be the partly the case. Reasoning: if it were baffle, pads or other effects it would also be seen in closed headphones and it is only observed in open headphones and only in the ear-gain part of the spectrum so I say measurement error in combination with the 'cup' around the ear that is formed by the pads and baffle that kind on 'amplifies' the effect of incoming noise.
It seems to be worst in the most 'open' headphones (usually planars) and the ones that have a lot of distortion in that range.
Could well be fan noise from the AP555 that does not seem to be far away.

Whenever I see this in GD I also observe this (the low level 'islands')

It seems to 'die' out slowly so is not 'noise in the room' otherwise it would always be there and I'm sure would mess with the GD. So it seems to be a combination of things, the open character seems to have something to do with it, maybe even damping of the driver on the rear. I don't think any of this is audible nor something to worry about.

One of the closed ones that shows this is https://www.audiosciencereview.com/...fiman-he-r10p-stealth-headphone-review.59393/ but... check the distortion plot too and the impedance plot it shows driver issues.

 

[Heinrich]

I believe that to be the partly the case. Reasoning: if it were baffle, pads or other effects it would also be seen in closed headphones and it is only observed in open headphones and only in the ear-gain part of the spectrum so I say measurement error in combination with the 'cup' around the ear that is formed by the pads and baffle that kind on 'amplifies' the effect of incoming noise.
It seems to be worst in the most 'open' headphones (usually planars) and the ones that have a lot of distortion in that range.
Could well be fan noise from the AP555 that does not seem to be far away.

Whenever I see this in GD I also observe this (the low level 'islands')

It seems to 'die' out slowly so is not 'noise in the room' otherwise it would always be there and I'm sure would mess with the GD. So it seems to be a combination of things, the open character seems to have something to do with it, maybe even damping of the driver on the rear. I don't think any of this is audible nor something to worry about.

One of the closed ones that shows this is https://www.audiosciencereview.com/...fiman-he-r10p-stealth-headphone-review.59393/ but... check the distortion plot too and the impedance plot it shows driver issues.

I see, that‘s a quite plausible explanation. Could it be also crosstalk between channels?

 

[solderdude]

I don't think so as it is seen in both 3 wire and 4 wire measurements and that would not limit itself to the ear-gain band.

 

[KSTR]

I believe that to be the partly the case. Reasoning: if it were baffle, pads or other effects it would also be seen in closed headphones and it is only observed in open headphones and only in the ear-gain part of the spectrum so I say measurement error in combination with the 'cup' around the ear that is formed by the pads and baffle that kind on 'amplifies' the effect of incoming noise.
It seems to be worst in the most 'open' headphones (usually planars) and the ones that have a lot of distortion in that range.
Could well be fan noise from the AP555 that does not seem to be far away.

Excellent point.
I had assumed that the headphones are measured in an isolation box, do we have any info from Amir about the specifics of the setup?
OTOH, depending on the test signal used there shouldn't be any singinficant issues. IME, REW with a long log-sweep (4M point FFT @ 48kHz) and several repetitions (8) REW is completely immune to non-correlated noise. If a single short sweep were used, immunity might be bad enough for random outside noise to leak through.

 

[Jimbob54]

Excellent point.
I had assumed that the headphones are measured in an isolation box, do we have any info from Amir about the specifics of the setup?
OTOH, depending on the test signal used there shouldn't be any singinficant issues. IME, REW with a long log-sweep (4M point FFT @ 48kHz) and several repetitions (8) REW is completely immune to non-correlated noise. If a single short sweep were used, immunity might be bad enough for random outside noise to leak through.

Pretty sure he has outlined his set up somewhere . Dont believe any form of isolation box deployed. Just a quiet room in the house but same room as AP.

EDIT- this was 4 years ago and not sure if its been changed since. I'm sure @amirm can clarify https://www.audiosciencereview.com/...g-into-measuring-headphones.18086/post-607663

 

[Heinrich]

I don't think so as it is seen in both 3 wire and 4 wire measurements and that would not limit itself to the ear-gain band.

Acoustical crosstalk, sorry.