======================
 Definitions of terms
======================

Cent
    Twelve-tone equal temperament divides the octave into 12 semitones of 100 cents each.

Just intonation
    Just intonation or pure intonation is any musical tuning in which the frequencies of notes are related by ratios of small whole numbers.

Middle C
    The fourth C key from left on a standard 88-key piano keyboard is designated C4 (SPN) (Do3).

Octave
    See Scientific Pitch Notation for numbering.

Pitch
    The property of a musical tone that is determined by its frequency

Pitch Class
    For example, the pitch class "C" is the set {Cn : n is an integer} = {..., C−2, C−1, C0, C1, C2, C3 ...}

Quality
    The name of any interval is further qualified using the terms perfect (P), major (M), minor (m), augmented (A), and diminished (d).

Semitone
   A semitone, also called a half step or a half tone, is the smallest musical interval commonly
   used in Western tonal music. It is defined as the interval between two adjacent notes in a
   twelve-tone equal temperament.

Scientific Pitch Notation (SPN)
    According to the Scientific Pitch Notation, A4 corresponds to a tone of frequency 440 Hz, note A
    and octave 4.  A4 corresponds to La3 in Latin notation, where the octave bellow 1 is -1.
    The MIDI specification range from C-1 to G9.

Step
    a degree, grade, or rank in a scale

    the interval between two adjacent notes in a musical scale

Tone
   ...

.. Pn = Pa(12√2)(n − a)