Debate Thread: Scott's Hi-res Audio Test - Page 33 - AVS Forum
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Old 06-23-2014, 06:46 PM
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Doppler distortion would occur in any object vibrating with two or more fundamentals. The effect predates loudspeakers.

I suppose our auditory circuits know how to deal with it unobtrusively.

Hmm..

If there are two separate sources of two fundamentals, is there a doppler effect in the vibrations in the air? How does a microphone see it?

I'll be back later...


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Old 06-23-2014, 07:12 PM
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Note that some papers incorrectly called IMD "Doppler" distortion. And others pointed to several causes including cone modes and nonlinear modulation in the voice coil/magnet system. There was an article in one of the Audio magazines for a low-FMD design using multiple small drivers.
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"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
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Old 06-23-2014, 07:28 PM - Thread Starter
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Quote:
Originally Posted by arnyk View Post
Thank you for actually paying attention to the rest of the article even though it runs against your agenda, Amir.

There was an AES article responding to the Klipsch article from Roy Allison (then of Acoustic Research) that further makes many critical points about speaker FM distortion. The final conclusion was that for speakers like the AR3 FM distortion is of the same order as that from professional analog tape recorders.

Here are a few references related to speaker doppler distortion
a few references??? I think you are liable to break the forum software with one of the lengthiest posts I have ever seen!

Thanks for the list. I think I have two years of work reading through them and commenting. For now, here is a quick one from one of your references:

"When these limitations to the flutter analogy and the frequency-
weighting factor are both taken into account, the analogy
leads one to expect that for any practical cone excursions,
Doppler effect in speakers, including totally enclosed direct
radiators, will be less audible by an order of magnitude than
the flutter of a 15-ips tape machine
that meets the NAB standard.


Do you mind telling us which one of your references this quote came from?

And how what I have highlighted in red in your post is consistent with the same color in your reference? Do we not care about "audibility" than numerical values you are using to compare speaker to tape?

By the way, did you ever have trouble hearing tape Wow and Flutter with a speaker? I didn't but I must have been confused given what you are saying .

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Old 06-23-2014, 08:03 PM
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Quote:
Originally Posted by spkr View Post
For a while I thought my "hearing" is extraordinarily sensitive to notice so much distortion from input and his output. Good to know that I'm normal. If I had an amplifier like him, I would have tossed it into a dumpster in a heartbeat.

Keep in mind that he's been at this sort of thing for a while and enjoys it immensely. There are sub forums that he could take his authoritative schtick to and easily dominate the threads. He's a really smart guy and I don't believe that holds any challenge for him, nor does his own forum.

Not to disparage other sub forums or even his own, but the IQ level in this forum is subjectively higher. Hence the zest for the challenge. Plus there's ArnyK. THE nemesis. He took on months of work and testing to try and dispel a position that Arny held. Who does that?

Someone who,

  • A. has a real fear that they are mistaken in their position.
  • B. is determined to unravel Arny's heretofore unflappable resiliency.
  • C. has high intelligence, taps Google though a mind meld interface, and has a motor that runs fast enough to stay with this year round.


The point is, in the words of Robert Shaw as Col. Hessler in "The Battle of the Bulge", " The best thing possible is happening - the war will go on."


See? Anyone can do movie quotes.


Amir, before you run with my "intelligence" compliments, the last exchange we had before you ignored it and moved on to cut down the Klipsch study was a little below par. Sorry, I can only give it three and a half Emmys out of ten.


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Old 06-23-2014, 08:39 PM - Thread Starter
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Quote:
Originally Posted by Tack View Post
Not necessarily. Perhaps ArnyK heard the distortions because they were indeed audible. I guarantee that whatever he heard wasn't -80db or more like the current jitter witch hunt. Obviously it was "audible".
Well, if it was "audible" then why does he say their distortions are were already below threshold of hearing?

Quote:
Originally Posted by arny View Post
That was true pretty generally back in the 1950s, but by the late 1970s there was enough equipment (particularly power amps) that was performing with all artifacts below the threshold of hearing that it was not a truism.
Arny ran his test in 1980s which is past the 1970s decade he says nirvana was already achieved.

Quote:
Originally Posted by Tack View Post
Unfortunately urapnes, you really need to read through the posts here. Perfectly reasonable sounding sentences, upon closer inspection, are sometimes distortions themselves.
Clearly we have an example of that above. Arny says amplifiers have had distortions below audibility but then goes on to "prove indisputably" that amplifiers sound different from each other. How is that not confusing and contradictory to you? Were you aware of the details of this test and the article?

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Old 06-23-2014, 09:03 PM
 
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Quote:
Originally Posted by DonH50 View Post
Note that some papers incorrectly called IMD "Doppler" distortion. And others pointed to several causes including cone modes and nonlinear modulation in the voice coil/magnet system. There was an article in one of the Audio magazines for a low-FMD design using multiple small drivers.
In Audio systems, larger transducers are a frequent source of such; however, this is becoming a lessor occurrence with the advent of new cone materials and software based electromechanical design aids such as: FEA, BEM and others.


When it does occur, it's clearly measurable and audible (much like other cone modes) and generally thought to be a design short-coming, one to most certainly be avoided.

Last edited by dB Cookster; 06-24-2014 at 06:47 AM.
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Old 06-23-2014, 11:39 PM
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Originally Posted by amirm View Post
that amplifiers sound different from each other.
Is that what he really said? Or is it the distorted version of what he said?
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Old 06-24-2014, 12:57 AM
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Quote:
Originally Posted by arnyk View Post
There have been improvements in other areas, but Doppler distortion isn't one of them.

Dopper distortion is probably the least problem with the speaker and graph you've provided above...

It's a measurement of Bose 901 driven in excess of 95dB @ 50 Hz. It s well known that the Bose 901 utilize substantial eq for the bass-region and it is well known that it will suffer from significant distortion in the bass region even at moderate listening levels. I don't say phase modulation distortion dosn't exist, just that the graph shows the sum of all kinds of excessive distortion artifacts due to a number of unconventional design desitions in the speaker as well as it beeing driven far beyond its capability.


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Old 06-24-2014, 05:29 AM
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Quote:
Originally Posted by DonH50 View Post
Note that some papers incorrectly called IMD "Doppler" distortion. And others pointed to several causes including cone modes and nonlinear modulation in the voice coil/magnet system. There was an article in one of the Audio magazines for a low-FMD design using multiple small drivers.
FM distortion is minimized by:

(1) Large diaphragm areas (planar speakers) or the use of waveguides (horns) that have the effect of acoustically increasing the effective size of the diaphragm.

The latter effect is why Klipsch came into the discussion - his Klipschorns had low FM because the LF horn acted like an acoustic transformer. Ironically, Klipsch probably sold more Cornwalls and Heresys which were essentially direct radiators at low frequencies.

(2) Operation of the speaker drivers over narrower frequency bands.

In modern times using subwoofers and upper range speakers that are 3 way instead of 2 way tends to decrease FM distortion.
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Old 06-24-2014, 05:31 AM
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Originally Posted by hevi View Post
Dopper distortion is probably the least problem with the speaker and graph you've provided above...

It's a measurement of Bose 901 driven in excess of 95dB @ 50 Hz. It s well known that the Bose 901 utilize substantial eq for the bass-region and it is well known that it will suffer from significant distortion in the bass region even at moderate listening levels. I don't say phase modulation distortion dosn't exist, just that the graph shows the sum of all kinds of excessive distortion artifacts due to a number of unconventional design desitions in the speaker as well as it beeing driven far beyond its capability.
Your facts are correct but they miss the major cause of FM distortion in Bose 901s - they were full-range 1-way speakers where the same diaphragm reproduced the lowest bass and the highest treble.

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Old 06-24-2014, 05:32 AM
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Originally Posted by spkr View Post
Is that what he really said? Or is it the distorted version of what he said?
I'll be generous and call it a "Half-truth". ;-) As presented it is regrettably half false. The whole truth is the some amplifiers sound different but a lot of them sound the same.

I wonder how low a person's IQ has to be to read "The whole truth is the some amplifiers sound different but a lot of them sound the same." and perceive: "All amplifiers sound the same". I'm thinking double digits. ;-)
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Old 06-24-2014, 05:38 AM
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Quote:
Originally Posted by RayDunzl View Post
Doppler distortion would occur in any object vibrating with two or more fundamentals. The effect predates loudspeakers.

I suppose our auditory circuits know how to deal with it unobtrusively.
To some degree. We do hear FM distortion if it is large enough. However the threshold of hearing for FM distortion seems to allow our ears to avoid busying our brain with many natural examples of it.


Quote:
Originally Posted by RayDunzl View Post
If there are two separate sources of two fundamentals, is there a doppler effect in the vibrations in the air? How does a microphone see it?
If you have a 2 way speaker and the two frequencies are exclusively divided between the two drivers, then FM distortion is vastly reduced.

That's what the microphone in everybody's lab says, because the motion of its diaphragm is usually too small for its Doppler distortion to be much of an issue.
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Old 06-24-2014, 05:48 AM
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Originally Posted by amirm View Post
Well, if it was "audible" then why does he say their distortions are were already below threshold of hearing?
Because life is often not totally simplistic. On the bench with a resistive load and within their nominal ratings both power amps had distortion below the threshold of hearing. In actual use, one of the amplifiers when connected to certain fairly demanding speakers vastly underperformed reasonable expectations based on the bench tests. It is likely that the amps were indistinguishable with other speakers. The design of the underperforming amplifier was modified by its manufacturer to correct this problem. We had a very early production version of it.


Quote:
Originally Posted by amirm View Post
Arny ran his test in 1980s which is past the 1970s decade he says nirvana was already achieved.
Again, life is not totally simplistic. In the 1970s we had a goodly number of SS amps (some documented at http://home.provide.net/~djcarlst/abx_pwr.htm ) whose distortion under reasonable conditions was below the threshold of hearing.

A few exceptions don't totally disprove a good rule. They just tell you to be on your toes. ;-)


Quote:
Originally Posted by amirm View Post
Clearly we have an example of that above. Arny says amplifiers have had distortions below audibility but then goes on to "prove indisputably" that amplifiers sound different from each other. How is that not confusing and contradictory to you?
I suspect that most people with IQs in the triple digits can figure stuff like this out if they really try. ;-)
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Old 06-24-2014, 07:03 AM
 
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Quote:
Originally Posted by amirm
Clearly we have an example of that above. Arny says amplifiers have had distortions below audibility but then goes on to "prove indisputably" that amplifiers sound different from each other. How is that not confusing and contradictory to you?

Arnyk
I suspect that most people with IQs in the triple digits can figure stuff like this out if they really try. ;-)


dB Cookster -


I initially 'liked' your IQ comment above, I thought it was witty; however, it seems now, like you were just maneuvering, to get out of the path of his question.


His statements as noted above, are reasonable. In that you have inferred that you're IQ is in the triple digits, perhaps you will chance answering his inferred double digit IQ question, head-on?
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Old 06-24-2014, 07:39 AM
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Throwing fuel into the fire?
Let Amir and Arny duke it out on this "no win" debate.
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Old 06-24-2014, 08:30 AM - Thread Starter
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Quote:
Originally Posted by spkr View Post
Is that what he really said? Or is it the distorted version of what he said?
If you didn't read the rest of my post, I can see how you are confused by that. So let me repeat again what Arny had said:

Quote:
Originally Posted by arny View Post
That was true pretty generally back in the 1950s, but by the late 1970s there was enough equipment (particularly power amps) that was performing with all artifacts below the threshold of hearing that it was not a truism.
The uninitiated will read that and think that if by 1970s we had achieved amplification "with *all* artifacts below the threshold of hearing" that by now, we must be a thousand times better yet. So any solid state amplifier I buy, will be transparent.

For 30 years, this evidence was hidden from view that amplifiers that had these *measured* specs:



weren't transparent after all arriving in this conclusion in double blind ABX tests with Arny himself one of the participants:



Now we see that it was "obvious" that the one amp would not be the one the authors wanted in their system. They only knew that after they ran their double blind test. According to "our" test data, the implication that amplifiers were perfected in 1970s, were proven officially to not be the case. And the authors were proud to declare that in their headline.

And the cause of artifacts not being below threshold of hearing? Arny explains it here and now:

Quote:
Originally Posted by arnyk View Post
Because life is often not totally simplistic. On the bench with a resistive load and within their nominal ratings both power amps had distortion below the threshold of hearing. In actual use, one of the amplifiers when connected to certain fairly demanding speakers vastly underperformed reasonable expectations based on the bench tests.
This is the message I have been trying to communicate to unfortunately deaf ears for the last few months in a number of amplifier threads. That real speakers with real music can present loads that are more difficult than simple bench testing conditions. Sadly we read the opposite in countless forum posts. Here is one from my esteemed colleague and mentor Arny:

Quote:
Originally Posted by arnyk View Post
Imagine what you will, but audio gear does not require big power supplies to effectively amplify musical and dramatic audio signals because of the high crest factor that these signals always have. Old school equipment with big heavy power transformers and heat sinks so that they are able to amplify high powered pure sine wave signals on the test bench are basically a waste of iron aluminum in actual use.
Simply said, Arny is saying that bench tests are a more difficult situation for an amplifier than real music. After 32 years we uncover evidence from Arny and crew's own tests that says otherwise as confirmed by Arny today.

As if there were any doubts, Arny says the same more crisply in yet another post:

Quote:
Originally Posted by arnyk View Post
In terms of demand and stress on amplifier components like power transformers and heat sinks, the single pure tone is a far bigger load [than music] and produces far more stress.
Surely you have heard the "crest factor" argument that attempts to justify any amount of amplification power to be good enough:

Quote:
Originally Posted by arnyk View Post
The crest factor of music means that an AVR that can operate 2 channels at a certain power level and laod impedance with sine waves, may be able to operate 7-8 channels with music.
That didn't happen in Arny's double blind test now did it? The amp that output over 200 watts with resistive bench load, couldn't muster putting out music "below threshold of audibility."

As you see even a person like me with two digit IQ can see that we have built up these pseudo scientific "technical" arguments we dump on the other camp hoping they know less about electronics and audio systems than we do. Most of the times that is the case. But once in a while you do have to reckon with your own data that says otherwise. Arny said it best:

Because life is often not totally simplistic.

No better sentence has been written than this from our three digit IQ mentor. Audio is simple until it isn't. Run off with just the simple version and one day, 32 years later, your own data invalidates the view you have propagated in those three decades across literally tens of thousands of posts in countless forums. As the line in my favorite movie Good Will Hunting went, I don't know much, but I do know that.

So if I were you, I would listen to Arny here and now. Read the headlines in his articles. And oh, don't dismiss "double blind ABX" test results and instead rewash arguments created by laymen pretending to know audio design from reading forum posts. If you do, Arny will put in you in double digit IQ group. Imagine sitting right next to me in that regard!
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Old 06-24-2014, 10:39 AM
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Quote:
Originally Posted by arnyk View Post
That was true pretty generally back in the 1950s, but by the late 1970s there was enough equipment (particularly power amps) that was performing with all artifacts below the threshold of hearing that it was not a truism.
Quote:
Originally Posted by amirm View Post
If you didn't read the rest of my post, I can see how you are confused by that. So let me repeat again what Arny had said: The uninitiated will read that and think that if by 1970s we had achieved amplification "with *all* artifacts below the threshold of hearing" that by now, we must be a thousand times better yet. So any solid state amplifier I buy, will be transparent.
Quote:
Originally Posted by arnyk View Post
Interesting Amir how many significant details disappear when you pretend to quote me.
Yup. The level of distortion between input and his output is so bad that the details get erased. Even Amir wouldn't use that kind of amplifier for his sound system. Ugh!
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Old 06-24-2014, 11:03 AM
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Originally Posted by amirm View Post
No better sentence has been written than this from our three digit IQ mentor. Audio is simple until it isn't.
I would have thought that someone with a 3 digit IQ, would be capable of understanding how to set reference levels correctly.

Perhaps you are being to nice!
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Old 06-24-2014, 12:31 PM - Thread Starter
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Quote:
Originally Posted by arnyk View Post
http://d3se566zfvnmhf.cloudfront.net...95/aes7994.pdf

Audio Engineering Society Convention Paper 7994

Characterising Studio Monitor Loudspeakers For Auralization by Ben Supper

"
So, for example, a six-inch cone in a sealed box
radiating 60Hz at 90 dB SPL has an excursion of (1.2 ×
0.63) / (60² × 0.018) = ±1.2 cm. This is equivalent to
±1.6 samples of delay at 48 kHz.
"

1 sample @ 48 KHz is equal to jitter of about 20 microseconds, 20,000 nanoseconds, or 20,000,000 picoseconds. Hence the insanity of worrying about a few 100's picoseconds of jitter.
Hi Arny. Thanks for that reference. It is a good read on how to simulate the sound of a speaker (distortions and all) using headphones.

I have a problem though that I need your help to resolve. If you read past that bit of math you have quoted, this is what the author says:

Using the equation given in Beers and Belar [2] , the
distortion of a 1kHz sine tone played simultaneously
from the same drive unit as the 60Hz, 90dB sine tone
calculated above would be 1.30 × 1000 Hz × 0.012 m =
15%. This is above the 2% threshold of audibility for a
pure tone that is stated in their paper, and also above
that anecdotally stated by Klipsch [3].

However, two sine tones is a very critical signal for
Doppler distortion, and one which is rarely encountered
in normal listening circumstances. The audibility of
distortion is highly dependent of the kind, as well as the
amount, of distortion introduced. Informal listening tests
revealed that the effect of Doppler distortion was
unnoticeable on simulated systems with six-inch drive
units
, when the low-frequency roll-off of these systems
was considered. This was true even when its influence
was artificially doubled. We therefore left it out of the
final run-time simulation [of speakers with headphones]
.


So the distortion that you are saying will dwarf others as far as audibility is stated as not being important at all in your reference.

Unfortunate your read of what you quoted is also incorrect. Delay is not jitter. The author is explaining that Doppler effect can be modeled as a delay per frequency. That is a constant and frequency dependent delay. It is not "jitter" or else the equation you quoted wouldn't give you a fixed "delay" value.

Let's remember that there is a big difference between distortions created by a speaker in a room and the exact same distortion created electronically upstream. Non-intuitively, the latter is far more audible! Yes, they are identical distortions but the nature of psychoacoustics and how the sound travels in a room makes them very different from audibility point of view.

If you like to learn more, I wrote an article on audibility of room reflections which has a reference by a listening test to examine the above:

".... Clark in 1983 set out to test to create four different scenarios that involved comb filters:

1. Using two speakers playing a mono signal. The second speaker’s sound combines with the first creating comb filtering.
2. A reflector held vertically to the right of the listener and in between him and the speaker. While the distance there was shorter than typical wall reflection, the reflection nevertheless creates comb filtering just the same.
3. Same as #2 but the reflector held horizontally.
4. Creating the comb filter electronically by delaying the signal and combining it with itself. This is the same thing I did in my earlier simulation.

Pay attention to #4 . Here is the results of the listening test for that:

"The most surprising was scenario #4 where the outcome was “greatly degrading effect.” Let me repeat: the same distortion created electronically and sent out of the speaker was a very negative thing. The reason is that when comb filtering is created that way, we don’t get the nice benefit of the image widening, or the psychoacoustic factors that reduced its severity. "

Clark summarizes thusly:

“Two speaker mono was considered superior to the one speaker, one path mono. A reflection from a vertical surface was barely audible but a horizontal reflector was more audible. An electronic delay comb filter was highly audible and annoying.


Hopefully I haven't lost everyone . Summarizing, "comb filtering" that is caused by room reflections was considered a nice effect (not the distortion people think in forums). Taking the same distortion and putting it upstream electronically, caused "highly audible and annoying" effect.

What this means is that "jitter" in upstream devices will be a very different animal than "jitter" created by a speaker and room combination. This is another reason why this made up argument of "your speakers are terrible so don't worry about the rest of the system" is just wrong. It is an argument that is designed to convince the layman while completely ignoring how we perceive sound and how the room and speakers interact.

Respectfully, your low IQ patron.
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Old 06-24-2014, 12:58 PM
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Quote:
Originally Posted by amirm View Post
Hi Arny. Thanks for that reference. It is a good read on how to simulate the sound of a speaker (distortions and all) using headphones.

I have a problem though that I need your help to resolve. If you read past that bit of math you have quoted, this is what the author says:

Using the equation given in Beers and Belar [2] , the
distortion of a 1kHz sine tone played simultaneously
from the same drive unit as the 60Hz, 90dB sine tone
calculated above would be 1.30 × 1000 Hz × 0.012 m =
15%. This is above the 2% threshold of audibility for a
pure tone that is stated in their paper, and also above
that anecdotally stated by Klipsch [3].

However, two sine tones is a very critical signal for
Doppler distortion, and one which is rarely encountered
in normal listening circumstances. The audibility of
distortion is highly dependent of the kind, as well as the
amount, of distortion introduced. Informal listening tests
revealed that the effect of Doppler distortion was
unnoticeable on simulated systems with six-inch drive
units
, when the low-frequency roll-off of these systems
was considered. This was true even when its influence
was artificially doubled. We therefore left it out of the
final run-time simulation [of speakers with headphones]
.


So the distortion that you are saying will dwarf others as far as audibility is stated as not being important at all in your reference.
Thanks for pointing that out, Amir. It makes any concern over those dwarfed levels jitter even less rational.
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Old 06-24-2014, 02:34 PM
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Originally Posted by amirm View Post
"The most surprising was scenario #4 where the outcome was “greatly degrading effect.” Let me repeat: the same distortion created electronically and sent out of the speaker was a very negative thing. The reason is that when comb filtering is created that way, we don’t get the nice benefit of the image widening, or the psychoacoustic factors that reduced its severity. "

Clark summarizes thusly:

“Two speaker mono was considered superior to the one speaker, one path mono. A reflection from a vertical surface was barely audible but a horizontal reflector was more audible. An electronic delay comb filter was highly audible and annoying.”
With the acoustic case, wouldn't the combing effects be different with each ear while in the electronic case be the same? If only one ear was allowed to listen, would the result have been different? Also this is combing, which is an additive amplitude effect, while Doppler is a frequency modulation effect.

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Old 06-24-2014, 03:06 PM
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Quote:
Originally Posted by TVOD View Post
With the acoustic case, wouldn't the combing effects be different with each ear while in the electronic case be the same? If only one ear was allowed to listen, would the result have been different? Also this is combing, which is an additive amplitude effect, while Doppler is a frequency modulation effect.
It couldn't be that Amir realizes that he's lost the FM distortion controversy, so he's trying to distract people into a discussion of AM distortion effects?
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Old 06-24-2014, 04:43 PM - Thread Starter
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Originally Posted by arnyk View Post
Thanks for pointing that out, Amir. It makes any concern over those dwarfed levels jitter even less rational.
You are welcome Arny. Alas, that is not the correct conclusion. As you said so well, life is not always simple.

You picked a distortion in speakers which has very specific characteristics. Your analysis ignored all of that and proceeded to compare it to jitter in electronics. Dismissing the audibility of Doppler effect is not the same as dismissing upstream distortions. Here again is one of your references:

"In a tape machine or record player [amir: or AVR DAC] the entire frequency spectrum is subject to
modulation at the flutter[amir: jitter] rate.
In a speaker system only that
part of the spectrum reproduced by the woofer is subject to
significant FM,
as Beers and Belar pointed out; the magnitude
of FM sidebands varies directly with the higher, modulated frequency.
A crossover frequency of 1 kHz in a two-unit speaker
system thus limits the maximum FM sideband distortion to a small
fraction of what it would be in a tape machine whose percentage
of flutter was equal to the percentage of Doppler frequency shift."


There is a lot of complexity here. If you want to be a human psychoacoustics model, then you need to incorporate all aspects of these distortions in that envelop. Ignoring them completely in the case of speakers, then going all the way to the other side for electronics while favoring an online point of view, has no basis in proper analysis.

So are we done with this argument that "speakers generate so much distortion that up stream distortions don't matter?"
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Old 06-24-2014, 04:50 PM - Thread Starter
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Quote:
Originally Posted by TVOD View Post
With the acoustic case, wouldn't the combing effects be different with each ear while in the electronic case be the same?
Exactly. That is one of the reasons why the same distortion in electronics is heard differently than one produced in the room.

Quote:
Originally Posted by TVOD
If only one ear was allowed to listen, would the result have been different?
Partially but there are other factors as I explained in the article. For example your face acts as an acoustic shadow with respect to higher frequencies which means the reflected sound and direct sound will arrive at that ear differently. The brain realizes that and extracts what is common between them.

Quote:
Originally Posted by TVOD
Also this is combing, which is an additive amplitude effect, while Doppler is a frequency modulation effect.
I used the example of comb filtering because it demonstrates the concept of electronics distortion not being equal to acoustic distortions of exact same kind. That relationship likewise holds for frequency modulation in speakers. See an example of that in the response I just wrote to Arny.
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Old 06-24-2014, 05:17 PM
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Partially but there are other factors as I explained in the article. For example your face acts as an acoustic shadow with respect to higher frequencies which means the reflected sound and direct sound will arrive at that ear differently. The brain realizes that and extracts what is common between them.
But in that case, such as timing and response differences between paths, the acoustic effects are external to the speaker. In the case of distortion created by the speaker, wouldn't that be similar to if the distortion was created by the signal driving the speaker?
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Old 06-24-2014, 05:26 PM - Thread Starter
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Quote:
Originally Posted by TVOD View Post
But in that case, such as timing and response differences between paths, the acoustic effects are external to the speaker. In the case of distortion created by the speaker, wouldn't that be similar to if the distortion was created by the signal driving the speaker?
No because the "doppler" distortion is one of woofer (due to its much higher excursion). Upstream jitter distorts all frequencies and distorts higher frequencies ones proportionally more. That distortion would be played not only with the woofer but the mid and tweeter sections. Whereas with doppler you would have only had the woofer.

Then consider the fact that woofer frequencies are not very directional. Doppler effects weakens or goes away at different directions. What you hear is the sum total of direct+indirect sound. That means that the doppler distortion gets diluted by the other reflections that have reduced amounts of it. Frequency modulation in the upstream electronic device is the same in all directions when produced by the woofer. So it doesn't get subjected to same dilution. The reflected and direct sounds all have the same distortions.

Net, net, the acoustic nature of Doppler effect is quite significant in the way it modifies its audibility.
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Old 06-24-2014, 07:29 PM
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Throwing fuel into the fire?
Let Amir and Arny duke it out on this "no win" debate.
ratman,
Don't be so cynical. What you are witnessing is an unprecedented level of stick-to-itive-ness.
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Old 06-24-2014, 08:00 PM
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High stakes are involved. The participant who receives the most "likes" for his/her posts will win the following:

- a roll of special edition bitcoins stamped with the AVSforum logo accompanied by certificate of authenticity signed by Scott Wilkinson
- eleven inches of moderately high capacitance/low inductance Monoprice speaker wire signed by Scott Wilkinson
- instantaneous advancement to the never before held rank of "addicted member" with "oak leak clusters"


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I would have thought that someone with a 3 digit IQ, would be capable of understanding how to set reference levels correctly.

Perhaps you are being to nice!
Truism!
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Old 06-24-2014, 10:03 PM
 
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[QUOTE=amirm;24730940]Quote:

Let me quote International Telecommunication Union (ITU) document that is the bible of testing for small impairments in BS1116:

"It should be understood that the topics of experimental design, experimental execution, and statistical analysis are complex, and that only the most general guidelines can be given in a Recommendation such as this. It is recommended that professionals with expertise in experimental design and statistics should be consulted or brought in at the beginning of the planning for the listening test."

This is a 30 page document describing many aspects of proper controlled listening tests and it still says that it is just scratching the surface and that qualified people need to be consulted before running head long into such testing.

"3.1 Expert listeners
It is important that data from listening tests assessing small impairments in audio systems should come exclusively from
subjects who have expertise in detecting these small impairments. The higher the quality reached by the systems to be
tested, the more important it is to have expert listeners."

"The outcome of subjective tests of sound systems with small impairments utilizing a selected group of listeners is not
primarily intended for extrapolation to the general public. Normally the aim is to investigate whether a group of expert
listeners, under certain conditions, are able to perceive relatively subtle degradations but also to produce a quantitative
estimate of the introduced impairments."

"3.2.1 Pre-screening of subjects
Pre-screening procedures, include methods such as audiometric tests, selection of subjects based on their previous
experience and performance in previous tests and elimination of subjects based on a statistical analysis of pre-tests. The
training procedure might be used as a tool for pre-screening.

The major argument for introducing a pre-screening technique is to increase the efficiency of the listening test. This must
however be balanced against the risk of limiting the relevance of the result too much."

"3.2.2 Post-screening of subjects
Post-screening methods can be roughly separated into at least two classes; one is based on inconsistencies compared
with the mean result and another relies on the ability of the subject to make correct identifications."

"4.1 Familiarization or training phase

Prior to formal grading, subjects must be allowed to become thoroughly familiar with the test facilities, the test
environment, the grading process, the grading scales and the methods of their use. Subjects should also become
thoroughly familiar with the artefacts under study. For the most sensitive tests they should be exposed to all the material
they will be grading later in the formal grading sessions. During familiarization or training, subjects should be preferably
together in groups (say, consisting of three subjects), so that they can interact freely and discuss the artefacts they detect
with each other."


dB Cookster-


These excerpts are sufficient (without additional commentary) for use in disqualifying all past, present and most probably all future ABX listening tests, from being viewed as a scientifically objective, measurement metric, of such subtleties! I am surprised, to have discovered that they have been given such weight, within many of these forums. A curious occurrence, for certain!

Last edited by dB Cookster; 06-24-2014 at 10:13 PM.
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