First of all, you need to know some physical knowledge, that is, how sound is produced and how sound level works.
Sound is the result of the vibration of the vocal body, and the frequency of the vibration of the vocal body determines the sound level. This is a basic concept. The sound we use in music is music. Therefore, the physical properties of music and sound are the same, and the only difference is the identity and stability of the vibration of the vocal body, that is, not all the sounds used are music, and only those with stable and clear vibration frequency can be used as music.
Music has four basic attributes, all of which are related to the vibration state of the vocal body. The first is the relationship between pitch: the higher the vibration frequency, the higher the pronunciation. In the concepts of "scale", "scale" and "interval", pitch is its measure.
Secondly, the duration of the sound, that is, the relationship between the length of the sound, the longer the vibration of the vocal body is maintained, the longer the sound is.
Thirdly, the strength of the sound, that is, the volume. The volume is related to the amplitude of the sounding body. The greater the amplitude, the stronger the sound. Beat describes the relationship between the length of sound and the strength of sound.
The last attribute is timbre, and the vibration of the vocal body is resonant. The so-called resonance means that the whole vibration and local vibration of the sound generator are not at the same frequency, but multiple frequencies exist at the same time. The more harmonious the relationship between these frequencies, the more beautiful the overall timbre, and the worse the timbre. Chords use this principle to coordinate multiple musical notes.
Learning music theory, even music, must treat every sound in a related way. If you can't see the relationship between each tone, you can't understand the relevant knowledge of music theory.
A scale and a scale are both for a group of sounds. First of all, this group of sounds is not randomly selected, but starting from a core sound, we find other sounds in the middle of this group according to a certain relationship, and then put these sounds in an octave and arrange them in high and low order, thus forming a scale. In a scale, each tone is arranged from low to high, and the position of each tone in this arrangement order is its sound level. The first sound is the first sound and the second sound is the second sound. ...
Interval is simply the difference between two tones, that is, the distance from bass to treble. We should start with the vibration frequency of the sound generator in detail. The level of musical sound is determined by its vibration frequency, but the human ear is used to the ratio of its vibration frequency when distinguishing the relationship between musical sound and height. In a specific interval relationship, the vibration-frequency ratio of two sounds is fixed. For example, if the two tones are high octave and low octave, the vibration frequency ratio of bass and treble must be 1: 2, that is, the vibration frequency of treble is twice that of bass.
In the law of twelve averages, an octave can be divided into twelve equal parts, that is, twelve semitones, and the vibration-frequency ratio between adjacent sounds of every two semitones is the same, that is, the treble is 2 to the power of112. In this way, the pitch of each tone in the scale and their tone sandhi are determined.
Each semitone is the basic sound difference of an interval. But what really determines the number of intervals is the difference between notes.
Firstly, it is stipulated that the interval between two notes of the same level is one degree. In the middle of two different sounds, the bass is the first sound of the scale, and then arranged in the order from low to high. So, at what level of the scale, how many degrees are there between the two notes? For example, how to judge the interval relationship between the C sound and the G sound-if the C sound is arranged as the first-level G, it is CDEFG, the G sound is in the fifth-level position, and the interval between C and G is five degrees. And it's pure fifth, because there are seven and a half notes in it. If G is lowered by a semitone, the intervals of C and bG are still five degrees, but their intervals will be reduced by five degrees because they are missing a semitone. If bG is changed to #F, the pitches of bG and #F are the same, but their meanings in intervals are completely different. C to #F and C to bG are also six semitones in the middle, but the former is increased by four degrees, because C to F are pure four-degree intervals. Major intervals, minor scales, pure intervals, increasing and decreasing intervals, etc. All refer to the different properties of the interval.
So when calculating intervals, scales determine the number of intervals, and semitones determine the nature of intervals.
Interval is a very important concept in music theory, which is used in almost all knowledge related to pitch. Including the explanation of chord structure.