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CD-R and Audio Hardware => Audio Hardware => Topic started by: Speedskater on 24 April, 2013, 03:19:14 PM

Title: Perception and Measurement of Headphone Sound Quality
Post by: Speedskater on 24 April, 2013, 03:19:14 PM
Sean Olive has a new blog page.

"The Relationship between Perception and Measurement of Headphone Sound Quality"

http://seanolive.blogspot.com/2013/04/the-...eption-and.html (http://seanolive.blogspot.com/2013/04/the-relationship-between-perception-and.html)
Title: Perception and Measurement of Headphone Sound Quality
Post by: benski on 24 April, 2013, 03:35:45 PM
The headphones aren't specifically identified in the findings, for obvious reasons. 

Judging by the frequency response graphs, and comparing them to the graphs on headphone.com, here is my best guess

hp1 - Audeze
hp2 - V-MODA
hp3 - k550
hp4 - k701
hp5 - bose QC15
hp6 - beats

Feel free to correct me if I'm wrong!
Title: Perception and Measurement of Headphone Sound Quality
Post by: dhromed on 24 April, 2013, 04:57:52 PM
Quote
marketing B.S. (Before Science)


he he he he
Title: Perception and Measurement of Headphone Sound Quality
Post by: chicks on 24 April, 2013, 05:10:04 PM
The headphones aren't specifically identified in the findings, for obvious reasons.


He links to S&V mag, http://www.soundandvisionmag.com/blog/2012...udio-story-2012 (http://www.soundandvisionmag.com/blog/2012/12/31/biggest-audio-story-2012) who give it their best guess.
Title: Perception and Measurement of Headphone Sound Quality
Post by: benski on 24 April, 2013, 05:19:56 PM
The headphones aren't specifically identified in the findings, for obvious reasons.


He links to S&V mag, http://www.soundandvisionmag.com/blog/2012...udio-story-2012 (http://www.soundandvisionmag.com/blog/2012/12/31/biggest-audio-story-2012) who give it their best guess.


From the article - " it looks to me like the clearly preferred headphone was the Audeze LCD2, followed by the AKG K701 and (surprise!) the Bose QC-15"

There's no way that the Bose QC15 aren't HP5.  Look at the characteristic "bump" around 30Hz, and the steep rise up to it.

(https://dl.dropboxusercontent.com/u/4289641/HA/QC15.png)

and compare to

(https://dl.dropboxusercontent.com/u/4289641/HA/hp5.png)

HP5 is the only response graph with that same bump.
Title: Perception and Measurement of Headphone Sound Quality
Post by: extrabigmehdi on 24 April, 2013, 06:34:26 PM
It's obvious that the HP1 is the audeze, because of the statement : "Most preferred headphone in sound
quality is the least preferred in comfort".
It is well known that the audeze is heavy, and somehow the "blind test" is flawed.
Title: Perception and Measurement of Headphone Sound Quality
Post by: solive on 24 April, 2013, 08:31:26 PM
The headphones aren't specifically identified in the findings, for obvious reasons. 

Judging by the frequency response graphs, and comparing them to the graphs on headphone.com, here is my best guess

hp1 - Audeze
hp2 - V-MODA
hp3 - k550
hp4 - k701
hp5 - bose QC15
hp6 - beats

Feel free to correct me if I'm wrong!


You're wrong on 5 out of 6  Send checks made out to me for the right answers
Title: Perception and Measurement of Headphone Sound Quality
Post by: solive on 24 April, 2013, 08:39:13 PM
It's obvious that the HP1 is the audeze, because of the statement : "Most preferred headphone in sound
quality is the least preferred in comfort".
It is well known that the audeze is heavy, and somehow the "blind test" is flawed.


We admitted up front that comfort/tactile factors were not eliminated from the test, and in that sense the test wasn't blind. However, our listeners didn't know which brands and models headphones were being tested so unless they could recognize the specific brand/model by its weight/comfort alone,  their judgments weren't influenced by brand, price,etc

We thought about anesthetizing subjects from the neck up to eliminate these tactile/weight factors but our lawyers wouldn't go for it
Title: Perception and Measurement of Headphone Sound Quality
Post by: IgorC on 24 April, 2013, 08:44:46 PM
Interesting article. It will be even better with some classic Sennheiser pairs.   
I'll be happy with any of those headphones, except beats.
Title: Perception and Measurement of Headphone Sound Quality
Post by: godrick on 24 April, 2013, 09:13:13 PM
I wonder which of the following is correct:

hp1 - k550
hp2 - k701
hp3 - Audeze
hp4 - V-Moda
hp5 - bose QC15
hp6 - beats

An interesting test.  From what little I understand, the B&K house curve derived in 1974 still reflects the preferred loudspeaker room frequency response.  Dr. Olive or others, any thoughts on trying to test headphones equalized or not to the B&K house curve, or using a methodology similar to B&K to derive a preferred frequency response for headphones?
Title: Perception and Measurement of Headphone Sound Quality
Post by: extrabigmehdi on 24 April, 2013, 09:57:38 PM
Here is my guess, based on user comments only.

hp1: audeze lc2. ( worst for comfort, excellent bass extension)
hp2: k701 (thin bass, bright, wide soundstage)
hp3: vmoda crossfade (comfy,  good spectral balance)
hp4: k550 (best soundstage for the remaining closed cans, good spectral balance).
hp5:bose qc15 (comfy, bad spectral balance).
hp6: beats studio ( colored, boomy, worst spectral balance)

edit: swapped vmoda & bose , as expect the vmoda to have a better spectra balance.

The study doesn't consider other measurements beside freq response such like:  impulse response, square wave response, thd+ noise .....
Title: Perception and Measurement of Headphone Sound Quality
Post by: dhromed on 25 April, 2013, 04:16:42 AM
In practical terms, i.e. when buying some phones for actual money; can we safely conclude that frequency graphs like the ones on Headroom are adequate indicators of sound quality?
Title: Perception and Measurement of Headphone Sound Quality
Post by: extrabigmehdi on 25 April, 2013, 07:58:04 AM
In practical terms, i.e. when buying some phones for actual money; can we safely conclude that frequency graphs like the ones on Headroom are adequate indicators of sound quality?


A "neutral" frequency response, is the first thing that people ask when looking for a headphone.
But it's not enough to warrant good sound quality.
In other hand, you'd see people rejecting some headphones models , just by looking at the frequency responses.
It's the case of the expensive denon d7100, there's an important bass emphasis, if you look at he graph.
Title: Perception and Measurement of Headphone Sound Quality
Post by: zheka on 25 April, 2013, 12:01:58 PM
Dr. Olive dropped a few hints about  identity of the headphones here and in the comments over at his blog.

According to him, the following list contains only one correct entry:

hp1 - Audeze         
hp2 - V-MODA         
hp3 - k550         
hp4 - k701         
hp5 - bose QC15         
hp6 - beats


This one has three correct entries (http://seanolive.blogspot.com/2013/04/the-relationship-between-perception-and.html?showComment=1366731545044#c3892194798723791075)  :

HP1 - LCD-2 (Audeze)
HP2 - K701
HP3 - Crossfade (v-moda)
HP4 - K550
HP5 - Bose
HP6 - Beats

There are three entries in both lists that match:
HP1, HP5 and HP6

I am confident that the correct one is HP1(Audeze). This makes the H5 and H6 in the second list wrong, taking 2 out of three "wrong" spots.
Out of the remaining 3 - two must be right and one must be wrong:

HP2 - K701
HP3 - Crossfade (v-moda)
HP4 - K550

we also know that none of the remaining three can swap places because it would make 2 "wrongs" which cannot happen. The Bose or the Beats must be swapped with one the three. 

with this in mind, my list is as follows

HP1 - LCD-2 (Audeze)
HP2 - K701
HP3 - Bose
HP4 - K550
HP5 - Beats
HP6 - Crossfade (v-moda)

EDIT: the first three match the S&V guess (http://www.soundandvisionmag.com/blog/2012/12/31/biggest-audio-story-2012). They did not assign the last three. Note that the S&V guys use the same measuring gear (G.R.A.S. 43AG ear simulator) that was used for the study.
Title: Perception and Measurement of Headphone Sound Quality
Post by: chicks on 25 April, 2013, 12:17:04 PM
You're wrong on 5 out of 6  Send checks made out to me for the right answers


So, Dr. Olive, which headphones do you use? 
Title: Perception and Measurement of Headphone Sound Quality
Post by: xnor on 25 April, 2013, 01:09:33 PM
I've seen him wearing K550's about a year ago in a podcast. 
Title: Perception and Measurement of Headphone Sound Quality
Post by: markanini on 25 April, 2013, 01:16:31 PM
In practical terms, i.e. when buying some phones for actual money; can we safely conclude that frequency graphs like the ones on Headroom are adequate indicators of sound quality?


Shure SRH440 & Grado SR60
(https://hydrogenaud.io/imgcache.php?id=cb7b938c835372c4a82d4100ba8d9afd" rel="cached" data-warn="External image, click to view at original size" data-url="http://i.imgur.com/RuaWTzV.png)
(https://hydrogenaud.io/imgcache.php?id=9d630db69d76692291499ab3bb48e8fc" rel="cached" data-warn="External image, click to view at original size" data-url="http://www9.pcmag.com/media/images/210766-shure-srh440-vs-grado-sr60.gif)

Denon AH-D7000
(https://hydrogenaud.io/imgcache.php?id=60fadfcf0544f4a0f7efe44e81c5bfa6" rel="cached" data-warn="External image, click to view at original size" data-url="http://i.imgur.com/Ywyb4G6.png)
(https://hydrogenaud.io/imgcache.php?id=f8c3c0339b1cba55c91b5f6559000959" rel="cached" data-warn="External image, click to view at original size" data-url="http://reviewed-production.s3.amazonaws.com/attachment/aed262e6dfb06a31fe05e9a60a1825e65f4e346e/freq.jpg)

All made using professional head and torso simulator equipment costing thousands of dollar, yet the graphs differ. There's simply no consensus on measurement and calibration standards at the moment.

EDIT:Images fixed
Title: Perception and Measurement of Headphone Sound Quality
Post by: DVDdoug on 25 April, 2013, 01:17:13 PM
Quote
In practical terms, i.e. when buying some phones for actual money; can we safely conclude that frequency graphs like the ones on Headroom are adequate indicators of sound quality?
Yes, unless there is audible distortion.

Ethan Winer (http://www.ethanwiner.com/audiophoolery.html) identifies four things that affect/describe sound-reproduction quality:
Noise
Distortion
Frequency Response
Time Based Errors

Headphones don't generate any noise (other than mechanical noise when you move the cord, etc.), and they don't generate time-based errors either.  Distortion & frequency response are the only things left.
Title: Perception and Measurement of Headphone Sound Quality
Post by: xnor on 25 April, 2013, 01:37:28 PM
All made using professional head and torso simulator equipment costing thousands of dollar, yet the graphs differ. There's simply no consensus on measurement and calibration standards at the moment.

Your links are broken and I disagree. Look at the raw data. Differences at the very low end are due to seal problems (see different raw curves at innerfidelity), difference at high frequencies are due to placement.
Title: Perception and Measurement of Headphone Sound Quality
Post by: solive on 25 April, 2013, 02:20:01 PM
Dr. Olive dropped a few hints about  identity of the headphones here and in the comments over at his blog.

According to him, the following list contains only one correct entry:

hp1 - Audeze         
hp2 - V-MODA         
hp3 - k550         
hp4 - k701         
hp5 - bose QC15         
hp6 - beats


This one has three correct entries (http://seanolive.blogspot.com/2013/04/the-relationship-between-perception-and.html?showComment=1366731545044#c3892194798723791075)  :

HP1 - LCD-2 (Audeze)
HP2 - K701
HP3 - Crossfade (v-moda)
HP4 - K550
HP5 - Bose
HP6 - Beats

There are three entries in both lists that match:
HP1, HP5 and HP6

I am confident that the correct one is HP1(Audeze). This makes the H5 and H6 in the second list wrong, taking 2 out of three "wrong" spots.
Out of the remaining 3 - two must be right and one must be wrong:

HP2 - K701
HP3 - Crossfade (v-moda)
HP4 - K550

we also know that none of the remaining three can swap places because it would make 2 "wrongs" which cannot happen. The Bose or the Beats must be swapped with one the three. 

with this in mind, my list is as follows

HP1 - LCD-2 (Audeze)
HP2 - K701
HP3 - Bose
HP4 - K550
HP5 - Beats
HP6 - Crossfade (v-moda)

EDIT: the first three match the S&V guess (http://www.soundandvisionmag.com/blog/2012/12/31/biggest-audio-story-2012). They did not assign the last three. Note that the S&V guys use the same measuring gear (G.R.A.S. 43AG ear simulator) that was used for the study.


You gentlemen are too clever for me !! 
Title: Perception and Measurement of Headphone Sound Quality
Post by: markanini on 25 April, 2013, 02:25:27 PM
Your links are broken and I disagree. Look at the raw data. Differences at the very low end are due to seal problems (see different raw curves at innerfidelity), difference at high frequencies are due to placement.

If you'll look at the graphs you'll see its more than just the low and highs.
Title: Perception and Measurement of Headphone Sound Quality
Post by: solive on 25 April, 2013, 02:37:07 PM
You're wrong on 5 out of 6  Send checks made out to me for the right answers


So, Dr. Olive, which headphones do you use? 


I don't actually wear headphones very often except when traveling on a plane or doing listener training (http://www.harmanhowtolisten.blogspot.com).

For planes I used in-ear headphones. I used to be a fan of Etymotic ER4's, but I find them to be  too thin in the bass.

I recently received a pair of AKG K3003's as part of an award I received from my employer.

I honestly haven't found an ideal headphone yet. I think there is room for improvement.
Title: Perception and Measurement of Headphone Sound Quality
Post by: solive on 25 April, 2013, 02:39:59 PM
Quote
In practical terms, i.e. when buying some phones for actual money; can we safely conclude that frequency graphs like the ones on Headroom are adequate indicators of sound quality?
Yes, unless there is audible distortion.

Ethan Winer (http://www.ethanwiner.com/audiophoolery.html) identifies four things that affect/describe sound-reproduction quality:
Noise
Distortion
Frequency Response
Time Based Errors

Headphones don't generate any noise (other than mechanical noise when you move the cord, etc.), and they don't generate time-based errors either.  Distortion & frequency response are the only things left.


Actually some of the ANC (active noise cancellation) units do produce noise. It's actually a  nuisance variable when doing blind tests: if there's no music to mask it people will identify it by the noise.
Title: Perception and Measurement of Headphone Sound Quality
Post by: extrabigmehdi on 25 April, 2013, 03:54:48 PM
Headphones don't generate any noise (other than mechanical noise when you move the cord, etc.), and they don't generate time-based errors either.  Distortion & frequency response are the only things left.


What a statement.
The website innerfidelity provide different measurements for each headphones related to sound : frequency response, thd+ noise,  impulse response, 30hz square wave response, 300 hz square wave response. So basically you are saying that I  only need to look at the graph for freq response & THD +  noise to get an idea of sound quality ?
http://www.innerfidelity.com/headphone-data-sheet-downloads (http://www.innerfidelity.com/headphone-data-sheet-downloads)
And by the way, I  don't know how the graph "Electrical Impedance and Phase" depending of frequency, can be interpreted in a useful way.

Title: Perception and Measurement of Headphone Sound Quality
Post by: pdq on 25 April, 2013, 04:04:43 PM
And by the way, I  don't know how the graph "Electrical Impedance and Phase" depending of frequency, can be interpreted in a useful way.

This could be useful in explaining the interactions between the headphone and the amplifier, if the amplifier has non-zero output impedance.
Title: Perception and Measurement of Headphone Sound Quality
Post by: Nessuno on 25 April, 2013, 04:46:53 PM
A "neutral" frequency response, is the first thing that people ask when looking for a headphone.
But it's not enough to warrant good sound quality.

All the more, there's no general consensus that "neutral" means "flat". Think for example to different design choices like free field vs diffuse field equalization.
Title: Perception and Measurement of Headphone Sound Quality
Post by: DVDdoug on 25 April, 2013, 04:47:57 PM
Quote
The website innerfidelity provide different measurements for each headphones related to sound : frequency response, thd+ noise, impulse response, 30hz square wave response, 300 hz square wave response. So basically you are saying that I only need to look at the graph for freq response & THD + noise to get an idea of sound quality ?
If you see something "funny" in the square wave or impulse response that affects sound quality,  it should aso show-up in the frequency response & distortion measurements.

In theory, I suppose you could have a driver that "rings" along with flat frequency response.  But with a real-world mechanical resonance, there is normally increased amplitude at resonance.

As far as I know, Ethan Winer's list of 4 factors covers everything we can hear!

You can actually do things to mess-up a square wave without affecting the sound (such as run it through an all-pass filter to shift the relative phase at different frequencies without altering the spectral content).
Title: Perception and Measurement of Headphone Sound Quality
Post by: extrabigmehdi on 25 April, 2013, 05:42:05 PM
All the more, there's no general consensus that "neutral" means "flat". Think for example to different design choices like free field vs diffuse field equalization.

These considerations are a bit too technical for me. I  guess that when you use the word "flat", you means that it sounds "flat" to the listeners,
and not a "flat" frequency response. I  already before tried to "flatten" the freq response of a headphone, and the result is not great.
I 've never heard of free field equalization before, I  think all modern headphones use diffuse field equalization.
Title: Perception and Measurement of Headphone Sound Quality
Post by: greynol on 25 April, 2013, 06:04:55 PM
If your pinna doesn't affect the sound when wearing headphones like is does when you're listening to the world around you without headphones, then flattening the response of the phones with an EQ will not provide the desired effect.  I imagine it's also possible not to get the desired effect if the EQ adversely alters the phase.  Though many claims about sound quality as it relates to phase response seem a bit dubious to me, so I say this only tepidly.
Title: Perception and Measurement of Headphone Sound Quality
Post by: xnor on 25 April, 2013, 06:13:34 PM
From my experience phase is really a non-issue in single driver headphones. Only in multi driver head/earphones with crossovers you can see that the energy is not focused in the first peak in the impulse response.
Still, experiments with (multiple iirc) allpass filters shows that phase shifts are very hard/impossible to detect even with headphones as long as you listen to music and not some test signals.
Title: Perception and Measurement of Headphone Sound Quality
Post by: extrabigmehdi on 25 April, 2013, 07:37:21 PM
If your pinna doesn't affect the sound when wearing headphones like is does when you're listening to the world around you without headphones, then flattening the response of the phones with an EQ will not provide the desired effect.  I imagine it's also possible not to get the desired effect if the EQ adversely alters the phase.


Well my pinnas were remodeled because of cosmetic surgery.  Logically my pinnas doesn't affect sound the same way as before, but I was not aware of a change in my hearing.

Still, experiments with (multiple iirc) allpass filters shows that phase shifts are very hard/impossible to detect even with headphones as long as you listen to music and not some test signals.


Having played with different kind of eq (minmum phase & linear phase) , I'm skeptical when you say that the phase shift are undetectable.
Title: Perception and Measurement of Headphone Sound Quality
Post by: DVDdoug on 25 April, 2013, 08:02:59 PM
Quote
Having played with different kind of eq (minmum phase & linear phase) , I'm skeptical when you say that the phase shift are undetectable.
And I'm skeptical that it is detectable.

To run an ABX test, you'd need an equalizer with "normal" setting and a "linear phase" setting.  And, that switch/setting could not affect the EQ settings.  I doubt that such an equalizer exists (at least in not hardware).  It's not "fair" to compare two different equalizers.  And of course to be accepted on this forum, the test has to be blind and otherwise in compliance with TOS #8.

I don't have a reference, but it's also my understanding that tests have been done with all-pass filters (filters that alter phase relationships without alterning frequency response).
Title: Perception and Measurement of Headphone Sound Quality
Post by: extrabigmehdi on 25 April, 2013, 08:39:30 PM
To run an ABX test, you'd need an equalizer with "normal" setting and a "linear phase" setting.  And, that switch/setting could not affect the EQ settings.  I doubt that such an equalizer exists (at least in not hardware).  It's not "fair" to compare two different equalizers.  And of course to be accepted on this forum, the test has to be blind and otherwise in compliance with TOS #8.


There's the eq ddmf lp10, that allow to set the "amount" of  phase separately for each frequency band.  (i.e 0 for minimum phase, 1 for linear phase, and any values between).
  Would you consider using such eq for comparison "fair" ?
Title: Perception and Measurement of Headphone Sound Quality
Post by: xnor on 25 April, 2013, 09:29:24 PM
For all intents and purposes single driver headphones are (mostly) minimum phase, so flattening the frequency response using a linear phase EQ with pre-ringing just doesn't make sense.
And I guess we all know that minimum phase filters are "perfectly reversible". So for equalization during playback linear phase is crap imho.

On audibility of phase:
http://www.audioholics.com/education/acous...dibility-part-2 (http://www.audioholics.com/education/acoustics-principles/human-hearing-phase-distortion-audibility-part-2)

edit:
Having played with different kind of eq (minmum phase & linear phase) , I'm skeptical when you say that the phase shift are undetectable.

What does a linear phase EQ have to do with hearing phase shifts? When you compare min. with linear phase EQs you are not just comparing phase shift but also the audibility of pre-ringing.

There's the eq ddmf lp10, that allow to set the "amount" of  phase separately for each frequency band.  (i.e 0 for minimum phase, 1 for linear phase, and any values between).  Would you consider using such eq for comparison "fair" ?

Just use a min. phase EQ that has an all pass filter.
Title: Perception and Measurement of Headphone Sound Quality
Post by: extrabigmehdi on 26 April, 2013, 07:30:47 AM
For all intents and purposes single driver headphones are (mostly) minimum phase, so flattening the frequency response using a linear phase EQ with pre-ringing just doesn't make sense.
And I guess we all know that minimum phase filters are "perfectly reversible". So for equalization during playback linear phase is crap imho.


Well, does a minimum phase eq allows to  cancel the phase from the headphones ? If not, they may just add more phase, and using "linear phase" still makes sense.
And regarding the "pre-ringing", it can be minimized by using enough smooth eq curve which means , you don't try to "flatten" exactly the freq response.

But I don't try to "flatten" the freq curve anyways. According to headroom website:

Quote
A "natural sounding" headphone should be slightly higher in the bass (about 3 or 4 dB) between 40Hz and 500Hz. This compensates for the fact that headphones don't give you the physical punch or 'impact' that the sound waves from a room speaker have; so a slight compensation for increased bass response is needed for natural sound.

Headphones also need to be rolled-off in the highs to compensate for the drivers being so close to the ear; a gently sloping flat line from 1kHz to about 8-10dB down at 20kHz is about right. You'll notice all headphone measurements have a lot of jagged ups & downs (peaks & valleys) in the high frequencies; this is normal and mostly due to reflection cancellations in the folds and ridges in the outer part of the ear. Ideally however, the ups and downs of the frequency response should be fairly small and average out to a flat line. Large peaks or valleys over 3kHz in width usually indicate poor headphone response, and should be viewed as a coloring of the sound. Some small dips in the highs may actually be desirable and should exist in the 2kHz to 8kHz region.


http://www.headphone.com/learning-center/t...easurements.php (http://www.headphone.com/learning-center/technical/about-headphone-measurements.php)


Title: Perception and Measurement of Headphone Sound Quality
Post by: Arnold B. Krueger on 26 April, 2013, 08:19:09 AM
Quote
In practical terms, i.e. when buying some phones for actual money; can we safely conclude that frequency graphs like the ones on Headroom are adequate indicators of sound quality?
Yes, unless there is audible distortion.

Ethan Winer (http://www.ethanwiner.com/audiophoolery.html) identifies four things that affect/describe sound-reproduction quality:
Noise
Distortion
Frequency Response
Time Based Errors


Ethan's presentation of this matter lacks rigor and therefore encourages a certain amount of discussion that has limited benefits.

The three (3)  things that affect sound reproduction quality are:

Linear distortion, which includes both frequency and phase response
Nonlinear distortion, which includes both amplitude distortion and time-domain distortion
Noises that are uncorrelated with the signal which includes random noise and deterministic noises.

Quote
Headphones don't generate any noise (other than mechanical noise when you move the cord, etc.),


The ultimate noise floor of headphones comes from the environment, which is the Brownian Motion of air molecules.

The noises you describe above are "Noises that are uncorrelated with the signal which includes random noise and deterministic noises". Mechanical noise is largely deterministic.

Quote
and they don't generate time-based errors either.


Except they do. Headphones with moving diaphragms are prone to generate some measurable amount of FM distortion which is nonlinear distortion and is time-based.

Quote
Distortion & frequency response are the only things left.


I submit that headphones like almost everything else in life generate some measurable amounts of the the three things I listed above.  Now we can quibble whether my list has 3 elements or six elements (if we count the internal breakdown of each of the three points).

Behind the 3 points lies decade after decade of an development of an established technology (Audio) composed of principles, doctrine, tests and criteria. For example nonlinear distortion has the potential to add new frequencies, while linear distortion does not. Some flinch at the apparent oxymoron "Linear Distortion" but if you compare and contrast linear and nonlinear distortion, you grow wiser and more empowered.

This is all consistent with the publications and wisdom of the audio arts as handed down in various refereed publications over the decades.  I think we do better trying to understand the wisdom of the giants whose shoulders we stand than to ignore them and their work.
Title: Perception and Measurement of Headphone Sound Quality
Post by: markanini on 26 April, 2013, 08:30:46 AM
extrabigmehdi, youre not getting it. Just stop.
Title: Perception and Measurement of Headphone Sound Quality
Post by: xnor on 26 April, 2013, 08:46:48 AM
Well, does a minimum phase eq allows to  cancel the phase from the headphones ? If not, they may just add more phase, and using "linear phase" still makes sense.

As I wrote, every minimum phase system has an inverse (that is causal and stable) so yes, for example, by correcting a dip at 500 Hz with a  min. phase EQ you not only correct the magnitude but also the phase of the frequency response.

Think of minimum phase as seeing the lightning first and then hearing the thunder, and linear phase as hearing the thunder first, then seeing the lightning and finally hearing the thunder again. Linear phase still has its uses like antialiasing filters where the pre-ringing is inaudible or:


Quote
And regarding the "pre-ringing", it can be minimized by using enough smooth eq curve which means , you don't try to "flatten" exactly the freq response.

But I don't try to "flatten" the freq curve anyways. According to headroom website:

It's the same for minimum phase, hence the name minimum phase. Doing smooth adjustments obviously causes less phase shift, just like it causes little less linear phase shift/group delay/pre-ringing with linear phase filters.

The thing is that most headphones do not have such a smooth frequency response to begin with. For example, the HeadRoom graphs are heavily smoothed, resulting in the illusion that using smooth filters will fix everything.

But sure, I agree that even if you're using a limited graphic EQ you can improve most headphones.
Title: Perception and Measurement of Headphone Sound Quality
Post by: Nessuno on 26 April, 2013, 09:05:35 AM
All the more, there's no general consensus that "neutral" means "flat". Think for example to different design choices like free field vs diffuse field equalization.

I  guess that when you use the word "flat", you means that it sounds "flat" to the listeners, and not a "flat" frequency response.

I meant exactly "flat frequency response", which is a precise concept and quite easy to quantitatively assess, whereas "neutral" is a qualitative concept and subject to opinions and interpretations that often differ from listener to listener. You were speaking of frequency response and used the word "neutrality" and what I wanted to say, in other words, was that a flat frequency response measurement, which for example is considered at least a good starting point to achieve subjective neutrality for speakers, is most often considered a wrong one for headphones (edit: should you ever encounter one... ).

But from other posts you seem to know already.
Title: Perception and Measurement of Headphone Sound Quality
Post by: extrabigmehdi on 26 April, 2013, 10:58:36 AM
so yes, for example, by correcting a dip at 500 Hz with a  min. phase EQ you not only correct the magnitude but also the phase of the frequency response.

This is great news, although it would be interesting if I could study further this point. There's the dsp "bbe d82 exciter" , that claims to "compensate" phase shift.
I  guess that it's mostly a basic minimum phase eq then.

Quote
Think of minimum phase as seeing the lightning first and then hearing the thunder, and linear phase as hearing the thunder first, then seeing the lightning and finally hearing the thunder again.

Yes but if I re-use your analogy , the amount of "thunder" for "linear phase"  is reparted before and after the "lightening" : i.e 50% before and after.
But from what I've gathered,  we are more sensitive to "pre-ringing", than "post-ringing".
Title: Perception and Measurement of Headphone Sound Quality
Post by: Arnold B. Krueger on 26 April, 2013, 11:26:10 AM
But sure, I agree that even if you're using a limited graphic EQ you can improve most headphones.


That I agree with.

A lot of hand-wringing over phase is counter-productive because the ears are fairly insensitive to phase > 1 Khz as long as we are talking relatively small angles and applied to both channels identically.

The ear is also not all that sensitive to frequency response aberrations that only cover narrow bands:

http://home.provide.net/~djcarlst/abx_crit.htm (http://home.provide.net/~djcarlst/abx_crit.htm)
Title: Perception and Measurement of Headphone Sound Quality
Post by: xnor on 26 April, 2013, 02:03:02 PM
This is great news, although it would be interesting if I could study further this point. There's the dsp "bbe d82 exciter" , that claims to "compensate" phase shift.
I  guess that it's mostly a basic minimum phase eq then.

This seems to process signals in a nonlinear fashion. Anyway it is definitely not a basic minimum phase EQ.

Quote
Yes but if I re-use your analogy , the amount of "thunder" for "linear phase"  is reparted before and after the "lightening" : i.e 50% before and after.
But from what I've gathered,  we are more sensitive to "pre-ringing", than "post-ringing".

I don't think this (50% before and after) is true. A quick check with a +6 dB peak at 4 kHz with Q=1.14 shows it's more like over 80% before and 80% after (for the samples to drop to about -80 dB).
But we're definitely more sensitive to pre-ringing because it's unnatural.
Title: Perception and Measurement of Headphone Sound Quality
Post by: markanini on 26 April, 2013, 03:14:40 PM
I meant exactly "flat frequency response", which is a precise concept and quite easy to quantitatively assess, whereas "neutral" is a qualitative concept and subject to opinions and interpretations that often differ from listener to listener. You were speaking of frequency response and used the word "neutrality" and what I wanted to say, in other words, was that a flat frequency response measurement, which for example is considered at least a good starting point to achieve subjective neutrality for speakers, is most often considered a wrong one for headphones (edit: should you ever encounter one... ).

But from other posts you seem to know already.

Possible concepts to conflate don't end here.
Title: Perception and Measurement of Headphone Sound Quality
Post by: Martel on 12 September, 2013, 03:24:01 AM
Yes, unless there is audible distortion.

Ethan Winer (http://www.ethanwiner.com/audiophoolery.html) identifies four things that affect/describe sound-reproduction quality:
Noise
Distortion
Frequency Response
Time Based Errors

Headphones don't generate any noise (other than mechanical noise when you move the cord, etc.), and they don't generate time-based errors either.  Distortion & frequency response are the only things left.

What about stereo imaging of a headphone? How can you possibly judge that from a single FR chart? Even telling from two charts (one for each channel) is non-intuitive.
Title: Perception and Measurement of Headphone Sound Quality
Post by: Nessuno on 12 September, 2013, 04:55:10 AM

Headphones don't generate any noise (other than mechanical noise when you move the cord, etc.), and they don't generate time-based errors either.  Distortion & frequency response are the only things left.

What about stereo imaging of a headphone? How can you possibly judge that from a single FR chart? Even telling from two charts (one for each channel) is non-intuitive.

Frequency response, even when measured by a dummy head, is attributable only to the particular transducer and encasing used, so it characterizes objective properties, while stereo imaging depends strongly, amongst other factor, from the recording (i.e. conventional vs binaural) and the HRTF of the listener (and even expectations, experiences of live listening, mood etc... ).

Generally speaking I think stereo imaging/illusion is the least measurable or otherwise characterisable and predictable behaviour, both for headphone and speakers. It's a field where in the end only personal subjective evaluation matters.
Title: Perception and Measurement of Headphone Sound Quality
Post by: markanini on 12 September, 2013, 05:01:00 AM
Yes, unless there is audible distortion.

Ethan Winer (http://www.ethanwiner.com/audiophoolery.html) identifies four things that affect/describe sound-reproduction quality:
Noise
Distortion
Frequency Response
Time Based Errors

Headphones don't generate any noise (other than mechanical noise when you move the cord, etc.), and they don't generate time-based errors either.  Distortion & frequency response are the only things left.

What about stereo imaging of a headphone? How can you possibly judge that from a single FR chart? Even telling from two charts (one for each channel) is non-intuitive.


What stereo image? Use a crossfeed DSP.
Title: Perception and Measurement of Headphone Sound Quality
Post by: xnor on 12 September, 2013, 05:54:15 AM
Imaging with stereo recordings in headphones is a complex topic (I use to say: "there is no sound stage") since there's a mismatch between what our hearing expects and what is being output by the headphone drivers.

Based on anecdotes, that open, full-size headphones have the best imaging I'd say:
- "bigger" headphones incorporate the pinna more (IEMs bypass everything but the last part of the ear canal)
- open headphones have more crosstalk (IEMs have high isolation and seal each ear canal)

Those things result in more natural sound. Additionally, headphones with boosted bass may sound more spacious since low frequency content in stereo recordings is also closer to what our hearing expect than treble.