Mood and environment are important factors to consider when evaluating equipment designed to elicits emotional responses. You wouldn't want to judge how something makes you feel when you're feeling off. It skews the test. And this reminds us that we are not machines with identical responses to external stimuli.
If the environment is wrong, that too skews the test, like evaluating differences in stereo equipment on inadequate or unfamiliar equipment, tension created through rigorous testing procedures, or pressure to make a decision. These factors all play in to our ability to make judgments because we are not meters or electromechanical devices that act the same on any given moment.
When I need to make an informed decision between two pieces of gear, or two types of firmware, or compare any two variables on the stereo system, here's what I do when decisions aren't obvious. Making sure there are no volume differences between the two devices under test (DUT), I ask one of our staff to help me in what's known as a single blind test (SBT). The rules are simple. The two DUT are labeled as A and B by the helper so that I do not know which is what. I then go back and forth at my leisure between A and B and choose which sounds better. Only after making my choice am I told the identity of A and B.
For what we do, SBT testing is superior to DBT for a number of reasons, chief among them is the relaxed nature of the test. If the person evaluating the gear feels in control they can take it at their own speed and make judgments without prejudice. The efficacy of this process is superior to DBT because it gets rid of all the negative crap we read about the DBT. DBT testing may be the gold standard for some trials, like drugs, but it fails when applied to tasting, listening, feeling, and those human endeavors where emotions influence outcomes.
The next time you read about, or are asked to participate in, a DBT for stereo equipment, respectfully disagree with the conclusion or decline the invitation. Instead, help those mired in scientific dogma to understand things are never so simple as to be required to discover truth. There can be mulitple paths that lead to the same correct answer.