Psychoacoustics and loudness perception

Figure 11.8: Contours of equal loudness perception as a function of frequency.

The area of psychophysics, which was introduced in Section 2.3, becomes specialized to psychoacoustics for the case of auditory perception. Stevens' law of perceived stimulus magnitude and Weber's law of just noticeable differences (JNDs) appear throughout the subject. For example, the exponent for Stevens law (recall (2.1)), for perceived loudness of a $3000$ Hz pure tone is $x = 0.67$ [316]. This roughly means that if a sound increases to a much higher pressure level, we perceive it as only a bit louder. A more complicated example from psychoacoustics is shown in Figure 11.8, which are contours that correspond to equal loudness perception as a function of frequency. In other words, as the frequency varies, at what levels are the sounds perceived to be the same loudness? This requires careful design of experiments with human subjects, a problem that is common throughout VR development as well; see Section 12.4.