On measurements. I have pointed out to Raul many times that if THD had so much "meaning" in relation to lowering audible distortions in our audio system, then amplifier development might have ceased back in the 70s, with the advent of the Phase Linear 700 amplifier. THD was at least down to the 5th decimal place. It sounded like crap compared to any modern amplifier and compared to any quality tube amplifier, ever. So, THD needs to be thrown out as a yardstick. Even manufacturers of solid state amplifiers, which can easily show superiority to tube amps by this meaningless parameter, downplay it these days. Yes, there is probably some high percentage of THD that would be audible, but it would be difficult to establish the cut-off. Harmonics are not all that disturbing to the brain.
Now, as to wow and flutter. I have no idea how much is too much.
Now, as to wow and flutter. I have no idea how much is too much.