This is the measurement. The noise of the op-amps matches the datasheet spec. I haven't listened to these amplifiers. They were used for measuring purposes only. This gives me an idea to connect a pair of headphones and to take a listen. 
BTW - the schematic used to measure the spectrum above is attached.
BTW - the schematic used to measure the spectrum above is attached.
Attachments
LEMEXBBE,
Some of us have different experiences. IME a little more low level THD only helps when the reproduction system is compromised somewhere in the chain. Then a tiny of bit of THD can give a false impression of improved clarity. In other words, the THD helps cut through something in the way of a muddy sound that shouldn't be that like that in the first place. IMHO and IME only, of course
Some of us have different experiences. IME a little more low level THD only helps when the reproduction system is compromised somewhere in the chain. Then a tiny of bit of THD can give a false impression of improved clarity. In other words, the THD helps cut through something in the way of a muddy sound that shouldn't be that like that in the first place. IMHO and IME only, of course
Have to agree sometimes we tend to focus on the numbers more than on the sound. Is that what they call, "listening with your eyes?"
It's a crying shame that there is still a significant proportion of the human race who are still deluded enough to think that the quality of a piece of audio equipment should be deduced by listening rather than by rigorous technical and scientific measurements -- a crying shame!
I think you are making it up: no one, as far as I am aware, has ever claimed that "AP measurements completely predict sound quality". The purpose of all measurement tools is to help the designer to eliminate or minimise error.
It is folly and monumental ignorance for one to suggest, for example, that one can hear the difference between two or more amplifiers producing, say, 100 Watts into eight Ohms at less than 100 parts per million THD plus noise across the audio band. This is complete folly.
It is folly and monumental ignorance for one to suggest, for example, that one can hear the difference between two or more amplifiers producing, say, 100 Watts into eight Ohms at less than 100 parts per million THD plus noise across the audio band. This is complete folly.
Guilty as charged. In my defense, even though superficially educated i am also in possession of a pair of obstinate and insolent ears that flatly refuse to understand arguments and common sense. Should i send them off to a re-education camp?
No disagreement that measurements should be reasonably used to help find problems. However when it comes to design for audio, IMHO listening tests have a significant place too. In my view foregoing either type of testing would be unwise. If a trade off between measurement goals and listening test goals is found to be necessary, my personal preference would be to favor the listening tests.
In addition, by listening tests I don't necessarily mean double-blind ABX. Those are fine, but not always necessary when differences are easily audible to multiple independent listeners who are not aware of each other's listening results. Particularly so when the listening is for discrimination tests rather than for preference testing.
In addition, by listening tests I don't necessarily mean double-blind ABX. Those are fine, but not always necessary when differences are easily audible to multiple independent listeners who are not aware of each other's listening results. Particularly so when the listening is for discrimination tests rather than for preference testing.
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We hear acoustic output, measurement into an 8 ohm resistor produce no acoustic output, pretty much useless.It is folly and monumental ignorance for one to suggest, for example, that one can hear the difference between two or more amplifiers producing, say, 100 Watts into eight Ohms at less than 100 parts per million THD plus noise across the audio band. This is complete folly.
There are a few people that have the skill to reliably recognize audio systems by their sound. One such person was described and vouched for here at diyaudio by a professional listening perception researcher who was otherwise convinced that everything people hear is at some level delusional. The guy who could recognize systems by listening alone also happened to be blind. In that sense, all of his listening was blind listening.
We hear acoustic output, measurement into an 8 ohm resistor produce no acoustic output, pretty much useless.
Such ignorance!
Yeah, now THAT guy I can believe could hear the difference between audio devices! After all, all his brain power that was once divided between sight and sound is now tuned focused totally on sound. HOWEVER, he still can't tell you which system sounds better to YOU---only YOUR ears can do that.
Such ignorance!
Worldie, that is over the line and you know it.
I'm firmly in the measurement camp myself, but I don't pretend that THD+N vs frequency and voltage comes remotely close to telling the whole story of a signal path.
I do believe that if an audible difference can be heard, then there has to be a measurement that will correlate with that. Is it relative harmonic levels, IMD TIM, damping factor, slew rate, headroom, or something else? A lot of the silly measurements of the past, such as TIM-100K, were born out of a desire to find measurements that correlated to what was heard. Sometimes these were successful, sometimes not. Sometimes, a desired sound correlates to a spec that is actually worse. Subjective results are like that. Some people like sweet things and some like bitter. Some people really like the sound of their systems with 10% THD, because it's louder.
I personally believe that THD should be as low as possible and dominated by the 2nd harmonic. Harmonics above the 4th should be below the noise floor. Noise should be a low number on a spec sheet and inaudible. Slew rate spec should be >10x what the signal requires. If you like a system that scores poorly on these metrics, then I am not designing for you.
I do not discount what people say they hear, until they are proven wrong in blind A/B testing. I may ask them to help me hear it, too, so I can design the correct test for that problem.