His voice is very light (hardly audible).

His voice is so light (you can hear the embroidery needle fall to the ground).

His voice is very light, ie he needs to concentrate to hear clearly.

His voice is so low that he can hear footsteps at the door.

Basic requirements for filling in the blanks:

Fill in the blanks is one of the basic questions. When solving problems, it is necessary to have reasonable analysis and judgment, require that every step of reasoning and operation is correct, and also require that the answers are expressed accurately and completely.

Reasonable reasoning, optimized thinking and less thinking will be the basic requirements for solving fill-in-the-blank questions quickly and accurately.