Click here to purchase the entire book in PDF format. A short mis-informed history Once upon a time, it was easy to determine whether one piece of audio gear was better than another. All that was required was to do a couple of measurements like the frequency response and the THD+N. Whichever of the two pieces of gear measured the best, won. Then, one day, someone invented perceptual coding (see Section ). Suddenly we entered a new era where an algorithm that measured horribly with standard measurement techniques sounded fine. So, the big question became ``how do we tell which algorithm is better than another if we can't measure it?'' The answer: listening tests! Of course, listening tests were done long before codec's were tested. People were testing things like equal loudness contours for decades before that... However, generally speaking, that area was confined to physiologists and physiologists - not audio engineers and gear developers. So, today, you need to know how to run a real listening test, even if you're not a psychoacoustician. This, short and intentionally distorted history lesson illustrates an important point that I want to make here regarding the question of exactly what it is that you're intending to find out when you do a listening test. Many people will say that they're doing ``subjective testing'' which may not be what they're actually doing. Option 1: You're interested in testing the physical limits of human hearing. For example, you want to test someone's threshold of hearing at different frequencies, or limits of frequency range at different sound pressure levels, or just noticeable differences of loudness perception. These kinds of measurements of a human hearing system are typically not what people are talking about when the words ``listening test'' are used. Option 2: You're interested in testing how sounds are perceived. For example, you want to test whether people perceive a mono signal produced by two stereo speakers differently than a stereo signal from the same speakers. Almost everyone will agree that these two stimuli sound different. We might even agree on which is wider, or more spacious, or more distant, or more boomy... we can test for various descriptions and see if people agree on the differences in the two stimuli. Option 3: You're interested in what people like - or maybe what they think is `better' or `worse' - or maybe just what their preference is. As we'll see in the next section, all of these options require that you do a listening test, but only one of them requires a subjective test...