You can try it yourself several times. First, set the power, speed and frequency as intermediate values, and set them as high and low keys. If you want to play dark black, you usually have high power, low speed and frequency, but plastic bubbles easily, so depending on the specific material of your plastic, you can only try it slowly. Five-value adjustment of power and frequency, and five-value adjustment of speed. Fix two parameters at a time and adjust only one parameter.