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In Reply to: RE: Listen for yourself posted by Donald North on July 07, 2017 at 10:39:56
Perhaps I should expand upon my previous response to your posting.I apologise if I picked the wrong word by describing the sound from an SET amplifier as "pleasing," since it might perhaps have carried a connotation of condescension that was not intended. I was just looking for a word that conveyed the idea that the sound gave a more satisfying all-round experience for the listener. And in that sense, I would describe a system that "had more instrument texture, nuance, natural clarity and presence than anything I heard heard to date" as a system that had a more "pleasing" sound. Perhaps there is a better word I could have used.
Now, as regards my statement that I suspect that these phenomena can be accounted for in terms of rationally understandable scientific principles, let me expand a little on this. Of course, ultimately, one (or at least a scientist such as myself) would wish to be able to explain everything we observe in terms of the most fundamental concepts and building blocks (quarks, leptons, strings,...????), but obviously at present that is not feasible. But explanations of phenomena in terms of more general observed phenomena can also be perfectly "scientific," even if they do not go all the way back to the level of the fundamental building blocks.
In the present context, I would take the observed psycho-acoustical characteristics of the human mind and ear as scientific phenomenological observations. A couple of examples are:
1) Humans find mixtures of frequencies that are related by simple rational ratios to be pleasing to the ear, and on the other hand irrationally-related mixed frequencies tend to sound unpleasant. Based on this observation, one can predict that if one made a sound-producing system in which all frequencies were shifted upwards or downwards by a constant additive amount, then music played through this system would sound absolutely dreadful. And this is, I believe, borne out by experimental observations. (A simple way to test this is if one has a shortwave receiver with narrow-band filtering that can block the central carrier frequency, and one then replaces this with a local BFO operating at a slightly different frequency.)
2) Humans find that the addition of the second harmonic to a tone or set of tones can provide a pleasing (in my generic sense) alteration to the overall effect. In particular, in a piece of music it can lead to an augmentation of the feeling of "liveliness," and maybe it can allow the brain to interpolate or extrapolate and give more of a lifelike overall experience. (Research in psycho-acoustical phenomena, as with many other aspects of the interaction of the brain with our exterior senses, seems to indicate that the brain does an amazing job of "filling in" the things that are inadequately conveyed to it by our sense organs.)
As a rather trivial hypothetical example, if it were the case that broadcast music stations used single or double-sideband AM transmissions where the carrier was removed and needed to be restored in the end-user's receiver, then one could easily make a general "scientific" observation that the best-sounding receivers would be those that restored the correct suppressed carrier frequency, rather than one that was displaced up or down by some amount. This would not be in the least bit controversial.
In a similar vein, it is a perfectly legitimate scientific endeavour to look for what characteristics of an SET amplifier might be responsible for giving humans the feeling that the performance is more "alive," or have more instrument texture, nuance and clarity. It seems reasonable to suspect that the phenomenological observations noted in point (2) above could be playing an important role, especially when one notes that one of the most striking distinguishing features of an SET amplifier is the relatively large percentage of second-order harmonic distortion.
Thus, I don't see why there should be anything controversial about the suggestion that if one can identify certain generic and measurable characteristics of SET amplifiers that distinguish them from most other amplifiers, then it is quite likely that it is these characteristics that are playing an important role in accounting for why they produce the audible sensations ("presence," "nuance," "instrument texture," or whatever) that they do. Thus, technical measurements of an amplifier's distortion and other characteristics (such as frequency response) might very well allow one to predict what kinds of overall impression it could give to the listener. You may be right that there are further characteristics of an SET amplifier that have yet to be identified and measured, but I wonder if there is really solid evidence for this?
Chris
Edits: 07/07/17Follow Ups:
You say again "one of the most striking distinguishing features of an SET amplifier is the relatively large percentage of second-order harmonic distortion." As I previously said, I have made SET phono stages and headphone amplifiers which have very low measured distortion in their normal operating range yet they still sound different and I believe superior. I don't believe this is attributable to 2nd harmonic distortion when the THD is less than 0.1%. Another differentiating factor which you have not mentioned is the fact that they do not split or mirror the phase as do differential and push-pull amplifiers do. I believe this is a contributing factor to the SET sound.
An example: Back in the 90s Audio Note UK made two tube amplifiers that were as identical as possible, one a parallel single ended, the other a push-pull. The reviews all said the single ended version sounded better.
"I have made SET phono stages and headphone amplifiers which have very low measured distortion in their normal operating range yet they still sound different and I believe superior. I don't believe this is attributable to 2nd harmonic distortion when the THD is less than 0.1%"
I think simple SE amplifiers made with direct heated triode output tubes that do not use feedback are notable by what is lacking in the HD. Namely, upper order HD.
I believe it's not the (relatively) high amounts of 2nd HD that make them "sound so good", it's the lack of 5th, 7th and 9th.
I believe (but can not prove) that the smallest amount (maybe even an amount that can't be measured) of 7th and it's game over. The electronics sound like electronics instead of music.
I could be proven wrong on all counts but this is what I believe and it is what guides me when designing circuits and picking operating points.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
and Crowhurst even fought for a weighting system which would have assigned higher penalties for 5,7, and 9. There is text somewhere on the net about him and some BBC guys advocating for this but were shouted down by manufacturers. and they specifically mentioned upper odd harmonics at some crazy low levels being very annoying.
Yes and these were serious proposals.One would be multiplying the percentage measured by the order. 5th would be the measured % times 5. 7th would be the measured % times 7.
The other proposed method would have been the % measured times the square of the order. 5th would be the measured % times 25 and 7th would be the measured % times 49.
These proposals were intended to better reflect the annoyance factor.
THD doesn't tell us much in terms of the annoyance factor. We need to now the orders of the HD.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 07/07/17
"and Crowhurst even fought for a weighting system which would have assigned higher penalties for 5,7, and 9. There is text somewhere on the net about him and some BBC guys advocating for this but were shouted down by manufacturers. and they specifically mentioned upper odd harmonics at some crazy low levels being very annoying."I agree that that is a very interesting point, and maybe is highly relevant. Do you, as a matter of interest, know if SET amplifiers tend to have lower odd-harmonic distortions than PP amplifiers? I just don't know one way or the other; I don't recall ever having seen studies of this question.
In any case, such things should lie within the threshold of measurability, presumably, and so they would be part of the whole package of "measurements that can be correlated with observation" in the spirit of the scientific method.
Chris
Edits: 07/07/17
"I believe it's not the (relatively) high amounts of 2nd HD that make them "sound so good", it's the lack of 5th, 7th and 9th.I believe (but can not prove) that the smallest amount (maybe even an amount that can't be measured) of 7th and it's game over. The electronics sound like electronics instead of music."
You may be right that it is a lack of higher odd-harmonic distortions that is responsible. (Is this actually a property of an SET, by the way? I can see why it would tend to have more even-harmonic distortion than a PP amplifier, but is there a reason why it would have less higher odd-harmonic distortion? I'm not doubting, just asking.)
However, what about the suggestion that the higher odd-harmonics below the threshold of measurability, could be responsible? A modern state-of-the-art spectrum analyser is amazingly sensitive. Is there really any reason to suspect that amounts below the threshold could have audible effects? Or is this an example of the very human desire (in some humans at least) to believe that there are things that lie beyond our understanding? If it could be demonstrated in convincing experiments that such effects were occurring, I would be only too happy to accept them. But I wonder what evidence there might be?
As a matter of practicality, I would have thought that any real-world amplifier in existence today would have 5, 7 and 9th order distortions that are actually within the range of measurability by present-day spectrum analysers, and so speculation about the possibility of such distortions below the measurable threshold would be, at this stage at least, academic. (Again, if I am wrong about this, I would be happy to be corrected.)
Chris
Edits: 07/07/17
Chris
It has been noted that the use of negative feedback can reduce second harmonic distortion, however Dr. Earl Geddes (among others) has noted that added second harmonic distortion is relatively difficult to hear compared to other types of distortion. The second harmonic is an octave above the fundamental and harmonizes with the fundamental which makes it difficult to separate in our perception from the fundamental. While negative feedback reduces the second harmonic, it can actually increase higher odd order harmonic distortion. As the second harmonic is the biggest number, reducing it makes the total harmonic distortion number look better at the expense of increasing higher order odd harmonic content which has been shown to be perceived as unmusical. But you don't have to believe me on this, Jean Hiraga wrote several articles examining this subject going back into the late 70's and 80's which we didn't get here in the US unfortunately until the oughties when they were reprinted in AudioXpress. See the link here for the Amplifier Musicality article which was followed by rebuttals from two experts, and which was followed by a rebuttal by Hiraga with no rebuttal to Hiraga's rebuttal.
Paul
I'm pressed for time right now but a DHT is very linear. If loaded and driven correctly, and without NFB, there is not much of a mechanism for producing upper ordered HD."Norman Crowhurst wrote a fascinating analysis of feedback multiplying the order of harmonics, which has been reprinted in Glass Audio, Vol 7-6, pp. 20 through 30. Mr. Crowhurst starts with one tube generating only 2nd harmonic, adds a second tube in series (resulting in 2nd, 3rd, and 4th), and then makes the whole thing push-pull (resulting in 3rd, 5th, 7th, and 9th), and last but not least, adds feedback to the circuit, which creates a series of harmonics out to the 81st. All of this complexity arises from theoretically-perfect tubes that only create pure 2nd harmonics!"
__
I believe there are studies showing that humans can hear well down into the noise floor.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 07/07/17 07/08/17
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