Answer:
The major cause is "lack of high frequencies in a sound wave".
Explanation:
- Muffling derives from either the absence of such a radio signal of a higher or specific frequency. This very same phenomenon has been observed whenever you overhear conversations through some kind of wall and perhaps door.
- The approach is equalization. This method helps them to raise those frequencies although these overprotective wavelengths decrease.
So that the above would be the correct solution.
