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Old 4th January 2012, 08:28 PM   #551
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Originally Posted by scott wurcer View Post
Where does he discuss this one? Since no one could hear a marching band at -60dB I'm curious.
A while back, I think mainly to promote his distortion metric he had three files on-line to download that had been distorted. One with a process that produced > 10% THD, one with slightly below 10% THD and one with 0.1% THD, plus the undistorted file.

Both of the heavily distorted (measurement) files sounded essentially undistorted, but I could tell the more distorted one as being different from the original. The "low measured distortion" file was just awful..

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Old 4th January 2012, 08:54 PM   #552
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Originally Posted by CopperTop View Post
So how is it that otherwise sensible-sounding engineers are still going on about certain amplifiers sounding bad, and others sounding good, and never even enquiring as to what this arsenal of 'conventional' measurements might reveal? What is the point of this thread if it's all so perfectly straightforward?
Which thread do you mean, and which sensible-sounding engineers do you mean? All sensible-sounding engineers including my humble person explained many times, looking from all possible sides, that measurements that we perform depend on topology of the amp we design, and on many other factors, so for one topology one kind of measurements is needed, another kind is useless, third kind is obvious from schematic and particular parts selected, and so on.
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Old 4th January 2012, 09:33 PM   #553
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Originally Posted by Steve Eddy View Post
In short , different nonlinearities are differently perceived by the auditor,
or said otherwise , not all kind of distorsions have the same effect on
sound perception....

Is that new ?....
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Old 4th January 2012, 09:38 PM   #554
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T, I have not closely followed the Geddes thread or papers, but he makes a point IF he can show something that measures 'bad' sounds OK, and something that sounds much 'better' sounds awful.
We were confronted by this by ABX, years ago, where what he called 'grunge' was virtually all 2'nd harmonic, and nobody could hear it easy. That is the way, often, with ABX testing. You always have to be 'on your guard' with it.
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Old 4th January 2012, 09:41 PM   #555
jcx is online now jcx  United States
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we do have a collision of world views going on in several different domains

hopefully most engaged in the hardware end of audio at least start from the "Scientific Rationalism" corner of global world views

but its not possible to build up from 1st principles complete descriptions of any technological device of any utility

some will then seize on this “gap” – claiming that since you don’t “really understand” then “anything “ could be possible

there are much bigger “gaps” in Physical Acoustics than in EE understanding of audio amplifiers – the transducers, mics, loudspeakers have much more complicated interaction with the sound fields they sense, reproduce than we have to deal with in the electrical signals they use in between

then to get to “sound” you have to add rooms, and the musical event recording

It is probably fair to say the Science has a very fuzzy “knowledge” at all of human perception

why is it that anyone could expect “simple” answers to such an ill posed question as (amplifier) measurements vs sound?

but do seem satisfied with simple "cheap shots" that agree with their prejudices
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Old 4th January 2012, 09:42 PM   #556
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Originally Posted by CopperTop View Post
A thought experiment: could you devise an amplifier circuit that passed all the usual tests (low distortion, flat frequency response etc.) but sounded terrible? My initial thought is an amplifier with some sort of in-built dynamic range compressor. What tests could guarantee to reveal the presence of the offending circuitry?
here in Coppertops post is the worded contradiction of measurement vs listening.

Although not quite terrible a Quad 405 is a good candidate, it measures close to perfect
but sounds, very much less so.... why ?

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Old 4th January 2012, 09:49 PM   #557
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Originally Posted by john curl View Post
Please do not confuse monaural and stereo phase.
I do not. My point is that our ears/brain system is sensitive to something other than just amplitude and frequency that can assist us with at least localization. That leaves time and phase. Ohm's acoustic law is frequently and improperly applied to a broader set of situations than he was talking about.
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Old 4th January 2012, 09:51 PM   #558
Pano is offline Pano  United States
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Funny about the Quad 405. It and the 303 were part of one of my first amp A/B tests. Up to that point I really thought amps didn't make much difference. I was amazed to hear much difference there was between amps that basically "measured the same".
The 405 and 303 aren't much different, tho.
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Old 4th January 2012, 10:20 PM   #559
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Yes, which is why I pushed in this thread why on earth something as "simple" as the final amplifier, considering all the terrible things that have negative effects on the signal from mic to the speaker, would have such a significant effect on the sound. Enough to make my wife not tolerate some amplifiers playing horns, and tolerate others, never having an issue with live horns at much higher volumes.

We have had some insightful discussion of designers views on how to make a good amp. But not yet have I seen a sliver of a hint on what test I could run against an amp that fails my wife's listening test, and one that passes. This would allow one to point to the problem and fix it for all amps. In this specific case, it does not require exotic or expensive design as a mere Rotel 840 or 951 passes her subjective yes/no test, where a lot of others costing quite a bit more do not. I cam make similar subjective pass/fail on some classical guitar recordings that make the bass strings sound metallic. Very non-scientific, subjective description, but I hear it reliably. Again my original statement: If two amps sound different, at LEAST one is wrong. So, what is the difference? What distortion can cause my wife's teeth to grate and strings sound metallic? I don't know, I am just a computer systems architect, not an analog designer.

Of course, maybe subconsciously those with the talent to design very good amps may not want the world to know how theirs do less wrong.
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Old 4th January 2012, 10:39 PM   #560
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Originally Posted by wahab View Post
In short , different nonlinearities are differently perceived by the auditor,
or said otherwise , not all kind of distorsions have the same effect on
sound perception....

Is that new ?....
Basically what he was saying is that a lumped THD spec isn't a terribly meaningful metric.

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