Want to learn to whistle, the sound is similar to that of Shishi or Sisi, but it is a little loudness. . Is this normal?

The main thing is to practice more. Love is the best teacher.

The most important thing is feeling.

First of all, keeping the lower lip properly moist is conducive to air outflow;

Secondly, put your tongue behind your lower teeth naturally (not very useful)

The two ends of the third upper tooth are gently pressed on the tongue surface, allowing air to blow out from the throat, and the lips are slightly closed, leaving a small mouth in the middle.

Fourth, the rest is to adjust the size and airflow of the lips to make it sound. You need to learn it slowly. Once you can make a sound, as for blowing out the tone, that's the easiest thing. Just control the strength of the blown air flow.