Octave species various available intervals could be combined in any order, even restricting species to just the diatonic genus would result in twelve ways of dividing the octave (and his 17th-century editor, Marcus Meibom, pointed out that the actual number is 21), but "only seven species or forms are melodic and symphonic" . Those octave species that cannot be mapped onto the system are therefore rejected . In chant theory beginning in the 9th century, the "New Exposition" of the composite treatise called "Alia musica" developed an eightfold modal system from the seven diatonic octave species of ancient Greek theory, transmitted to
Octave experience octave equivalency, and its biological basis apparently is an octave mapping of neurons in the auditory thalamus of the mammalian brain. Studies have also shown the perception of octave equivalence in rats , human infants , and musicians but not starlings , 4–9 year old children , or nonmusicians . Most musical scales are written so that they begin and end on notes that are an octave apart. For example, the C major scale is typically written (shown below), the initial and final C's being an octave apart. \override Score.TimeSignature #'stencil = ##f \relative c' { </score> Because of