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Old 1st November 2012, 08:39 PM   #131
Merlinb is online now Merlinb  United Kingdom
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Quote:
Originally Posted by Shoog View Post
Its a dangerous place to be when you are prepared to stand against everyone in expressing a theoretical position over their personal experience.
It is OK to state your personal experiences of listening to equipment, but it is dangerous to attribute your various subjective experiences to highly technical issues like 'feedback in general', especially if you do not understand those technical issues at a high enough level.

The subject of feedback is so broad and intricate, that it is exceedingly difficult to make a fair test that can truly identify feedback as being the cause of the 'niceness' (or 'badness'!) of a listening experience.

You might think it would be a simple matter of building an amp, and then adding some variable feedback, and listening to it while varying the feedback. But is that a fair test? By adding feedback you're altering the transfer curve and moving the poles around, so really you're comparing two very different amps. Apples with oranges. Keep adding feedback and you may border on instability. Is that the feedback's 'fault'? No, it is the designer's fault.

A fairer test might be to build two amplifiers, one with feedback, one without, but arrange both circuits to have the same transfer curve and the same poles/zeros.
This is not an easy test to carry out, and until someone does, it is very bad science simply to brand gNFB as 'bad for music' and bury your head in the sand thereafter.
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Old 1st November 2012, 09:08 PM   #132
Bigun is offline Bigun  Canada
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Originally Posted by DF96 View Post
I don't trust my own ears
If you are designing and building for other people then fair enough, but if it's DIY and you don't trust your own ears - what's the point of it ?
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"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.
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Old 1st November 2012, 10:01 PM   #133
DF96 is offline DF96  England
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The point is listening to music, with my amplifier doing as little as reasonably possible apart from amplifying the signal. If I make a change and it sounds better/worse, then I need to convince myself from science that it really is better/worse and not the reverse.

Lets say I make a change and it sounds better. Then I find by some combination of measurement or calculation that it is actually worse (e.g. higher distortion, less flat frequency response). I therefore conclude that my ears are deceiving me. I do not conclude that my change has introduced some unmeasured/unmeasurable advantage.

Sometimes my ears and calculations tell me the same thing, such as when I found I had miscalculated the deemphasis capacitor for my FM tuner. I tried different caps, then afterwards found that the one which sounded 'right' happened to calculate right too. I don't assume this happy coincidence will always happen. The only reason I did this 'tuning by ear' was that I knew I could calculate the right value and I was curious to see how much audible change the wrong cap did.

Last edited by DF96; 1st November 2012 at 10:02 PM. Reason: typo
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Old 1st November 2012, 10:05 PM   #134
Hierfi is offline Hierfi  Canada
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Originally Posted by SY View Post
There are thousands who disagree with me about alien abductions and the existence of fairies. So what? Data are everything. No data, you're just waving your hands.
I first became aware of an alien presence when my parents revealed themselves to me. As it was explained, only fairies passing themselves off as aliens were engaged in the alien abductions being alleged and misreported.

I have always treated dielectric materials as critical. To be brief, dielectric absorptions are occurring when electrons move in and out of materials in depth. This is a function of voltage and released in delayed time. Under conditions of a sine wave being imposed this can create delayed sine wave fundamental reflections being released.

This suggests that the nature of dielectric effects can be created by imposed a sinusoidal signal by a distortion analyzer. What I am trying to suggest is that the fundamental frequency being treated as pure and clean in a distortion analyzer cannot be taken as true. The fundamental frequency can also contains artifacts of sinusoidal dielectric effects buried within the fundamental. Being phase shifted doesn't change the fundamental frequency.

If one is going to emphasize the worth of a device by the distortion measurements the question I would have is to what degree the fundamental is a true reference to distortions, those that could be greater and hidden within the fundamental itself. It isn't clear to me the quantitative differences ,nor the degree, of harmonics vs. dielectrics.
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Old 1st November 2012, 10:10 PM   #135
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If all this was just a personal experience then I wouldn't make any fuss over it - but its a very general observation that I am commenting on, shared with some of the best and most respected designers on the planet. I think I am justified in drawing some broad general conclusions about the effects of the application of gNFB, and not just take our "experts" word for it.

Shoog
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Old 1st November 2012, 10:18 PM   #136
DF96 is offline DF96  England
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Quote:
Originally Posted by Shoog
shared with some of the best and most respected designers on the planet.
Is this a fact or an opinion? I have sometimes seen the 'most respected' people talk nonsense, and sometimes talk wisdom. In either case, the test is not "who said it?" but "is it true?".
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Old 1st November 2012, 10:22 PM   #137
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Lynn Olsen, Allen Wright, Gary Pimm and Nelson Pass. I would take any one of their opinions over yours DF96.

Shoog

Last edited by Shoog; 1st November 2012 at 10:26 PM.
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Old 1st November 2012, 10:34 PM   #138
DF96 is offline DF96  England
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Yes, you have already made that clear. It is up to you whose opinions you accept.
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Old 1st November 2012, 10:42 PM   #139
Merlinb is online now Merlinb  United Kingdom
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Originally Posted by Shoog View Post
Lynn Olsen, Allen Wright, Gary Pimm and Nelson Pass. I would take any one of their opinions over yours DF96.

Shoog
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Old 2nd November 2012, 03:39 AM   #140
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I hesitate to comment on the 'many people agreeing with me' kind of argument. Yes, it probably is true - but has a poll ever been taken? OK, before folks me for becoming ridiculous/hair-splitting .... but isn't the truth that as many disagree? ... meaning that one probably tends to remember the favourable better than the opposite. All in all, I would certainly not venture to take such statements for unequivocally establishing what is true and what not. Leaving that for the moment - because truthfully Shoog said that it has the danger of steering toward escalation.

Rather: I am not any great audio engineer (certainly not in terms of being well-known), but I would challenge certain statements on grounds of what is revealed (our friendly internet) by probably acceptable tests done under as controlled conditions as one could wish for, including statisticaaly valid conclusions. One is that there are audible things out there that science still cannot measure. Sorry; it would appear that present technology is up to detection comfortably deeper than audible discernment. Again, with full respect for disagree-ers: Science is not democratic. (I sometimes wished it was, but having spent my professional life in research, that convenience was never an option.)

Then, I would agree that simply applying nfb in varying amounts per se and using the audible results as gospel, cannot float as such. (By the way, nobody said thd is an acceptable measure of anything; well, I certainly do not.) I have analyses on a modest amplifier that I designed showing that up to 30dB of global nfb reduces higher order harmonics up the no. 11 by almost equal quantities. But, on the way there I also found that there are ways of using nfb that started 'backfiring' after some 13 dB - as witnessed to previously. (It depended on the topology; not having maximum linearity to begin with, very easily gave that result.)

I must concede that these tests were for a power amplifier; I do not have the equipment to measure in the 0,00x% required for pre-amps. Still, I do believe that the tendency holds.

Then, I still read about how the result sounded. What did the original sound like? Proper amplifier measurements regard the addition of anything by the amplifier, not the end result per se. (In that respect such yardsticks are often simpler than obtaining a final "niceness" experience.)

Finally, and certainly without any intention to offend: When last did you have your ears tested? (Not necessarily asked of honourable members posting here ). Still, that question is relevant, at least for some people proclaiming their experiences of niceness! As said before, any test that does not exclude taste can be questioned.
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