In Tape Op #86, Greg Calbi related his early experiences as a mastering engineer. I was struck by his comment that professional mix engineers would ask him if a bass or vocal was too loud or too soft. Greg explained that what sounds right or wrong when making such decisions is "fluid." Chick Corea expressed a similar opinion in a recent Keyboard Magazine interview, stating that artistic judgment varies from one moment to the next. Everyone has experienced creating a mix that sounds stellar at the time, only to realize the next day that it actually sounds like crap. The frailty of auditory perception affects both amateurs and professionals alike.
Hearing fallibility has implications beyond doubting our own mixing decisions. It's the main reason audiophiles believe the sound of their hi-fis improves after replacing one perfectly competent AC power cord with another, or after raising their speaker wires off the floor on special "anti-resonance" cable lifters. Understand that I'm not talking about real differences, such as the sound of modern digital recording versus analog tape or vinyl records. Those differences are real, and are easily measured using the standard metrics of frequency response and distortion. Skilled listeners can easily identify which is which, nearly every time, in a blind test. Rather, what I'm addressing are differences that are perceived but not real — the placebo effect, if you will, or perhaps wishful thinking.