Twelve equal temperament:

Twelve equal temperament, also known as "twelve equal temperament", is a common method in the world that divides a group of notes (octaves) into twelve In the temperament of semitone intervals, the ratio of the vibration numbers between two adjacent temperaments is exactly the same. Twelve equal temperament refers to dividing the octave interval (second octave) into twelve equal parts in equal proportion according to frequency, and each equal part is called a semitone, that is, a minor second. A major second is two equal parts. There are some amazing coincidences in dividing an octave into 12 equal parts. The frequency ratio of the two tones of the pure fifth interval (that is, 2 to the power of 7/12) is very close to 1.5. The human ear can basically not hear the fifths of the "law of fifths" and "the equal temperament of twelve". The difference in musical intervals. The twelve equal temperament is widely used in symphony orchestras and keyboard instruments. Today's pianos are tuned according to the twelve equal temperament.

The law of fifths:

The law of fifths is based on the pure fifth relationship between the second and third partials of a compound tone, that is, starting from a certain tone and going upward Push a perfect fifth to produce a minor harmony, and then push up a pure fifth from the minor uniformity to produce another harmony. The rhythm determined by such continuous mutual generation is called the law of mutual generation of fifths. The pitch relationship between the seven basic tone levels set out in the law of fifths is slightly different from the pitch relationship between the seven basic tone levels in the equal temperament of twelve.