The sound produced when the erhu is played is the sound produced by the regular vibration of the erhu strings through the friction of the horse's tail. The so-called regular vibration, that is, when the chord length between the erhu yard and the thousand jins vibrates as a whole, its half, one third, one quarter, one fifth, two fifths... · (in theory, even infinite subdivisions) are all vibrating at the same time. When the whole vibrates, it produces the lowest fundamental sound, while the segmental vibrations produce a sound different from the fundamental sound—overtone. Therefore, a musical tone we usually hear, although it feels the lowest fundamental tone, is actually a complex tone including the fundamental tone and a series of overtones, which are produced by our fingers in real time. If you lightly touch one-half or one-third of the string with your fingers when you play, the sound is an overtone.

The overtones played by the erhu are divided into two types: "artificial overtones" and "natural overtones". Natural overtones must be produced by the vibration of the whole string. When playing, the force of pressing the string with the left hand should be very light, while the force of the bow with the right hand is relatively heavier. Artificial overtones vibrate with the chord length of the finger tone. In actual performance, natural overtones are used relatively more, and artificial overtones are more difficult to play.

There are generally the following five natural overtones used in erhu performance, that is, at 1/2, 1/3, 1/4, 1/5, and 2/5 of the whole string. For example, there are treble 15 and treble 13 on the inner strings of strings 1-5 (forgive me, the treble point cannot be represented here), the overtones at 1/5 and 2/5 are the same. With one-half the length of the string as the limit, there are four natural overtones up and down. That is: at 1/5, the inner string treble 3, the outer string treble 7; 1/4, the inner string treble 1, the outer string treble 5; 1/3, the inner string treble 5, the outer string treble 2 ; At 2/5, the inner string treble 3, the outer string treble 7; at 1/2, the inner string treble 1, the outer string treble 5. Take one-half of the chord length as the dividing line, otherwise the chord segments below are the same.

Artificial overtones are obtained by pressing the sound with the index finger and little finger of the left hand. Its playing method is to press the index finger on a certain phoneme, and at the same time, the little finger floats on the perfect fourth phoneme above it. For example, press on the 1st-5th string on the 2nd, and at the same time press the little finger to float on the 5th, so that you can get a high-pitched 2 that is two octaves higher than the 2nd. By analogy, a total of eight artificial harmonic pitches can be derived for the inner and outer strings. Artificial overtones can only be played in the range of the upper position, and the effect is very poor in the middle position. In addition, there are fifth artificial overtones. If the index finger presses the 2nd tone of the 1-5 string, the little finger floats on the pure fifth above it, that is, the 6th tone of the inner string, and the fifth artificial harmonic treble 6 can be obtained.

Overtones are generally used for long notes at the end of some songs that are not too strong. When used in music, they are used to express deep and distant or distant and slightly bright emotions.