How much can we learn about headphones from measurement graphs?

Submitted by lr_science t3_100188n in headphones

I’m curious about measurements, largely beyond frequency response. I’m a data scientist / cognitive scientist and would like to get an overview of what measurements reflect which quality in a headphone. I’m also interested in the limits of how much measurements can really tell us. For example, with frequency response, you look at the graph and you get a good idea of the timbre of a headphone, as well as potential problem areas. But timbre is only one aspect of the sound. I’m going with the assumption that our ears and brains are nothing but measurement tools, and thus every difference that can be heard can in theory also be measured. I will however accept that limitations in the measurement equipment we use and our knowledge about the mapping between measurements and perception may limit how much we can learn about a headphone from graphs alone. This is precisely what I’d like to explore a little bit.

(1) To get an overview, let’s list perceived qualities of headphones (and I’m trying to keep orthogonal qualities separate): [A] Timbre, [B] soundstage (size, location), [C] imaging (precision of positioning, separability of instruments), [D] cleanliness and [E] dynamics / response speed / punchiness. I’m leaving out detail retrieval on purpose as I believe it to be a combination of amount of treble, cleanliness and dynamics. I’m not sure about “naturalness” of sound and whether that is a separate quality from the others. I’m also not quite sure if cleanliness is truly separate from dynamics. Am I forgetting any perceivable qualities, or am I confounding orthogonal (separate) qualities?

Now to how we measure these...

(2) [A] Timbre: Maps largely to frequency response (with a decent amount of smoothing applied).

(3) [B] Soundstage: If I understand this right, RTINGS compares the frequency response in the 1-15 kHz region to some target response, but I’m not quite sure how this works exactly. Can someone explain?

(4) [C] Imaging: RTINGS measures this as a combination of amplitude, phase, and frequency mismatches between the left and right side, as well as group delay.

(5) [D] Cleanliness: What I mean here may map to harmonic distortion. RTINGS performs a frequency-weighted HD rating.

(6) [E] Dynamics: This is not part of the RTINGS tests, but based on my experience it is a distinct quality. What I mean here could be described as speed / transient response / punch. How much fast transients (e.g. snares / click sounds) stand out, how quickly the headphone goes all silent once the signal is back down at 0, and difference in amplitude between the input signal and headphone output (i.e., compression factor or something like that -- I hope you understand what I mean). I feel like these are different aspects, but can be summarized in the "dynamics" term, just like imaging combines multiple facets in one term.

Bonus questions:

(7) The FR graphs we’re used to looking at are all smoothed by a certain amount. This can mask thin spikes in either direction in the graph. A headphone with completely smooth FR might look to have the same FR after smoothing as a different headphone with a lot of narrow and tall spikes. I’m assuming the differences between these two hypothetical headphones would be audible. Or more generally, a headphone with a lot of tiny spikes might sound a little weird? Why are FR graphs commonly smoothed quite a lot?

(8) Why is the only graph people ever seem to talk about here frequency response, and everything else is conveyed in fairly vague language?

(9) Some people strongly oppose EQing headphones. What unwanted side effects can come up and which measurements would they affect?

Enlighten me! :)

Happy new year!

edit: To be clear, I'm not asking what we can learn from frequency responses. I'm asking mostly about all the other measurements that can be made and how they correspond to the perceived qualities of headphones precisely because frequency response obviously isn't everything.

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bbuky01 t1_j2ez1ij wrote

I think you can look at all the graphs you want but I do not think they will tell how they sound by the graph. What I mean is Grado sound like Grado’s and Sennheiser sounds like a Sennheiser’s and not sure a graph can tell you which other than knowing the the headphone specific response could you tell I don’t think it accounts for tone.

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TheFrator t1_j2f7nz9 wrote

Hey! Also a data scientist reporting in. I'm passionate about headphones and have spent a lot of time reading forums and watching videos on the topic. Frequency response is the only measurement that matters for headphones (CSD and waterfall are useless).

Measured frequency response (at least for over ears) will not match exactly what you hear because the measurement rig has a different anatomy than your ears.

This is a graph of 40 different peoples perception of FR, and the divergence starts at 1Khz.

So how a headphone looks on its FR, and how it is perceived by the individual, is subjective.

Check out the paper: https://vbn.aau.dk/ws/portalfiles/portal/227875122/1995_M_ller_et_al_AES_Journal_a.pdf

Now assuming your headphone is tuned to the same target by referencing a measurement rig, they still sound different. I'm with Resolve as far as explaining as to why- the reason being diaphragm material. I've EQ'd my HD660 to my LCD-5 stock FR and vice/versa using Crinacle's paid graphing tool. And they just sound different- especially in the leading edge (attack) and decay of notes as well as the LCD-5 imaging is far more accurate (the HD660 is blobish).

I recommend trying two separate headphones and EQing them to the same target and you'll experience that they sound differently in areas other than tonal balance.

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covertash t1_j2fkshx wrote

Replying to bbuky01 (#1,241,755)

To be fair, I think what we hear can indeed be measurable. It's the interpretation of the data, and relevance/applicability with our own unique HRTF's that is one of the major missing links.

Similar to how I would buy a pair of shoes, it would be nice if I could pop in a few measurements of my ears and head, and be able to spit out results that tell me what kind of headphones or speakers I might like. Just like a pair of shoes though, you still need to "wallk a mile" in them to really determine how well they "fit" you, but it would be much less haphazard and aimless. Perhaps one day.

The main issue I have with a lot of the hubbub is the stance that "all of audio is a solved problem" because of our current body of measurements, which I vehemently disagree. And throwing out subjective discussions entirely, because we cannot reliably correlate it with the data, is definitely the wrong way to go about furthering our overall understanding if we want to have any hope in achieving the above hypothetical future.

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blargh4 t1_j2fs7kb wrote

In practice, less than we'd like. I would apply the same caveats you would looking at a speaker frequency response measured in someone else's living room. The acoustics of the tiny "room" your head/ears create in conjunction with a given headphone (to say nothing of the subjective qualities thereof) could be quite different. But measurements made on the same rig are useful for gauging the overall tonal differences between two cans... to a point - for example, to my ears my AKG K371s have some very prominent peaking near 6khz I don't see on any measurements made on the GRAS artificial heads.

I've yet to see compelling evidence that at normal listening volumes "dynamics" is something separate from frequency response and your usual illusory differences that have nothing to do with the actual sound.

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lr_science OP t1_j2fxmua wrote

Replying to TheFrator (#1,245,160)

Thanks for your response! I've read parts of that paper now and it's interesting, albeit only concerned with FR. I'm aware that different ears have different signal modulations and that paper shows this quite well (although I wish the plots were digital color images to see individual traces). However, "finding the perfect tune" isn't my concern here.

>Frequency response is the only measurement that matters for headphones (CSD and waterfall are useless).

This is much more what I'm after -- why are they useless in your opinion?

>I recommend trying two separate headphones and EQing them to the same target and you'll experience that they sound differently in areas other than tonal balance.

Yes, that's my starting point for this. Precisely because there is more to a headphone than timbre, I want to know how these things can be measured. RTINGS measures a bunch of things (as listed in the first post), although none of that relates to dynamics, and a few things aren't perfectly clear to me, plus I don't know how agreed upon their methods are in the headphone world.

BTW my comparison was between the 990s and 1990s, which have very comparable timbre, but the 1990s have what I would describe as a larger dynamic range, faster response, better imaging, and cleaner sound. Or the other way around, the 990s sound a little lush and sluggish in comparison.

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