Now the standard sound is 440HZ, two octaves apart. That is, 880HZ is an octave higher than the standard sound, and 220HZ is an octave lower than the standard sound. Octave wavelength is an integer, and the auditory effect is similar. This is the first one to be decided.
The ancients didn't have high-tech musical instruments now, so they used strings to determine the pitch.
The half chord is an octave higher than the whole chord.
On the basis of octave, it is a later practice to divide the pitch into 12 parts, and the earliest practice is to divide the strings according to Pythagorean theorem.
According to mathematical formulas (there are many formulas. . . ) divided into different intervals, fifth, third, fourth, sixth and so on. .
Finally, on the basis of all intervals, the minimum unit semitone is obtained.
There are some methods of tuning, the second half is different and the tonality is different. For example, c and d in the fifth degree law are not the same sound, and there are some differences.
The law of twelve averages seems to make keyboard instruments and complex music.
I have written so much, hoping to help the landlord. .