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Old 23rd December 2011, 12:42 PM   #21
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Is there a difference between reproduction accuracy and reproduction quality?

I'd really enjoy seeing a schematic and BOM for an AP analyzer. Good test equipment should take what's there and send it to a display; good audio equipment should take what's there and send it to a speaker.
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Old 23rd December 2011, 01:35 PM   #22
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Hi,

Quote:
Originally Posted by sofaspud View Post
Good test equipment should take what's there and send it to a display;
Wrong. Any test equipment has the job to give a precise (precision of determines cost) answer or set of quantive answers to a set of predefined qualitative questions (e.g. how much harmonic distortion).

If it answers the question accuratly it is good test equipment. If the question is wrong (as in the quality being quantified is in fact meaningless in the context in which it is employed ) it is still good test equipment, even though it is in effect an expensive boat-anchor for this particular subject. I would argue that the AP2 qualifies mostly as such an expensive boat-anchor for Audio, even though I regularly get to use one (it answers mostly the wrong questions)...

Quote:
Originally Posted by sofaspud View Post
good audio equipment should take what's there and send it to a speaker.
Why? Given what the speaker is going to do with it (distortion, compression, frequency response distortions etc. et al)? Where the point of this?

It is like the Pharisee's in the parable that Yeshvha guy told, of them straining at the gnat in their wine (that is publicly straining their wine so they would not unintentionally violate jewish dietary law; used as an illustration how the Pharisee's would make a great show of obeying small laws in public) while gulping down the camel (that is to violate grossly the same laws when out of sight).

Similarly we see here a discrimination against comparably small flaws in measured performance in the sense of traditional measurements in electronics being painted as unacceptable, while the much larger flaws of the same nature commissioned by the speaker are simply swept under the rug. Where is the sense in that?

I would suggest that good audio equipment (including speakers) should provide a realistic reproduction of a musical event and allow an easy "suspension of disbelief". This so far has not been shown to be reliably accomplished by equipment that exceeds in certain traditional measurements over other equipment.

In fact, often the reverse seems to be the case.

So either there hidden variables not accounted for by traditional measurements and views, or people just like "bad sound".

I find this latter position both unconvincing and tautological, because if people like "bad sound" then by definition this "bad sound" would be actually "good sound", as it simply means people disliking what technocrats want to push on them. So it in fact the "people like bad sound" explanation in reality underlines the "hidden variable" one, one might even successfully argue that the two are the same.

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Old 23rd December 2011, 01:44 PM   #23
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Well said, Thorsten.
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Old 23rd December 2011, 02:26 PM   #24
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Quote:
Wrong. Any test equipment has the job to give a precise (precision of determines cost) answer or set of quantive answers to a set of predefined qualitative questions (e.g. how much harmonic distortion).
I propose that the above is wrong. Show me a piece of test equipment with a "question" input. It is the operator of the equipment that performs the question and answer stuff. Again, the equipment should just show what's there. To be interpreted.
The rest of your response just means to me that you see a difference between the accuracy and quality that I began my post with.
For anyone who shares that opinion (and I really have nothing against that view tbh), then arguing against measurements (and vice versa) is futile and irrelevant.
BTW you're making a straw man of "bad sound." If quality isn't accuracy, then non-accuracy is not therefore bad sound. It could very well be "quality sound."
As for hidden and not accounted for "variables," I did not discount them, neither expressly nor implied. Progress, not perfection, is the only reasonable goal.
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Old 23rd December 2011, 02:57 PM   #25
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Hi,

Quote:
Originally Posted by sofaspud View Post
I propose that the above is wrong. Show me a piece of test equipment with a "question" input.
AP2 (semi-joking).

The question input is the actually quantety being measured, that is a Volt-Meter measures voltages, if you want to (for example) measure temperatures you first need to convert them into voltages to measure them using a volt meter.

So the questions are designed into the test gear. You cannot for example use a traditional THD & N Meter to measure TIM.

With the AP2 and many modern test instruments you instead have some hardware and some DSP which can be used for many different measurements, however there is still the need to define a question, as in "how much THD".

Quote:
Originally Posted by sofaspud View Post
It is the operator of the equipment that performs the question and answer stuff.
Not really. Let us take my previous example of the classic needle display THD&N Meter (I still have one around incidentally). The question is designed, the answer is read off.

If I want to have a different question answered (e.g. how much TIM) I cannot use this THD&N Meter, because it does not answer the question.

The key here is that test equipment can only answer pre-defined questions, generally it cannot answer questions about other quantities than these it is designed to measure.

Quote:
Originally Posted by sofaspud View Post
Again, the equipment should just show what's there. To be interpreted.
There is no such test equipment for audio I know. In all cases the question and interpretation is designed in. For example, there are some forms of distortion (I call them fuzzy distortion) that are clearly visible on an analogue 'scope with the naked eye (that is they exist in reality), yet you cannot use an AP2 to measure them...

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Originally Posted by sofaspud View Post
BTW you're making a straw man of "bad sound." If quality isn't accuracy, then non-accuracy is not therefore bad sound. It could very well be "quality sound."
That was the point I was trying to get across. If an amplifier with low measured THD sounds bad according to listeners it sounds bad. If one with high measured THD sounds good according to listeners it is good. Yet our technocratic elite here at DIYA will insist that the second item is "bad" and the first is "good".

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Originally Posted by sofaspud View Post
As for hidden and not accounted for "variables," I did not discount them, neither expressly nor implied. Progress, not perfection, is the only reasonable goal.
This I agree with, progress is desired.

As for the hidden (and so far unaccounted and therefore not measured) variable, we do find that often an amplifier with greater distortion than another is perceived as better, yet adding deliberate distortion to a "clean" amplifier usually fails to improve it's sound (try it).

This suggest that in fact the difference is not in measured distortion.

Yet people keep going on futile over low measured THD when in fact this has very little correlation with "good sound" and when most speakers have hugely gross distortion, compared even to the often maligned SE Tube Amplifier...

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Old 23rd December 2011, 04:31 PM   #26
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Quote:
Originally Posted by ThorstenL View Post
For example, there are some forms of distortion (I call them fuzzy distortion) that are clearly visible on an analogue 'scope with the naked eye (that is they exist in reality), yet you cannot use an AP2 to measure them...
Perhaps you might not be able to, but most competent engineers could. If you can see it on a scope, it will cause a difference in the frequency spectrum.
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Old 23rd December 2011, 04:44 PM   #27
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Quote:
The question input is the actually quantety being measured, that is a Volt-Meter measures voltages, if you want to (for example) measure temperatures you first need to convert them into voltages to measure them using a volt meter.
OK I have a better understanding of your analogy.
Quote:
The key here is that test equipment can only answer pre-defined questions, generally it cannot answer questions about other quantities than these it is designed to measure.
Key, yes. Definitely.
Quote:
There is no such test equipment for audio I know. In all cases the question and interpretation is designed in. For example, there are some forms of distortion (I call them fuzzy distortion) that are clearly visible on an analogue 'scope with the naked eye (that is they exist in reality), yet you cannot use an AP2 to measure them...
A concrete example of your previous statement.

The next bits directly relate to my accuracy and quality question. If reproduction accuracy is the goal, then high THD/TIM is bad.
There are countless combinations of source-amp-loudspeaker and so a thousand anecdotal opinions don't mean much to me. Testing provides the meaningful data. And every test includes a measurement AFAIK.
My own analogy, though, would be something like... some say to-may-to and some say to-mah-to, and they're using that as a basis to argue over how to make the sauce.
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Old 23rd December 2011, 04:49 PM   #28
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Sy,

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Perhaps you might not be able to, but most competent engineers could. If you can see it on a scope, it will cause a difference in the frequency spectrum.
Rest assured that you cannot directly measure it using an AP2 in either analog or digtal mode. It is not capable to be set up to give me a measurement where I can say "X" or "Y" amount of FD.

Yes, you can get indications of the presence of FD and it's audio band effects, but only indirectly and with effort (e.g. you need to know it is there, look actively for it and devise a test regime to do so, but even then you cannot be sure what caused the measured effect), but that is not what I call measuring something.

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Old 23rd December 2011, 04:51 PM   #29
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Yet seeing and interpreting those differences is what a competent engineer would call "measuring something." You certainly can call it "peanut butter and jelly" if you like, but that won't really accomplish anything. If there's a difference in the time domain, there is a difference in the frequency domain. Which one uses is a pretty trivial choice, which is why any engineer has both a scope and a spectrum analyzer.
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Old 23rd December 2011, 05:07 PM   #30
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Hi,

Quote:
Originally Posted by sofaspud View Post
If reproduction accuracy is the goal, then high THD/TIM is bad.
The first problem with your statement is the amorphous, undefined term "high". What is "high THD/TIM". What is our yardstick?

A number set on a green table?

A number derived from the human hearing to represent audibility? If so one based on the average or the worst case?

The fact is that "zero distortion" is not possible. So "low" and "high" must be seen with a point of reference.

And especially THD is an incredibly poor indicator.

Earl Geddes once posted four tracks of music. One had been subjected to a process that produced 0.1% THD, the second to one that produced 9.6% THD and the third produced 12.6%.

As it so happened, even on extremely low end gear (PC Speakers) the 0.1% THD track was instantly perceived as extremely distorted, yet even on fairly high end gear the 9.6% THD track was essentially impossible to tell from the undistorted reference with any reliability, the 12.6% THD track was identifiable as being a little too warm sounding.

So, in one case 0.1% THD is too much and in another 9.6% is inaudible, which tells us what precisely?

Quote:
Originally Posted by sofaspud View Post
My own analogy, though, would be something like... some say to-may-to and some say to-mah-to, and they're using that as a basis to argue over how to make the sauce.
Please understand that measurements provide data, not information. Information is data placed in a context.

If the context is wrong, the resulting information is wrong. Again, in my example the context is "question".

If my question is "does this device have 1) audible distortions and 2) objectionable distortions" then THD is not useful. And I would suggest that when it comes to distortion my question is the correct one and the one answered by THD&N is the wrong one.

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