The white keys represent the original sounds of the seven sounds 1, 2, 3, 4, 5, 6, 7 (c, d, e, f, g, a, b) in the basic syllable. The black keys are the variations of the above seven basic sounds (i.e., sharp or flat), such as sharp 4 (sharp 4), flat 7 (b flat), etc. Seven white keys plus five black keys form the equal temperament of twelve.

Twelve equal temperament, also known as "twelve equal intervals", is a music law method. Simply put, it divides a set of notes into twelve semitone intervals. The so-called "group of tones" is what we usually call an octave (that is, from 1 to high note 1 in the simplified notation). The method of dividing this group of tones by the equal temperament is to proportion the intervals of this octave according to the frequency. Divide it into twelve parts so that the ratio of the vibration numbers between two adjacent rhythms is completely equal. We call each equal part a semitone, and the two semitones together are called a whole tone. The piano is designed according to the twelve equal temperament, and its two keys are separated by a semitone. For example, the white key that produces the sound "do" is separated by a semitone from the black key to the right, and the black key is separated from the white key to the right by a semitone. In this way, starting from the white key that pronounces do, the seven white keys adjacent to the right (corresponding to the seven sounds do, re, mi, fa, sol, la, and si respectively) form an octave, but these seven There are only five black keys in the middle of the white keys. This is because according to the equal temperament method, there is only one semitone between the mi sound and the fa sound, so there is no need to insert another black key.