(1) Program material must include critical passages that enable audible differences to be most easily heard.
(2) Listeners must be sensitized to a audible differences, so that if an audible difference is generated by the equipment, the listener will notice it and have a useful reaction to it.
(3) Listeners must be trained to listen systematically so that audible problems are heard.
(4) Procedures should be "open" to detecting problems that aren't necessarily technically well-understood or even expected, at this time. A classic problem with measurements and some listening tests is that each one focuses on one or only a few problems, allowing others to escape notice.
(5) We must have confidence that the Unit Under Test (UUT) is representative of the kind of equipment it represents. In other words the UUT must not be broken, it must not be appreciably modified in some secret way, and must not be the wrong make or model, among other things.
(6) A suitable listening environment must be provided. It can't be too dull, too bright, too noisy, too reverberant, or too harsh. The speakers and other components have to be sufficiently free from distortion, the room must be noise-free, etc..
(7) Listeners need to be in a good mood for listening, in good physical condition (no blocked-up ears!), and be well-trained for hearing deficiencies in the reproduced sound.
(8) Sample volume levels need to be matched to each other or else the listeners will perceive differences that are simply due to volume differences.
(9) Non-audible influences need to be controlled so that the listener reaches his conclusions due to "Just listening".
(10) Listeners should control as many of the aspects of the listening test as possible. Self-controlled tests usually facilitate this. Most importantly, they should be able to switch among the alternatives at times of their choosing. The switchover should be as instantaneous and non-disruptive as possible.
