In music, pitch is the psychological associate of the fundamental frequency of a note. The note an above middle C played on any instrument is perceived to be of the same pitch as a pure tone of 440 Hz, but does not essentially contain a partial having that frequency. Furthermore, a slight change in frequency need not lead to a perceived change in pitch, but a change in pitch implies a change in frequency. In fact, the just perceptible difference is about five cents, but varies over the range of hearing and is more precise when the two pitches are played at the same time. Like other human stimuli, the perception of pitch also can be explained by the Weber-Fechner law.
Pitch also depends on the amplitude of the sound, especially at low frequencies. For instance, a low bass note will sound lower in pitch if it is louder. Like other senses, the comparative perception of pitch can be fooled, resulting in "audio illusions". There are several of these, such as the tritone paradox, but most especially the Shepard scale, where a continuous or discrete sequence of specially formed tones can be made to sound as if the sequence continues ascending or descending forever.
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