herman, I agree on final sound check of any audio component in sound system, to make sure if no hum noise, microphonic effect (rubber hammer tap test), etc.
the problem is in using “listener" as sound quality assessment, because all humans are not reliable in terms of repeatable sound grading, if they can’t see which unit is put under test. using human ears and brain is the biggest variable in ranking sound, because “listening” is biased by reviews, optical appearance, friend’s opinion, etc. just ask someone to connect different units, presumably with matched signal level etc., and listen the sound without knowing what is playing. repeat the same after cup of coffee, taking break etc.
the problem is in using “listener" as sound quality assessment, because all humans are not reliable in terms of repeatable sound grading, if they can’t see which unit is put under test. using human ears and brain is the biggest variable in ranking sound, because “listening” is biased by reviews, optical appearance, friend’s opinion, etc. just ask someone to connect different units, presumably with matched signal level etc., and listen the sound without knowing what is playing. repeat the same after cup of coffee, taking break etc.