I don't want to beat a dead horse but I'm bugged.

Amir is a good resource as an alternative viewpoint. His ‘truth’ is a series of measurements, that can tell a lot about how some components will perform. But he does miss some of the picture no doubt. A couple of his component reviews are way off the mark. Maybe a faulty product? Or his measuring system at fault? Who knows? Take Audio Science Review for entertainment value, and some worthwhile information.

The problem was not Amir himself but few of his zealots disciples...

Because the notion of a measured distortion in engineering design is not the same than in acoustic...

Why ? Because acoustician test a subjective response from a musician for example in a timbre experiment perception test...harmonics here means something very different than " harmonics" in engineering standard measures...

And the engineer read a dial and his "distortion" THD is a way more simplistic concept of what a distortion do to the subjective impressions and why....It is an engineering % about a relation between input and ouput...Not the way sound affect humans ears...

Electronic Engineering is SUBORDINATED to psycho-acoustic research or a tool for it not the reverse ... Save when the psycho-acoustic research is done and applied....

Timbre perception is not reducible to a simplistic concept of the spectrum for example....but the engineer most of the times work with this simplistic concept which is well enough for his design trade-off  practice anway ... There is exception but they are exceptional designer not a crowd of them ...All audio products are not ultra high end... 😁😊

Atmasphere has numerous posts about amplifier harmonic distortion and listener perception. Simply stated, vanishingly low harmonic distortion is not necessary. The harmonic spectrum and linearity of the distortion are more important. So whether THD is .001% or a hundred times greater is pretty irrelevant. Clearly measurements matter, it’s just that the most commonly cited amplifier measurements aren’t the most important regarding sound quality.

Exactly....Some designer like atmasphere know....

It seems many amplifiers have lots of negative feedback and they have low distortion at 20Khz.

I don't think it is back in the day any more. There are lots of amplifiers on Stereophile and ASR that have very low distortion at 20Khz. Lower than this Rogue at almost any frequency.

It needs to be more than just low distortion at 20KHz although that certainly does not hurt. What is important is four things; if these four things are met, the amp will be easy to listen to, regardless of its technology:

1) the distortion will be consistent at all frequencies- the same at 100Hz, 1KHz and 10KHz.

2) the distortion spectra at 1 Watt will be such that the higher ordered harmonics will not be audible- for whatever reason.

3) The distortion spectra at 6dB below full power will also prevent higher ordered harmonics being audible.

4) IMD is well controlled.

These things sound simple and easy but they can be quite tricky! Most amps fail them outright- and sound bright and harsh as a result, even though they 'measure well' otherwise. The real problem isn't that they measure well, its that the proper measurements aren't made at all!

Many amplifiers on tested on Stereophile and ASR meet those criteria @atmasphere .  By low, I don't mean only low at 20KHz, but low at all frequencies, <<0.01% at all frequencies. I don't think distortion has any particular meaning at >10KHz as the distortion is >20KHz. I assume the measurements are using an extended bandwidth beyond human hearing.  ASR shows distortion from low to high power at a range of frequencies in their reviews.

@atmasphere 

Most amps fail them outright- and sound bright and harsh as a result, even though they ’measure well’ otherwise. The real problem isn’t that they measure well, its that the proper measurements aren’t made at all!

The absolute truth in my opinion. Current test bench measurements are inadequate. It makes no sense to measure good and yet sound poorly. What good are measurements such as these?

There are numerous audio components that don’t measure particularly well yet sound fabulous. Ralph is correct in that what really matters in determining good sound quality is not being done currently with measuring instruments. I do believe at some future point this dilemma will be properly solved. It sure is not the case now.

I guess for some there’s a degree of reassurance or peace of mind with current methods of audio component bench testing. As it stands presently the ears are far more reliable and trustworthy in judging audio product sound quality.

Charles

I assume the measurements are using an extended bandwidth beyond human hearing.

The problem if i may give my grain of salt, is that we dont exactly know what are human hearing abilities...

Human hearing limit in decibel scale and in the frequency scale yes we know but what about the way the brain/ears used the information and decipher it with the non linear tool kit of the cochlea/brain ?

In the words of these mathematical physicists turned acoustician:

Jacob N. Oppenheim and Marcelo Magnasco of the Laboratory of Mathematical Physics at Rockefeller University have conducted experiments indicating that the human brain does not use the Fourier transform when resolving a cacophony of noise into individual sounds and voices.

While the Gabor limit associated with the Fourier transform stipulates that you can't simultaneously determine a sound's frequency and duration, the 12 musicians subjected to Oppenheim and Magnasco's battery of tests beat the limit by as much as a factor of 13.

The Fourier transform cannot, therefore, fully explain the machinations of the human brain. "The actual algorithm employed by our brains is still shrouded in mystery," says Magnasco.

«You see, physicists tend to think hearing is spectrum. But spectrum is time-independent, and hearing is about rapid transients. We were just told, by the data, that our brains care a great deal about timing.»

«For the first time, physicists have found that humans can discriminate a sound’s frequency (related to a note’s pitch) and timing (whether a note comes before or after another note) more than 10 times better than the limit imposed by the Fourier uncertainty principle.»

«

The results have implications for how we understand the way that the brain processes sound, a question that has interested scientists for a long time. In the early 1970s, scientists found hints that human hearing could violate the uncertainty principle, but the scientific understanding and technical capabilities were not advanced enough to enable a thorough investigation. As a result, most of today’s sound analysis models are based on old theories that may now be revisited in order to capture the precision of human hearing.»

This article is particularly illuminating if someone take the time to read it and his imnplication to understand hearing and why our measurements are not the good one...