Negative feedback Amp=more faithful reproduction?

Negative feedback reduces harmonic and intermodulation distortions, reduces output impedance and widens bandwidth. This can be easily measured. Negative feedback, especially a global one, can introduce Transient Intermodulation Distortion (discovered in 70's) that enhances odd order harmonics making sound bright and unpleasant. Loudness cues are in these harmonics and our ears are very sensitive to them. Transient Intermodulation can be completely avoided if bandwidth of the signal is limited at the input of the amplifier to value that amplifier had without feedback. For instance, if measured bandwidth is 30kHz without feedback then it has to be input limited to 30kHz after feedback is applied (that increased amps bandwidth). It is harder to design an amp that measures good with shallow feedback and often designer chooses to improve specifications at the cost of the sound. I would start width the best widest bandwidth most linear design and apply only enough feedback to reduce THD to 0.1%. After that I would temporarily disconnect feedback and measure bandwidth with very small signal. Finally I would limit bandwidth at the very input of the amp to this amount.
It is a tradeoff between THD, IMD and the bandwidth. If you want to lower THD, IMD by use of feedback then you need more gain and amp has lower bandwidth at the higher gain. Bandwidth will increase greatly with feedback but not limiting it at the input to original one will enable TIM.

Transient Intermodulation is practically an overshoot (in time domain) caused by the fact that amplifier, having limited bandwidth, introduces signal delay. This delayed signal is subtracted at the input reducing gain of the amplifier. For instance 40dB negative feedback means that amplifier has 100 times bigger gain without the feedback. Feedback lowers this gain to normal except for the moment of fast transition of the signal because feedback signal is subtracted a moment too late (being delayed) and amplifier has for this short moment 100x higher gain. It causes overshoot of transitions (enhanced odd harmonics) but doesn't show at sinewaves, normally used to test THD and IMD.

""You compared the input signal to the output signal." Just how simplistic is this? So, I'll make this easy..."

Oh no you didn't. You didn't just try to dis me? ;) I don't think you are being condescending, so I'll give you benefit of the doubt and assume you are asking a genuine question. If that is the case, I thank you for your response.

"...if the two signals are exactly the same but one has 3% second harmonic distortion, and the other has .8% of the, more jarring, 7th harmonic distortion, which is the more "faithful"? Please answer my question."

Sure I'll answer. The result is the result and can't be disputed assuming you measured it correctly. What you're talking about is the INTERPRETATION of the result, which can be disputed. I do not know how a 3% 2nd harmonic distortion sounds relative to a 0.8% 7th harmonic distortion. But if the 7th harmonic distortion is say 80 dB down, I doubt I could ever hear it. Now 3% 2nd harmonic distortion may be audible, so I would consider that less faithful reproduction than a "jarring" 7th harmonic distortion I can't hear. Your interpretation may be entirely different than mine.

I can see how some might consider my input/output comparison simplistic. So let me explain. Why is it that a square wave is one of the industry standard of measurement of how an amplifier performs? Music does not contain square waves as far as I know. And I doubt if anyone considers a square wave a close facsimile of a music signal, which what an amplifier is suppose to reproduce. Wouldn't a more appropriate test signal be that of an instrument at certain frequency (eg, 1 kHz piano, guitar, or sax tone). Or even an instance of music containing many instruments. Is this technically too difficult to perform? I am relatively new at looking into the technical side of amplifier circuitry and performance, so my questions may seem naive to those who have years of technical experience. But this is one of the reasons why I started this thread. I would appreciate input from experienced individuals who would take the effort to be informative. As in any controversial thread, there will be individuals who will have nothing better to add other than dumb sarcastic or condescending comments.

Hi Kijanki, thanks for your input. What do you think about the article I linked?

Hi Elizabeth, what is a current fad or "catchphrase" is not important to me, but the finding the underlying reason for "catchphrase" or current fad is. If I did't think NFB or ZNFB made a difference in sound, I wouldn't have made this inquiry.

Elizabeth, I have and owned amps that have adjustable NFB, and you can clearly hear a difference between different levels of feedback. IME, the higher feedback setting produced more realistic sound. So your contention feedback has little to do with how a product sounds is in direct contradiction to my experience. Do you have any amps with adjustable feedback? If you do, I would be surprised if you can't hear a difference.