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TONE PERCEPTION

While pitch can be understood as a psychological response to frequency without reference to its function within a musical context, tone is frequently regarded as the perception of pitch with respect to a musical context. G Revesz developed what he called the "two-component theory of tone."  The two-component theory distinguishes two properties by which a tone is perceived.

The first such aspect, or component, is one of height.  This is the aspect of tone which we associate with the "highness" or "lowness" of a tone and is as such a correlate of frequency (again, see pitch).

The second component is that of chroma.  Chroma refers to the position of a tone within an octave and is, as such, repeatable or cyclic.  Accordingly, the aspect of a tone's chroma means that a particular tone is repeatable at the octave. This aspect of the tone is sometimes referred to with the term octave equivalence since a given tone within one octave is understood as equivalent to the same tone within another octave.

The notion of octave equivalence is one of the most basic principles of Western music theory.  Moreover, experimental research in hearing has shown that some people can  correctly identify the name of the note (C, C#, D, etc.)-- its chroma--while misidentifying the particular octave--its height.  This suggests that there is a psychophysical basis for it.