From the article, "Maybe the golden ears at the tweak magazines have really been hearing something all along—they just couldn’t identify it or measure it. Maybe this is it."- But that didn't stop them form using words that bore no resemblance to the differences they heard.
In the '70s, the magazines ran tests of amplifiers with square wave and the ones that didn't overshoot usually had some amount of ringing. Sometimes, it was symmetrical, sometimes it wasn't. Harmon Kardon and Sansui touted their Direct-Coupled designs and Sansui especially, let everyone know their amps had a higher slew rate than many others. Consumer Reports loved both brands, but they didn't see how many of these receivers came in for service, either. The Sansui R-series were so bad that one of our service techs quipped "They put the output transistors in to protect the fuses".
Anyone who remembers Len Feldman also remembers that he was seen as an expert. He was one of the members of the "All amps that are running in their normal operating range sound alike" and then, somehow, he changed his tune. I don't remember who or what made him change, but he was adamant about this and those of us from the stereo shop where we worked discussed this with him at an event where he was featured.
I didn't go to school for electronics, but I have learned a lot in the last 40+ years of working with this equipment. While I have always been able to hear details, I have never been so neurotic about the sound that I was willing to spend all of my money in an attempt to have "the best" and often tell people to "listen to the music, not the equipment".
Having many friends who are electrical/electronic engineers has been a real benefit and the discussions we have had were extremely informative for me. Part of my interest has to do with old tube guitar amps and one thing that I have learned is that it's possible to make some small changes and it WILL be audible. From changing the output devices, filter caps, component tolerances and power supply configuration to the amount of NFB or lead dress, it's audible. Sometimes, an amp will oscillate when it isn't expected, but not hard to cause. Sometimes, all of the best intent brings harshness or grit to the sound. Sometimes, it's just a matter of using better outputs that work in the same configuration as the original ones or changing the bias. I just bought a Parasound amp and in some YouTube videos, John Curl talks about eliminating the 7th harmonic. I haven't seen the square wave response, but I would assume it's pretty good. I don't hear an edgy sound but I do hear details and dynamics I never did with the Denon AVR I was using.
FWIW.
