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The Shepard-tone contains anywhere between 8 and 12 partials.  Each partial is spanned by an octave.  The amplitudes of the partials has the following structure:
The structure of a tone's partials (its spectrum) is shown here on a log2-frequency axis, with amplitude shown along the y-axis (using some arbitrary, though relative scale) and frequency along the x-axis..  Each solid vertical line represents an octave component.  In the following, two Shepard tones, a semitone apart, are depicted.
The dotted vertical line represents a shepard tone that is slightly higher than that represented by the solid line.  The upward-pointing arrow indicates the "fundamental" of the second tone.  As can be observed, the lower partials have a greater amplitude than their corresponding partials in the first tone, while the higher partials have a lesser amplitude than their corresponding partials in the first tone.  Meanwhile, those partials in the center of the frequency range have pretty much the same amplitude in both sets of tones.
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