Arranging the musical sounds in order of high and low is called a "sound sequence", and each sound in the sound sequence is called a "sound level". Grade - the unit that divides the intervals between the notes in the scale (each independent note in the musical tone system).

On an octave major scale, there are the first and second steps of the scale...the seventh step; in the next octave, the first and second steps are repeated. Second tone level······Seventh tone level. The other names for the seven tone levels are tonic, supertonic, middle, subordinate, dominant, lower middle and leading (usually represented by Roman numerals IⅡⅢⅣVVIⅦ).

The width of a whole tone and a semitone is twice the relationship. One whole tone is equal to the width of two semitones. Divide the distance of an octave into twelve equal parts, each part is a semitone, and two semitones equal a whole tone. In equal temperament, a semitone is the smallest unit of music.

The distance between the basic tone levels is not even, so the twelve semitones constitute a tone sequence with eight basic tone levels. The relationship between the tones of the major scale is whole and half. Whole and half.

Extended information:

The names of basic sound levels are marked by two methods: note name and roll call. The note name of each level is marked by letters. The roll call is represented by pronunciation. Take the key of C major as an example: the note names of the basic note levels of C major are marked from low to high: C, D, E, F, G, A, B, and their corresponding roll calls are do, re, mi, There are seven pronunciations: fa, sol, la, and si.

In the music system, the marks of the seven basic tone levels (note names and roll calls) are used cyclically. That is, after C, D, E, F, G, A, B, it goes back to c, d, e, f, g, a, b or after do, re, mi, fa, so l, la, si, it is still do, re, mi, fa, sol, la, si...and so on.

Reference: Baidu Encyclopedia-Sound Level