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Amplifier Distortion (Bob Carver, 1973)

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Results of an informal test project on the audibility of amplifier distortion, by Bob Carver (Stereo Review, May 1973)
 
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DISTORTION is one of those specifications that every- one talks about but few really seem to understand.
For example, newcomers to the world of high fidelity frequently have the impression that distortion is something that bad amplifiers have and good ones don't. A manufacturer revises the distortion specification of one of his products from, say, 0.1 per cent to 0.05 per cent, and audiophiles immediately assume that it will now sound "cleaner" as a result. Or an engineer discovers that a product under test suffers from high "crossover" distortion at low power levels, and he immediately assumes that it will sound rotten in actual use.

Considering the efforts expended to reduce distortion to ever-lower levels, it seems curious that few, if any, engineers have ever stepped back from their test instruments long enough to ask themselves exactly what specific goal they are striving for. The difficulty, of course, is that the meters on distortion-test instruments have only numbers on them rather than such meaningful legends as HIGH, Low, and SUB-AUDIBLE. And in the absence of some definitive word from the psychoacoustics labs stating that "the trained listener is unable to hear distortion of complex program material when it is below x per cent," engineers will continue to strive onward—or is it "downward"? — for ever-lower distortion numbers.

At this point some readers may be thinking, "So what? Even if there is only a questionable advantage in lowering distortion far below the level at which it is audible, what's the harm?" Well, there is harm if the product thereby ends up costing more than it really has to, or if the money spent on lowering distortion could have been used elsewhere in the design to produce some more practical user benefits.

I have touched on these matters from time to time in my monthly Audio Questions and Answers column, and Julian Hirsch has also devoted at least one of his recent Technical Talk columns to the question of the audible effects of crossover distortion, but neither of us then had access to any hard experimental data to back up our suppositions and speculations. During a conversation with Robert Carver, designer of the Phase Linear equipment, I mentioned our interest in the subject and struck gold. It seems that he had been investigating the question of the audible threshold of distortion for years and had notes, laboratory data, and, what is more, firm opinions on the subject. But, since some of his findings seriously contradicted accepted audio dogma, he felt that, for credibility's sake, it would be best not simply to write an article (as I immediately urged him to do) telling what he had found, but rather to recapitulate, in condensed form, his original experiments for the eight "golden ears" attached to the technically oriented editors and contributing editors of STEREO REVIEW and allow us to come to our own conclusions.
 
 And so, one Saturday morning early this year, Julian Hirsch, Ralph Hodges, Craig Stark, and I came together in Craig's basement laboratory/listening room and awaited the arrival of Robert Carver, his 200 pounds of test instruments, and what turned out to be some mind-blowing revelations. The following article, with some additional explanatory notes, is Mr. Carver's description of some of what we discovered during that fascinating weekend.—Larry Klein, Technical Editor
 
 
 
THE prospect of conducting a weekend of technical demonstrations for the assembled technical editors of STEREO REVIEW caused me a certain amount of trepidation. Was I being simply perverse in trying to prove that very low distortion really wasn't necessary—when I had already designed and was marketing two super-lowdistortion high-power amplifiers? I knew what my measurements had shown and what my ears had heard, but would I be able to convince the others? Would they find some flaw in my procedures, my instrumentation, logic—or even my ears?

After I arrived at Craig Stark's home and unpacked and set up the test equipment and a specially modified Phase Linear 400 amplifier, we measured the background ambient noise level of our temporary laboratory. It was found to be a mere 31 dB—about the same level of quietness as is found in the country, far from the city, in the early morning hours. That is very quiet indeed, so there was little or no chance of masking effects interfering with our ability to hear whatever distortion was present. To "calibrate" our ears we played an excellent wide-range recording (an early English pressing of a folk-rock album, "The Pentangle," Transatlantic Records TRA 162) with, among other instruments, drums, snares, and a solo female vocalist. One side of the record was played several times so that we all became very familiar with the overall character and sonic "flavor" of the material. (The very low tracking force we used precluded audible groove damage that might result from repeated plays.) After listening for perhaps thirty minutes, the group unanimously agreed that the overall fidelity and "sound" of our system was almost awesome. Transients were clean and clear, plucked strings had a transparency that was absolutely chilling, and the low-frequency detail was superb—nothing was missing.

At this point we substituted an excellent 300-watt amplifier (made by a competing manufacturer) to convince ourselves that the Phase Linear 400 was indeed performing properly and that there was nothing in its sound quality that might somehow cloud our judgments during the experiments to follow. When we were finally able to get the output levels of the two power amplifiers exactly matched, there was absolutely no audible difference when switching between them while listening to either white noise or music. During the adjustments of the amplifiers, it was demonstrated dramatically that minute differences in volume level (sound quantity) that are too subtle to be heard as such are interpreted by the ear as "obvious" differences in sound quality. Everyone was startled by the effect — everyone, that is, except Larry Klein, who had touched upon the phenomenon some time ago in his Audio Questions and Answers column.

And so, psychologically and sonically prepared, we were all set, we felt, to deal with the big question: In what amounts and under what circumstances do the effects of distortion become audible? The additional signal sources we used for our tests included master tapes, a white-noise generator, and a variety of music with a wide dynamic range drawn from commercially available records. The speakers we used were AR-LSTs, chosen for their linearity, very wide frequency range, and high power-handling capability. An assortment of other lab instruments was employed to produce the scope photos and check the measurable data, but the basic point was not what could be measured, but rather what could be heard and how it correlated with what was measured.

OUR primary "test instrument" was the Phase Linear 400 stereo power amplifier that had been modified at the factory to have switch-selectable, pre-measured amounts of "crossover" distortion (see accompanying box). Klein, Hirsch, Hodges, and Stark assumed positions around the left-channel speaker. The amplifier, fed by a Hewlett-Packard generator, delivered a pure 60-Hz tone at a 1-watt level to the LST. The distortion switch on the Phase Linear was stepped upward:. 0.05 per cent, then 0.07, 0.1, 0.15, 0.2 — stop! There it is! 0.2 per cent. Wow!

Everyone was in agreement that there was some ever-so-slight change in the tone at 0.2 per cent distortion. The next increment was a large one — a jump to 0.75 per cent, at which point the distortion sounded like a separate buzz on top of the 60-Hz tone. It was audibly obvious, and all were in complete agreement as to its presence. Repeating the test at 4 watts into the speaker increased our perceptual sensitivity, and it was discovered that distortion of 0.15 per cent could then just barely be detected. (The STEREO REVIEW people all expressed surprise that such small amounts of distortion were audible.)

We next used two mixed tones: 60 and 7,000 Hz. At 0.15 per cent nobody heard the distortion. In fact, up to and including a level of 2 per cent, no one was certain that he was hearing distortion. However, the distortion suddenly became obvious to everyone at 2.5 per cent. It was heard as an "overlay" or harmonic tone added to the 60-Hz tone.

For the next test, three tones-60, 3,000, and 7,000 Hz—were mixed and fed to the speaker at a four-watt level. Even at 2 per cent no one heard the distortion. The lowest distortion perceptible to any of us was a whopping—and startling — 4 per cent!
Two more tests were performed, this time using music. The music was the recording of Pentangle used earlier for "ear calibration." The amplifier power output averaged about one watt. Distortion was stepped upwards as previously, and at 6 per cent we just began to detect a "strained" quality in the singer's voice. However, even at 6 per cent, distortion was not evident on the percussive instruments. It was only at 12 per cent that distortion began to affect the sound of the guitar and cymbals. Higher distortion levels caused an obvious "fuzziness" in the sound. To test the relationship of volume level to the ear's ability to detect distortion, we played the music at a very loud level with peaks exceeding 100 dB. There was no difference: distortion was again just barely audible at 12 per cent.

So far, our tests indicated that very small amounts of distortion (0.15 per cent) are perceptible if the program material is sufficiently simple—for example, a single pure, steady tone. Mixing two tones dramatically raised the threshold of perception to over 2 per cent. Three simultaneous tones, representing increasingly complex program material, resulted in a perception level of a surprising 4 per cent. With normally complex music, it was necessary to increase distortion to a full 6 per cent before it became just perceptible.

Although there were five different listeners of varying age involved in the tests, whatever distortion was present was usually heard by everyone—or no one. There was no disagreement. For example, on the single-tone test, 0.1 per cent was not perceptible to anyone, but 0.2 per cent was immediately evident to everyone.

It seems clear that, since crossover distortion levels below 6 per cent are not audible when listening to complex musical material, an amplifier whose measured crossover distortion is below 6 per cent will probably sound fine most of the time. But since distortion as low as 0.15 per cent was audible with a single test tone. we therefore set out to determine to what degree our test tone resembled anything that might be encountered in normal program material. In other words, could we find a recording that contained musical material "simple" enough to allow us to perceive distortion at a level below 6 per cent? We found one: a recording of Mozart's four horn concertos (Vanguard S-173) in which a single French horn is featured in several solo passages.
During these sections, we found that some change of tonal quality could be heard with distortion at a very low 0.35 per cent. With the distortion switched in, the horn acquired a "richer" quality, presumably because the harmonic distortion generated by the crossover notch added a little harmony (no pun). As higher levels of distortion were switched in, the added harmonics subtly changed the character of the horn, each time making it sound as if it had been exchanged for a different—though equally good — instrument. Only when the crossover distortion climbed above 12 per cent did the horn begin to sound fuzzy or "bad."
The objection might be raised that when distortion was not perceptible it was because the total "normal" distortion in the complete recording-playback chain was great enough to mask the distortion added during the experiment. However, our high sensitivity to added distortion on a single test tone and our low sensitivity to distortion with three test tones suggest that entirely different psycho-acoustic mechanisms were operating.
 
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THE human ear has a loudness-sensitivity response that is roughly logarithmic — which means that for every doubling of subjective loudness the objective power level of the sound has to be boosted ten times. It is this logarithmic characteristic that permits the ear to hear sounds over a loudness range of about ten trillion to one. In addition, the sensitivity of the ear varies not only with volume: its sensitivity to any given frequency may also be affected by the presence of other adjacent frequencies. This would explain why.increasing the number of test tones resulted in a decrease in our ability to perceive distortion. When a single 60-Hz tone was used. our ears were operating at maximum sensitivity for frequencies far away from the fundamental. Hence, it was relatively easy to hear the higher harmonics produced by the distortion components added to the fundamental. However, when the second tone was added, enough "masking" energy was present at the upper frequencies to cause the sensitivity of our ears to decrease significantly. The reduction in sensitivity was sufficient to render the distortion components inaudible until they were boosted by a factor greater than ten. This psychoacoustic masking phenomenon is well known today, and is made use of in the Dolby and some other noise-reduction systems. However, it has not generally been thought of as having any bearing on distortion perception.

In our final discussions, the editors admitted to some shock and surprise at both their sensitivity and lack of sensitivity to distortion under the various test conditions. And I pointed out, perhaps unnecessarily, that we had investigated only the most common and "worst-case" type of distortion encountered in amplifiers, that there are many other design factors that affect the sound of today's transistor equipment. However, that must await another time, another discussion, one which will include some of the other data and insights that have emerged on the question of what makes transistor amplifiers sound bad — or good.
 
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Robert Carver has taught physics at California State University. Designer of the Phase Linear equipment, he's just completed a preamp with noise reduction based on psychoacoustic masking.
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I found it interesting that, with music as a source, they had to bump the distortion to 12% for it to be audible.

 

10% is -20db down, so they're saying that anything happening below that threshold is inaudible.  This is the kind of thing I was getting at when I asked :  http://thecarversite.com/yetanotherforum/default.aspx?g=posts&m=47562#post47562

 

IOW, if power cord A ($20) and power cord B ($800) both have line residuals at least 20db down from the fundamental (guaranteed in both cases) then, even disregarding the power supply's PSRR, the audible difference between them will not be discernable by a human.

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I found it interesting that, with music as a source, they had to bump the distortion to 12% for it to be audible.

 

10% is -20db down, so they're saying that anything happening below that threshold is inaudible.  This is the kind of thing I was getting at when I asked :  http://thecarversite.com/yetanotherforum/default.aspx?g=posts&m=47562#post47562

 

IOW, if power cord A ($20) and power cord B ($800) both have line residuals at least 20db down from the fundamental (guaranteed in both cases) then, even disregarding the power supply's PSRR, the audible difference between them will not be discernable by a human.

 

Rich, I'm afraid that you are making an erronious assumption here.  Bod was discussing the ardible threshold of harmonic/crossover, not residual background noise/interference which is what most upgraded power cords address.  One has nothing to do with the other and since residual background noise and interference were not specifically addressed and that Bob did say that other factors needed to be discussed later, it might be interesting to find out if he ever studied them.

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I found it interesting that, with music as a source, they had to bump the distortion to 12% for it to be audible.

 

10% is -20db down, so they're saying that anything happening below that threshold is inaudible.  This is the kind of thing I was getting at when I asked :  http://thecarversite.com/yetanotherforum/default.aspx?g=posts&m=47562#post47562

 

IOW, if power cord A ($20) and power cord B ($800) both have line residuals at least 20db down from the fundamental (guaranteed in both cases) then, even disregarding the power supply's PSRR, the audible difference between them will not be discernable by a human.

 

Rich, I'm afraid that you are making an erronious assumption here.  Bod was discussing the ardible threshold of harmonic/crossover, not residual background noise/interference which is what most upgraded power cords address.  One has nothing to do with the other and since residual background noise and interference were not specifically addressed and that Bob did say that other factors needed to be discussed later, it might be interesting to find out if he ever studied them.

 

Yes, most power cords talk about interference or 'purity' of their filtering; what I was getting at is that BOTH line noise harmonics and crossover distortion introduce artifacts into the original signal.  Regardless of their source (crossover notches or induced EMI) they are a lower level signal than the original source ; these artifacts are therefore masked by the signal itself.

 

The science behind masking states that below a certain threshold (frequency and level dependant as shown in the link) the contribution of extraneous signal is inaudible (the masking signal will over-ride the lower level masked signal, whether it be a harmonic due to crossover distortion, a harmonic of the power supply frequency, a residual EMI signal, whatever.....)

 

The article by Bob says music will mask anything about 20db lower than itself, the article on masking seems to agree http://thecarversite.com/yetanotherforum/default.aspx?g=posts&m=47933#post47933

 

What both are getting at; the psychoacoustic phenomenon of auditory masking doesn't care whether the lower level signal is a harmonic distortion, an EMI related 'fuzz' or a pure tone; the lower level signal is masked regardless of its nature.

 

In Bob's test, pure tones were more sensitive to distortion.  In the masking test, pure tones have a narrow efficacy bandwidth.

 

In Bob's complex signal (music) tests distortions under 12% (about -20db) were inaudible.  In the masking tests, complex tones would be expected to easily mask lower level signals of -20db (as shown by the chart (just imagine a wider bandwidth due to the complex higher level signal))

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And here is J. Gordon Holt's comments about this,  from from Stereophile Posted Sep 9, 2007
 

The Great Distortion Delusion

 

By J. Gordon Holt • Posted: Sep 9, 2007
 
Hey, kids, here's the Big News. We've been deluding ourselves all along, worrying about piddling little bits of distortion that we can't hear at all. How's your preamp distortion? 1% at 1 volt out? You have a perfect preamp—a veritable straight wire with gain! That ear-shattering shrillness is all in your mind, because it has now been demonstrated that the human ear cannot perceive distortion levels of less than 6–12% on "normally complex music." If you think you can hear 0.1%, you are deluding yourself.
 
That, believe it or not, is the gist of an article by Robert Carver of Phase Linear Corp., in the May 1973 issue of Stereo Review.
 
Unfortunately, Mr. Carver was not just indulging in wishful thinking. (Phase Linear makes amplifiers and preamps!) He was reporting on the results of some listening tests that he conducted in collaboration with four golden ears from Stereo Review's staff: Julian Hirsch, Larry Klein, Ralph Hodges, and Craig Stark.

In a nutshell, here's how they went about it. Mr. Carver had had a Phase Linear 400 amplifier rigged up with a switch that introduced predetermined amounts of "notch" ("crossover") distortion to its sound. First, this group of stalwart listeners compared the Phase Linear, at the "no-distortion" setting with "an excellent 300W amplifier (made by a competiing manufacturer)," and assured themselves that "there was absolutely no audible difference" between them. Then they started the distortion tests.

First, they listened to a 60Hz tone, and found they could "just barely" detect 0.15% distortion. Yoicks!

Next, they mixed 60Hz and 7kHz, and distortion becane "obvious" at 2.5%. With a mix of 60Hz, 3kHz, and 7kHz, it took 4% distortion to be audible. Then they tried some music.

On solo voice, it took 6% distortion to be audible, and on percusaion instruments, they managed to get the distortion up to 12% before it "began to affect the sound..."

Their conclusion, which they then proceeded to "prove," was that the simpler the sound, the more audible the distortion, and conversely, the more complex the sound, the more distortion was needed in order to be audible.

The implication of this is more ludicrous than mind-boggling. What these clowns are saying, in effect, is that if you have a signal of sufficient complexity—a passage with full chorus and orchestra, for instance—the ear will become almost oblivious to distortion of any magnitude. And vanishingly low distortion is meaningful only if you wish to listen at length to sinewaves.
To those of us who know we can perceive very small amounts of distortion (and can hear differences between power amplifiers, too), all of this has a slightly Alice-In-Wonderland quality to it. The baby is really a squalling pig, and the smile lives on after the cat has gone. Things are not as they seem; perceived reality is self-delusion. In this case, though, it is Mr. Carver and his panelists who have managed to do a first-rate job of deluding themselves.

To begin with, it was obvious that the panelists, and apparently Mr. Carver too, undertook the tests with some strong preconceptions as to the outcome. The manner in which it was reported, almost smugly, that there was no audible difference between amplifiers at the outset suggests that as a group, they already unconvinced of anyone's ability to hear such things. This attitude, it seems to us, would tend to cast doubts the partiality of the listening panelists, as well as their hearing acuity.

Perhaps it was for that reason that they chose, consciously or not, to employ experimental procedures that were of dubious validity from the start.

For example, the test tones that were used were not related to one another in any musical manner They bore no more harmonic relationship than the components of white noise, which is the worst signal source one can possibly use for detecting distortion. There must be a harmonic and harmonious relationship between tones—as there is in musical sounds—in order for the ear to perceive the inharmonic products of amplifier distortion.
They were right when they attributed the rise in perceptible-distortion threshold with increasing signal complexity to masking effects, but they are wrong in assuming that the same thing happens when an amplifier is reproducing musical sounds.

In comparing musical material, the vast majority of signal information at a given instant comprises overtones, many of which are weak enough in comparison with the fundamental tones that that they should, according to Mr. Carver's observations, be effectively masked by the fundamentals. They are not, and the reason they are not is because they occupy so each more of the audio spectrum than do the fundamentals. Yet most of these overtones are mathematically related in frequency to the fundamentals of the instruments producing them, which is why live musical sound, even at tremendous volume levels, is so readily accepted as "pleasant" to our ears.

But add a little distortion—a very little distortion—to the sound of a full orchestra going full-tilt, and see what happens. Intermodulation produces sum-and-difference tones, most of which are not harmonically related to the fundamentals. The result is what the ear interprets as dissonance. The sound becomes irritating. Harmonic distortion adds new overtones that were not there originally. The sound becomes brighter and "hotter."

Mix in a typical amount of disc mistracking distortion, and the high-frequency breakup energy intermodulates against the program frequencies and splatters the distortion all the way down through the range below it.

Why didn't Mr. Carver's group observe this? Be cause the "musical" material they chose to listen to was either inharmonic in structure (percussion) or was simple enough (voice) to be relatively unaffected.

It would seem to us that the project was improperly conducted from the start. Instead of trying to prove thing cannot be done (ie, hearing minuscule amounts of distortion), they should have challenged some of the people who claim they can do it to prove that they can. Otherwise, the "experiment" becomes no more meaningful than a group of deaf people proving to their mutual satisfaction that, although sounds can be measured, people who claim to hear them are deluding themselves.
 

Who's deluding whom?—J. Gordon Holt

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And here is J. Gordon Holt's comments about this' date='  from from Stereophile Posted Sep 9, 2007
 

The Great Distortion Delusion[/quote']

I'm not a fan of Stereophile, personally, but that doesn't matter. Is it really fair to characterise the tests as having been performed by a bunch of clowns?

 
That type of ad-hominem may be entertaining (to those of like mind) but it's not persuasuve (it's the Consumer Report's Bose defense), and it frustrates an objective evaluation of the entire statement ('I've concluded these guys are clowns, you can stop thinking about it now').

This relegates everything Holt says into the realm of opinion.  Opinion without support, followed by an appeal to ridicule.

 
for example:
 
.....In comparing musical material' date=' the vast majority of signal information at a given instant comprises overtones, many of which are weak enough in comparison with the fundamental tones that that they should, according to Mr. Carver's observations, be effectively masked by the fundamentals.
 
They are not, and the reason they are not is because they occupy so each more of the audio spectrum than do the fundamentals.[/quote']
 
First, with regard to overtones altering the fundamental, Carver addresses this with the French horn test.  He doesn't ignore it.  Yes, overtones determine the character of a fundamental tone (distinguishing a french horn from a trumpet).
 
Second, Carver doesn't claim that the overtones should be masked; his panel hears differences of character in the french horn with various levels of distortion.  Stuffing words in someone's mouth, then pointing out their absurdity, isn't a realistic argument.
 
In fact, psychoacoustic experiments show that the masking bandwidth of a higher level tone is very narrow in frequency, and lower level  'overtones' are sufficiently higher in frequency from the fundamental that they should not be masked.
 
They will be masked, however, if a higher level tone, at the same frequency,  is present simultaneous with their expression (complex tones); that's just the way the human ear works.
 
.....But add a little distortion—a very little distortion—to the sound of a full orchestra going full-tilt' date=' and see what happens. Intermodulation produces sum-and-difference tones, most of which are not harmonically related to the fundamentals. The result is what the ear interprets as dissonance. The sound becomes irritating. Harmonic distortion adds new overtones that were not there originally. The sound becomes brighter and "hotter."[/quote']
 
No support for this, just opinion.  What about the observer that states "I have a low level hum during quiet passages, but everything's fine when music is playing"  Is he also a clown?  Why doesn't he hear this inharmonic distortion during music passages?  The most likely case, given the known characteristics of auditory masking,  is that the hum is being masked.
 
Similarly, it can't be rightfully concluded that the high level of distortion the panel tolerated was due to the music's harmonic relation to the distortion.
 
Holt seems to be talking about harmonic and non harmonic distortions as being either pleasant (tending to blend in) or dissonant.  This ignores the fact, for example, that all push-pull type amplifiers, solid state or tube, cancel even order harmonics; that's just by nature of the push-pull design.  The opinion that a tube amplifier is perceived as 'warm' due to its harmonic nature is not borne out by fact.
 
.....Mix in a typical amount of disc mistracking distortion' date=' and the high-frequency breakup energy intermodulates against the program frequencies and splatters the distortion all the way down through the range below it.[/quote']
 
unsupported techno-babble 
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I guess what bothered me the most is the timing difference between these two articles.  The tests were made in 1973, and the JGH article in 2007?  JGH died last year, so maybe he was getting senile.  He just got around to telling the world it pissed him off??  Maybe he's still pissed off about the Amplifier Challenge!

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And here is J. Gordon Holt's comments about this' date='  from from Stereophile Posted Sep 9, 2007
 

The Great Distortion Delusion[/quote']

I'm not a fan of Stereophile, personally, but that doesn't matter. Is it really fair to characterise the tests as having been performed by a bunch of clowns?

 
That type of ad-hominem may be entertaining (to those of like mind) but it's not persuasuve (it's the Consumer Report's Bose defense), and it frustrates an objective evaluation of the entire statement ('I've concluded these guys are clowns, you can stop thinking about it now').

This relegates everything Holt says into the realm of opinion.  Opinion without support, followed by an appeal to ridicule.

 
for example:
 
.....In comparing musical material' date=' the vast majority of signal information at a given instant comprises overtones, many of which are weak enough in comparison with the fundamental tones that that they should, according to Mr. Carver's observations, be effectively masked by the fundamentals.
 
They are not, and the reason they are not is because they occupy so each more of the audio spectrum than do the fundamentals.[/quote']
 
First, with regard to overtones altering the fundamental, Carver addresses this with the French horn test.  He doesn't ignore it.  Yes, overtones determine the character of a fundamental tone (distinguishing a french horn from a trumpet).
 
Second, Carver doesn't claim that the overtones should be masked; his panel hears differences of character in the french horn with various levels of distortion.  Stuffing words in someone's mouth, then pointing out their absurdity, isn't a realistic argument.
 
In fact, psychoacoustic experiments show that the masking bandwidth of a higher level tone is very narrow in frequency, and lower level  'overtones' are sufficiently higher in frequency from the fundamental that they should not be masked.
 
They will be masked, however, if a higher level tone, at the same frequency,  is present simultaneous with their expression (complex tones); that's just the way the human ear works.
 
.....But add a little distortion—a very little distortion—to the sound of a full orchestra going full-tilt' date=' and see what happens. Intermodulation produces sum-and-difference tones, most of which are not harmonically related to the fundamentals. The result is what the ear interprets as dissonance. The sound becomes irritating. Harmonic distortion adds new overtones that were not there originally. The sound becomes brighter and "hotter."[/quote']
 
No support for this, just opinion.  What about the observer that states "I have a low level hum during quiet passages, but everything's fine when music is playing"  Is he also a clown?  Why doesn't he hear this inharmonic distortion during music passages?  The most likely case, given the known characteristics of auditory masking,  is that the hum is being masked.
 
Similarly, it can't be rightfully concluded that the high level of distortion the panel tolerated was due to the music's harmonic relation to the distortion.
 
Holt seems to be talking about harmonic and non harmonic distortions as being either pleasant (tending to blend in) or dissonant.  This ignores the fact, for example, that all push-pull type amplifiers, solid state or tube, cancel even order harmonics; that's just by nature of the push-pull design.  The opinion that a tube amplifier is perceived as 'warm' due to its harmonic nature is not borne out by fact.
 
.....Mix in a typical amount of disc mistracking distortion' date=' and the high-frequency breakup energy intermodulates against the program frequencies and splatters the distortion all the way down through the range below it.[/quote']
 
unsupported techno-babble 
 
I couldn't agree more. Stereophile is populated (IMHO) by a bunch of narcissistic, nihilistic nincompoops who obviously have more money than common sense and more  %*(t  than a Christmas goose. (Contrary to popular belief, I am not - nor have I ever been - Spiro Agnew's speechwriter. Moving on...)  Bob and the Golden Ears have always had it right, because the human ear is by its very nature a flawed instrument that cannot be calibrated to a set constant from one pair to another...only a 'range' can be quantified. It is for each individual to find the combination of ingredients that satisfies them alone, and not cleave unto some over-inflated twit who lives for braggadoccio over musicality.
 
That being a given, and noting that all non-scientifically-supported opinions are by their very nature objective, what Bob has always supported makes superlative sense.  Audio enjoyment is by ITS very nature subjective - else we'd all be listening to the same music (music?) the same way from the same source. That's what drives industry and makes us all happy campers. Snobs like JGH and the rest of the 'tweako' groups like Stereophile are only about the 'bling' and not about real music enjoyment.
 
'Bang for the buck' is just another statement to be blown out of proportion by these gentle people. To me, accuracy in reproduction is of paramount esoteric importance, secondary to the ...oh, what is that....oh yeah, MUSIC...itself. 
 
Most of us (I'd think) don't live in a concert hall or even close to it, so we'll take a full measure of accuracy with a bit of detail thrown in, if you please. Why must it be delineated as 'harsh', 'shrill' or whatever when you hear the crash of a cymbal that, for a nanosecond, drowns the snare drum? Isn't that the way it sounded in the first place? 
 
Finally, before I get off my own soapbox, why don't we use a more accurate, less self-centered term for those like us, and go with "Hi-Fi enthusiasts"? It's not only more accurate, it's less indicative of the snobbery which JGH and the Stereophile-types love to promulgate to their own profit.
 
...And all this from a 52-y/o former Airman who lived around jet engines most of his adult life. Can't hear my wife calling for me, but I still thrill to  hearing things like the sound of the sliding guitar fret change in the beginning of Heart's "Crazy On You", et cetera.
 
'Kay. I won't say any more.  I just get riled up hearing stupid people spout b.s. like that. Sorry. I'll go back to my corner now...
 
 

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