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Which is the threshold for audible THD in % for untrained audiophiles ?


DuckToller
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1) Deriving from a discussion @ another thread in the DAC section with @sandyk, I'd like to invite you to a discussion whether anyone has a valid proof about the limits of hearing (standard audiophile, 60+ years, no special training in naval/sonar environment) regarding  audible THD in % ???
2) I'll use ithe thread t as well for a measured response (sort of good citizenship lesson) to Alex/SandyK's "perfomance" in the subjective section, as I had no interest to derail that informative thread with off-topic postings about his unqualified and belittling, eventually passive aggressive attitude, towards other forum members, including myself.

The basic questions:

- Which would be the threshold for an audible percentage of distortion in % THD ?
- Is the quoted value of 0,002 % THD referring to an audible distortion level in real life?
- Given these impressively low values for THD in % for modern audio gear and the fact that differences may be between 0,002% THD of one unit and  let's say 0,0035 % THD of another, can that difference of 0,0015 %  be perceived as an audible difference which an average audiophile may detect when listening to his highly resolving system ???

I am not talking about trained experts or people with special skills here.

Alex was quoting Douglas Self's Amplifier handbook trying to push audible limits from 0,25% that he claimed before to even higher levels up to 0,002% (bold from me😞

"Digital audio now routinely delivers the signal with less than 0.002% THD, and I can earnestly vouch for the fact that analog console designers work furiously to keep the distortion in long complex signal paths down to similar levels. I think it an insult to allow the very last piece of electronics in the chain to make nonsense of these efforts.

I would like to make it clear that I do not believe that an amplifier yielding 0.001% THD is going to sound much better than its fellow giving 0.002%. However, if there is ever a scintilla of doubt as to what level of distortion is perceptible, then using the techniques I have presented it should be possible to routinely reduce the THD below the level at which there can be any rational argument.

 Audio Power Amplifier Design Handbook 5th ed. - Douglas Self p.21  Extract

 

While I can understand the logical construction of Mr. Self to underline why making the highest efforts as a principle of audio engineering is valid without harming the community, his point may not precisely be about audible quality differences but about engineering, at least in my understanding.
However, I am open for correction, that's why I started the thread.

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In conjunction to Alex's postings in the other thread , I can't confirm a fit of this quotation (Self, above) for Alex's purpose as a response to the question of @motberg  "Any scientific back up to the claim 0.25% THD as tested in your example is detectable by average humans?" which came  from a user, who was interested in reading/discussing the topic of added distortion to the his signal chain by using a passive pre-amp.

What I can detect is a behavioral patter of disrespect ("I suggest that you do some research for yourself for a change. There is plenty of information available on the subject."), belittling ( #86 "Your idea of audibility may not be the same as others who may have more revealing equipment.") , smoke and mirrors  (#93)  and passive aggressive intent (#119), which altogether characterize the self defined Master Level Member's lack of respect for anyone he considers outside his bubble (perhaps as well as below his level???).
Personally, I find his behavior poisonous for the more than difficult to achieve balance in our forums, and my initial sentiment that he would continue his crusade - even he got his worst enemies removed from this site - appears to be justified.

 

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Why did I refer to smoke & mirrors in my last response to him?
While reading the informative discussion about DAC vs DAC+preamp, I've seen @motberg discussing a real life situation and having some questions concerning the response he got, especially from Alex.
I then got curious if the references used in response were specifically rhetorical or part of our Master Level Member's belief. As a consequence I asked a tid bit more specific :
"Please allow me to ask, if you believe these figures

(0,002%THD) are audible for common audiophiles (60+ years), 
the majority of whom may not have been able to meet the requirements for the job as Naval Sonar operators even at young age and therefore had to forego the special training associated with it?"

He responded with: "You don't need special training to hear distortion, unlike the Sonar requirements."
Did he really understand my phrasing the way like I've asked him if anyone from the audiophile community needs a special training to hear (common) distortion ???

I am the opinion, that I've asked him in an understandable manner, if he believes that
age group 60+ (for average audiophiles) would be generally qualified to hear these distortion levels he quoted (0,002% THD), without having the training as specialist professions which he quoted exemplary just before (and who  perhaps not even have qualified for that training in their twenties - I would guess there is a strong selection for getting trained for such jobs?)

Though, if questions like the above arrive in the discussion, it is deriving from the numbers he put into the game,
"about distortion figures, not 10 , but  >100 times less than you have stated ."
(he put in 0,002 % THD as a proof for 0,25 % that were in question related to the 0,5% that have been confirmed as audible threshold by the user who asked him)

 

Consequently, I may take from his answer, where he showed no intention to refer to the question, that he looks more qualified to discuss audible levels of distortion in general terms and that he doesn't believe that a level of 0,002 % THD is demonstrably better sound wise due to the lower distortion levels or to rephrase it: to make an audible difference to i.e. 0,0035 % THD)

 

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He continued:
"Quite a few DIY Audio members were able to hear clear differences between the different states of the attached amplifier with front end modifications. The measurements were posted in a DIY Audio thread by a member from Melbourne. "

Where exactly is anything stated in these threads from 2008 that would support your claim about 0,002 % THD being audible and answer my question more specifically for the majority of the audiophile age group 60+ ???
Actually the reference was not only from 2008 - which might give an insight in his Master Level Member's universum -  furthermore I found it completely useless in regard to the question.

 "See also : https://www.diyaudio.com/forums/solid-state/134221-silicon-chip-200watt-ld-amplifier-2.html # 13 and 15

They were also able to hear clear differences with Front End balancing as in the attached link to a DIY Audio thread where Nelson Pass was also a participant."
Another thread the MLM has participated in a long time ago, but no confirmation for Alex's claim is deriving from that, imho, only two minor questions occur:

- Can you explain what you were to going to proof with citing #15 ???
- And did Nelson Pass confirm your "estimations" you voiced in #17???

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I have no personal interest to continue the feud he had with MansR, as a consquence his MLM SandyK will come to the ignore list today. Though I prefer by heart the fun in our hobby in listening and discussing and exchanging opinions and knowledge, however I feel he may have better invested more often a 2nd thought before he misroutes other members, who obviously had personal interest in reading/discussing about that subject of distortion, with numbers that are impressive but irrelevant in the sense of audibility.

Personally, I tend to dismiss the possibility to have a fruitful discussion with Alex in the future as he shows his passive-agressive face once more in his latest aimed at me:
"
Don't bother.

I posted more than enough information already in an area where this was not deemed necessary.

I want nothing further to do with a member like yourself who has already made it crystal clear that he wishes to see me banned from the Objective area, and by the look of it the forum itself .Any replies from you to me, or quotes from me in that area will be ignored and remain unread."

 

At this point he turns the friendly request by the owner of a thread he quickly started to derange with his incivility:
"
@sandyk - 
Alex, please stay away from this thread, like forever.
I have reported all your posts in this thread to Chris with the demand to have them removed.  As en experienced user of this and other forums you know exactly why that happened. So no need to discuss your motives and excuses. However, you have the right to continue discussing the subject with me on a pm basis, if you subdue to the ground of common sense and civility. Thanks, Tom"


into a ban for the whole sub-forum. On a side note: He couldn't even control himself in PM communication.

 

To sum it up: I may have truly deserved his disagree buttons as a personal motivation when I posted in the "objective-Fi" forum in the last weeks and he may continue to use me as a target for his personal crusade as facts proof that he can't be relied upon his words.
 

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16 minutes ago, AudioDoctor said:

Untrained?

HAHAHAHA, geez

untrained in the sense of not having enjoyed a naval sonar training, as quoted by Alex as reference, like Paul R or miska, who are capable of  hearing a far wider spectrum than the ones with no sufficent system at hand and lacking  this special experience, unlike the Master Level Members:
I refer to them as common audiophiles, thus untrained. Aren't you untrained in that sense  @AudioDoctor ???

 

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Yes, it is caused by the non-linearity of the transfer function.

 

But, how it manifests is not exactly obvious from a harmonic measurement test or simulation.  A few hours in front of a spectrum analyzer measuring a multi-tone communications system will prove that to anybody who actually is interested.  No math analysis required.

 

My point is that while a simulation of pure harmonic distortion is interesting, it doesn't really replicate what happens due to that non-linearity in an actual system.  (System meaning a a bunch of components put together to produce a result - for audio, it's to eventually move some air based to stimulate a listener's aural system.)

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22 minutes ago, CG said:

Yes, it is caused by the non-linearity of the transfer function.

 

But, how it manifests is not exactly obvious from a harmonic measurement test or simulation.  A few hours in front of a spectrum analyzer measuring a multi-tone communications system will prove that to anybody who actually is interested.  No math analysis required.

 

My point is that while a simulation of pure harmonic distortion is interesting, it doesn't really replicate what happens due to that non-linearity in an actual system.  (System meaning a a bunch of components put together to produce a result - for audio, it's to eventually move some air based to stimulate a listener's aural system.)

 

I'm not arguing that harmonic distortion measurement is the best way to analyze non-linearity, in fact the opposite. My simulation, for example, creates a variable, user-controlled non-linearity and applies it to any test signal, including the best hi-res audiophile recording or a 1000 multi-tone test signal. There's no frequency-domain manipulation involved, other than to display the resulting spectrum. The non-linearity can be measured, simulated, reproduced, and in some cases, corrected. While it's best to analyze the whole system end-to-end, there is some significant value to be able to measure individual components.

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6 minutes ago, pkane2001 said:

My simulation, for example, creates a variable, user-controlled non-linearity and applies it to any test signal, including the best hi-res audiophile recording or a 1000 multi-tone test signal. There's no frequency-domain manipulation involved, other than to display the resulting spectrum.

 

Is the distortion frequency dependent in any way?

 

Slightly OT, but I'm curious...  Is there any kind of "memory" dependency available for the distortion profile?  Example: Thermal effects.

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1 minute ago, CG said:

 

Is the distortion frequency dependent in any way?

 

Slightly OT, but I'm curious...  Is there any kind of "memory" dependency available for the distortion profile?  Example: Thermal effects.

 

The simulation has a 'feedback' simulation that simulates the effect of a frequency-dependent negative of positive feedback. This is not meant to perfectly reproduce any specific device, but rather to let me play with various types and amounts of distortions and test myself if I can hear them. Jitter is another distortion that can be simulated and mixed with the effects of harmonic distortion, as an example.

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38 minutes ago, pkane2001 said:

 

The simulation has a 'feedback' simulation that simulates the effect of a frequency-dependent negative of positive feedback. This is not meant to perfectly reproduce any specific device, but rather to let me play with various types and amounts of distortions and test myself if I can hear them. Jitter is another distortion that can be simulated and mixed with the effects of harmonic distortion, as an example.

 

OK - good to know.  

 

I'm sure you know that basic device linearity is not only a function of operating conditions, intrinsic device design, but also of frequency.  That certainly would affect the results of your simulation.  (That wasn't specifically directed at you, but at people reading...)

 

Is the jitter actual phase/frequency modulation of the entire spectrum or is it simulated by adding the resulting noise sidebands to each tone?

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7 minutes ago, CG said:

I'm sure you know that basic device linearity is not only a function of operating conditions, intrinsic device design, but also of frequency.  That certainly would affect the results of your simulation.  (That wasn't specifically directed at you, but at people reading...)

 

Agreed. That's why I said this earlier:

 

1 hour ago, pkane2001 said:

%THD is mostly meaningless, as it doesn't indicate the type or shape of non-linearity that caused the distortion. What's more, this value can change with level and frequency, so a single number is just not enough to characterize the full effect or its audibility.

 

7 minutes ago, CG said:

Is the jitter actual phase/frequency modulation of the entire spectrum or is it simulated by adding the resulting noise sidebands to each tone?

 

Jitter in DISTORT is the actual timing error added to the desired test signal. The timing of each sample is adjusted in accordance with selected modulation noise/signal (from random noise to 1/f noise to configurable sine-wave frequencies, as well as correlated signal). The sidebands and other distortions produced are the result of modifying the timing of samples, these are not artificially inserted :)

 

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4 minutes ago, DuckToller said:

 

Just excellent and a suitable approach for your soon to come new system 😉

 

I sense a bit of sarcasm here, but its not that hard to hear real improvements, not the kind that I need to have a "Golden Ear" to be able to hear.

No electron left behind...

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10 minutes ago, AudioDoctor said:

 

I sense a bit of sarcasm here, but its not that hard to hear real improvements, not the kind that I need to have a "Golden Ear" to be able to hear.

Not at all, I may envy your future system a bit like I do with miguelito's dream system, but I hope I can cope with that.

Having experienced the AA horns, I am sure that you will enjoy audible improvements, however I doubt it may lead you to separate ultra-ultra low distortion levels from ultra low distortion levels.

Thoug hopefully to a deeper enjoyment of music  through the magic of low distortion, narrows dispersion & controlled directivity..

Cheers, DT

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There was a reference posted to an old paper proposing a multi-tone test for harmonic distortion. Here's a monster test signal that I'm currently using :) Not something that was easy to generate in 1978, when the paper was written! This is showing non-linearity, so plenty of harmonic and inter-modulation distortion, but all below -100dB.

 

image.thumb.png.e18aecef1ada378d9b5626e96286219f.png

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1 hour ago, pkane2001 said:

There was a reference posted to an old paper proposing a multi-tone test for harmonic distortion. Here's a monster test signal that I'm currently using :) Not something that was easy to generate in 1978, when the paper was written! This is showing non-linearity, so plenty of harmonic and inter-modulation distortion, but all below -100dB.

 

This test looks very promising.  Audio Precision offers something similar, for a price.

 

In your example, some of the distortion tones are about 65 dB below the level of the "desired" tones.  If you add the power of all these up, it really is imposing, since there's so many distortion products.  Just as the paper spelled out.

 

I'm not the guy doing the work, so this is only me wondering aloud...

 

What would be really cool is the ability to shape the amplitude profile of the tones.  My reasoning is that music and most other sound has a definite spectral profile.  You just don't find as much 19 KHz energy in your average concert or park setting compared to 2 KHz.  So, although having the test tones be equal in level certainly stresses the system, it may not be realistic enough to provide much insight to the system as a sound reproducer, as opposed to a test signal reproducer.  Probably, somewhere, somebody has compiled a representative profile of sound amplitudes under various conditions.  Maybe that curve could be a built-in option.  You could call it PK-weighting or something like that.  Be famous in your own time.

 

In communications systems, these kids of tests are often used for the reasons you suggest.  What is done is to turn off a couple of the tones and measure the level of IMD where that tone used to be.  Often, bandpass filters are used before the spectrum analyzer so that the other tones don't cause distortion within the spectrum analyzer itself.  (A real problem, btw...)

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